Archive for the 'Repairs' Category

Konami M2 Troubleshooting

I recently picked up 2 “non-working” Konami M2 boards. I’ve since managed to get both of them working. This hardware is actually fairly robust and it took minimal effort to get mine working but a long the way I learned a lot about how the hardware works and some common problems you might run into.

Continue reading ‘Konami M2 Troubleshooting’

ROMIDENT Drag and Drop Tool

What is ROMIDENT and why should you care?

When troubleshooting an an arcade PCB it can sometimes be helpful to compare the ROM data on your PCB to the ROM data within MAME. MAME is more than just a way to play classic games, the documentation within the source code is invaluable to understanding how the hardware works, and the ROMs themselves can serve as a tool to compare and verify the ROMs on your original arcade hardware.

To this end MAME has a great feature called “romident”. You’ll first need to use a EPROM reader/writer to read the data off of you EPROM or mask ROM and save it to a file, then you can check to see if that file exists in MAME by running this command: Continue reading ‘ROMIDENT Drag and Drop Tool’

SUN (NAOMI) Power Supply Re-Cap

The Sun brand JVS power supply units also known as “NAOMI” PSUs due them being most widely used on that platform have become quite expensive in recent years, even worse is that due to their age many are starting to fail. What most people don’t realize is that similar to CRT monitors, power supplies usually fail due to aging capacitors and many can be revived with a simple cap-kit.


Why not just buy a different PSU?
Normal Arcade power supplies only supply 5V and 12V outputs where as the JVS power supply standard requires 3.3V output as well, also there is a specific connector (JST VL) used for JVS power connections where as normal arcade supplies use either screw terminals or Molex connectors. Even if they did support 3.3V output, the output amperage specs for JVS are also higher than what most 15Watt arcade PSUs can provide, some JVS boards have power consumption requirements low enough that this would be ok but others do not.

There are some people who make ATX to JVS PSU adapters allowing you to use a standard desktop PC power supply for JVS arcade boards however PC power supplies are not adjustable and depending on the specific board you’re using and how your specific ATX supply is tuned it may be providing voltages too high or too low to function properly with a JVS arcade board.

Why Replace the Caps?
Over time the chemicals in electrolytic capacitors break down and expand causing them to not work as well as they should which can cause instability and noise in the power output, in worst cases the capacitor housing can crack and start leaking which can cause corrosion of metal parts and erosion to the PCB. I’ve seen these Sun PSUs sell  for $80-$100 in used condition on eBay, many of these are even in need of a cap kit. The very few shops that sell new JVS PSUs charge upward of $300. Meanwhile a cap kit can be purchased for about $8 and with about an hours work can make a dead or unreliable Sun PSU function like new again.

Not to mention spending some time and a little bit of money to repair instead of replace something is much better for your wallet, the environment, improving your skills, and preserving the authenticity of your arcade equipment. It’s win-win from all aspects.

The Cap List
This electrolytic cap list is for the Sun 400-5397-01  model number (the 400-5443 may or may not need the same caps, I didn’t have one available to check). The filter cap is generally very expensive compared to the rest of the list and generally only replaced on an as-needed basis.

C5 – 680uF 200V *Filter Cap
C9 – 47uF 50V
C14 – 22uF 50V
C15 – 10uF 50V
C17 – 1uF 50V
C18 – 2.2uF 50V
C19 – 4.7uF 50V
C21 – 1000uF 10V
C23 – 220uF 25VC24 – 3.3uF 50V
C25 – 330uF 16V
C28 – 2200uF 10V
C29 – 2200uF 10V
C31 – 2200uF 10V
C32 – 2200uF 10V
C34 – 4.7uF 50V
C35 – 2200uF 10V *A small diameter cap is preferred here
C36 – 2.2uF 50V
C37 – 0.47uF 50V
C38 – 3.3uF 50V
C41 – 10uF 50V

Cap Location Map
Here is a map I’ve put together of where each of these caps is located on the PCB and the direction each cap should be facing. When replacing the caps you should take note of the capacitance, voltage and orientation of the old cap to ensure that it agrees with the above cap list and the below cap map. The PCB itself should also note the capacitor number and orientation of each of these caps for further confirmation. I’ve run into other PCBs where the markings on the board didn’t agree with the direction that the old cap was installed, but in my experience the Sun PSUs have always been marked correctly on the PCB.


*The cap map was made from a photo I took of one of the PSUs I performed a cap kit on. take note of the blackened PCB by C28, this cap had already cracked and started leaking on the bottom which also caused the green/black corrosion on the neighboring resistors. Thankfully no permanent damage was done. I should also note that from the outside this PSU was running with zero problems. This was a ticking time bomb and I was lucky enough to notice the bloated and leaking cap before the PSU failed and or more serious damage occurred.

Replacing the Fan
These Sun PSUs also have an fan that can die or become very noisy. its the same size and shape as an 80mm (x25mm) desktop PC case fan. This is a 2-pin 12V fan that uses a 2-pin JST PH connector. Most PC fans wont use this connector but you can either cut off the connector of the new fan and splice on a pig-tail from the old one, or buy a JST PH connector to crimp onto the leads of your new fan.  Either way replacing this fan is another cheap way to keep your power supply running in top shape for a good many years to come.


Where to buy these parts?
You can piece together your own cap kit using parts from Mouser, Digikey or your preferred online parts vendor, most of these stores will also carry the JST-PH connector for the fan as well. 80mm cooling fans can be found anywhere computer parts are sold.

If you’re interested in buying a pre-made cap-kit instead of piecing one together yourself Ian Kellogg sells one and he also sells the filter cap. I don’t know of anyone else making kits for these PSUs at the moment but if you know of any please leave a comment.

Perminent Fix for Drooping Mirror in a 2nd Gen Subaru Legacy

I have a 99 Subaru Legacy wagon with a pretty common problem. The rear-view mirror in these cars likes to droop, it adjusts itself downward whenever you go over bumps. It’s a problem that seems to effect all of 2nd generation legacys (1995-1999 aka the BD or BG chassis). It’s mostly due to the design of the mirror, the ball joint is on the back of the mirror rather than the top, which means in order for it to hold it’s position there needs to be a lot of tension in the joint in order to resist the force generated by the weight of the mirror whenever the car hits a bump.

Having owned several 240SXs I noticed that the S14 chassis (1995-1998) uses a very similar size and shape mirror as the 2nd gen Legacy:


As you can see they both use a similar length arm with a similar shaped mirror and a similar 3-bolt mounting flange. The Legacy mirror is black but the gray color of the 240SX mirror doesn’t matter because it actually matches the gray headliner in the legacy.


What’s not the same about the mirrors the adjustment join:


As you can see the 240SX mirror has the adjustment joint on the top of the mirror which means that any bumps or vibrations will have little effect on the adjustment. Having owned 3 separate S14s I never had any problems with the mirror falling out of adjustment, nor have I ever heard of it being a problem with other owners.

AMAZINGLY the bolt holes on the mounting flange line up perfectly in the Subaru for a 100% bolt on replacement. I used the plastic cover from the S14 mirror  since the mounting flanges are shaped slightly different but it looks right at home in the Subaru, and no more droopy mirror.

Killer Instinct 2 Deconversion

Last month I cam across an eBay auction for a former Killer Instinct 2 arcade machine.  I say “former” because this poor machine was converted to “Turkey Hunter USA”. A conversion generally means spray-painting all of the original cabinet artwork black, replacing the computer board and the marque and finally gutting the old control panel, covering over the original control panel art with new art and drilling fresh holes for the new controls. It’s quite sad to see, and it’s something I hated doing when I worked in an arcade.

Killer Instinct 2 is my all-time favorite arcade game, they’re pretty uncommon to find in arcades these days and they’re fairly uncommon among collectors as well and growing in value.  The cabinet for sale had the turkey hunter controls and PCB removed so it was just a cabinet and monitor with Turkey hunter art work. $200 +another $150 or so for freight shipping. I decided to buy it and this is what I got:

machine_01 machine_02

I had a lot of parts to order, I had to buy buttons and joy sticks, a Killer Instinct Marquee, new control panel lexan overlay and art, and the condition of the monitor and power supply were completely unknown and of course I had to buy a Killer Instinct 2 PCB, without that it’s just a fancy box. Lots of other little things such hardware, wiring, connectors, etc.

Paint Removal/Cabinet:
First thing was getting the paint removed off the original artwork, this was first because I wanted to get it done out in the garage before moving the machine indoors. I first tried a product called Lift-Off, which worked but not very well, I then switched to a different product called Citri-Strip, which was fantastic. The results:

ki2_day3_01 ki2_day3_02

I also attempted to remove the Turkey hunter control panel graphics, after unbolting the plastic overlay I tried both a heat gun and goo-gone to separate the new control panel art from the original control panel art, the results, sadly, weren’t that great:

ki2_day1_03 ki2_day1_04

You can see that the new art work pulled up some of the paint from the original art, leaving nasty white lines of missing graphics. Even if that wasn’t the case there were three additional holes drilled in the original overlay around the player 2 joystick and the colors were all faded and dingy (the Killer Instinct logo on the Control panel top is supposed to be red just like the Killer Instinct logo on the control panel front).

I managed to find a new, never used Killer Instinct 2 marquee, which made for the easiest and best looking part of the cabinet “deconversion” so far.


Of course even this took some work, the marquee was for a conversion kit (meaning for people who wanted convert a non Killer Instinct machine to Killer Instinct 2) so it needed to be trimmed to size.

The power supply was making some horrid noises, it wasn’t even the original power supply. I pulled it and bench tested it and found that the output voltages were way off so it was getting junked. The monitor was making some horrible noises too, the PCB I put int to test it wouldn’t boot (due to the bad power supply) so I couldn’t determine if it worked or not.

For some odd reason there were hundreds of finishing nails among other bits of hardware on the floor so I cleaned all of that up to prevent any electrical shorts and I bought a new power supply, then modified it to fit in the original mounting location (the junk one that came with the cabinet wasn’t original and had just been screwed into the floor)


This let me boot it up but sadly the monitor wasn’t showing a clear image

I pulled the monitor chassis and bought all new capacitors and a new flyback, I also planned to replace a few small parts related to image sync  to fix the horizontal sync issue the monitor seems to be having. Here is the chassis with all of the new parts installed:


No good, after reinstalling the image quality was better but the monitor couldn’t hold a sync; it was even worse than before. After getting advice from a few experts they told me to check that I hadn’t installed one of the new parts backwards… after pulling the board back out again and checking I found that the part in question wasn’t in backwards but the solder joint wasn’t strong enough, fixing that, and reinstalling the board I get a nice stable picture. Some small adjustments still need to be made but on a whole the picture looks great.

Control Panel:
Not only was the original control panel gutted and then drilled out when it was converted but all of the original control panel wiring had been cut out of the machine as well. I had to completely disassemble the control panel and install new tee-nuts for the joysticks. I bought all new buttons, joysticks and switches. I couldn’t find a Killer Instinct 2 control panel harness for sale so I would have to build one. I found a harness for a different Midway game that used the same style connectors and wiring colors so I bought it. Repinned the connectors for Killer Instinct and then routed, trimmed, and crimped a disconnect onto each wire. Here is what I started with (just 2 wires!), and what I built:

ki2_day3_06 machine_04 ki2_day4_05

Control Panel Overlay and Monitor Bezel:
I still haven’t been able to find new control panel art, so I made myself an temporary cover-up out of some black poster board. I also bought a reproduction laser-cut lexan control panel overlay and I had new monitor bezel stickers printed from some scans that I found online.

ki2_day4_09 ki2_day4_08 ki2_day4_07

The Results so far:
So I’ve got all of the electronics fixed and rebuilt the cabinet has been washed clean of all the Turkey Hunter conversion stink, the last bit is to plug in the Killer Instinct 2 PCB I bought and fire it up:

I got a few games in and I’m really happy to have all the work so far pay off.

What’s left to do:
I’ve still got some finishing touches to do here is the list

  • touch up paint on the side art to cover up scuffs and scrapes
  • repaint the front lower section of the cabinet
  • replace a coin door light bulb
  • find and install a bill collector blank for the hole in the coin door
  • find and install a proper control panel graphic
  • properly mount the KI2 PCB
  • install a cooling fan for the PCB
  • fine-tune the convergence on the monitor
  • built a light shield to prevent the marquee light from bleeding onto the monitor bezel
  • install new t-molding

I’ll get some of the larger items on this list done soon, but other items might take a while to source the right parts. I’ll do an in-depth wrap up video once I’m 100% done.

Stuck Injector

Last weekend I finally got around to fixing the convertible. I got a spare fuel rail from the Fujii boys and replaced the #1 injector.

That’s what I found when I pulled the cap off.  The little metal washer had rusted right to the pin on top of the injector. While I was in there I changed the fuel filter and the spark plugs too. The car is now running better than it has since I bought the thing.


Tore out all the “poorly implemented” wiring in the pickup but I found myself with a number of electrical connectors that weren’t hooked up to anything. The Factory Service manual doesn’t show these… anyone have any guesses? I’ve figured out all the blue connectors, it’s the white ones I don’t know about.

Speakers and Door Cards

Since I’ve been driving the 240 convertible every day I decided to order some speakers to replace the stock ones. I ordered some 4×6 Alpines for the front and some6.5″ Kenwoods for the rear.

Today I decided to tackle the front speakers, it was way more work taking off the door panels than I had anticipated (mostly due to the convertible seatbelt assembly)

While I had the door panels off I decided to fix the door inserts. a common problem on the convertibles is that this fall off, they’re stapled from the factory, and since you basically pull on these whenever you close the door they don’t hold up. I pulled all the staples and used some really short screws, it held on nice and snug now and I’d suspect it will last quite a bit longer than the staples did.

Bose 901 Speaker Restoration

I’ve posted up a new hack page detailing a the Bose 901 Speaker Restoration that I recently completed.

Bose 901 Series IV Speaker Restoration

Bose 901 Speaker Restoration

Last spring I happened to come across a set of old Bose 901s for sale in the marketplace of my local car club… At a price of $25 including the equalizer unit I couldn’t pass it up. I contacted the seller and met him the next day in Manchester to pick them up.

For those of you unfamiliar with the 901s they’re Bose’s Flagship Stereo speaker set and they’ve been essentially the most expensive set of Bose Stereo speakers you could buy for the last 50+ years. They still sell them today, although they’re on “Series VI” now. New a set of Series VI retails for around $1400. Honestly the design of the 901s has barely changed save for the electronics in the “equalizer” module. The cabinet design, drivers, and wiring in speakers themselves haven’t changed functionally since the Series III.

I’m not a huge fan of these speakers but I bought them because my Father is, I really have no need or room for a set of 901s in my house but I figured I could fix up these speakers and it would make a nice Gift at some point.

My father had a set of 901s (Series V I believe) a number of years back and loved them, I remember he always talked about getting a pair way before then, and he was extremely happy when he was able to finally afford a set. Though about 2 years ago he had to sell them. So you can understand why I wasted no time to pick up such a cheap set of easily restored 901s.

What I started with:

Being a Series IV (which sold new from 1978 through 1982) the cabinet style, though functionally identical the series VI (which was released in 1987 and has not changed since) does look quite dated in terms of the grill fabric and cabinet color.

Bose 901 Series IV

Bose 901 Series IV

Removing the Speaker Grills:

Obviously the first thing I did before I could attack the innards was take the original grills off.

Bose 901 Series IV Speaker Restoration - Grills

The front grills are held on with 6 staples, 3 down the left and right sides. They were somewhat difficult to spot. I’ve circled it in the above picture.

Bose 901 Series IV Speaker Restoration - Grills

I started by hammering a cheap screw driver under one of the staples to pop it out a little.

Bose 901 Series IV Speaker Restoration - Grills

I then used some vice grips to yank  the staple out completely.

Bose 901 Series IV Speaker Restoration - Grills

Once the first staple was removed I had enough room to get my hand behind it so I just ripped the rest of the grill off by hand.

Bose 901 Series IV Speaker Restoration - Grills

The front grill frame is made of particle board so the staples ripped right through it, but it doesn’t really matter because I wont be re-stapling it. Once the grill was off pulling out the rest of the old staples with the vice grips was easy.

Bose 901 Series IV Speaker Restoration - Grills

The rear grill was simply attached with some tree-sap like glue, pulling it off by hand was a breeze.

Parts, Costs, and Planning:

Once the Grills were off I could get a good look at the drivers, time had not been kind to the foam surrounds. All of them were rotted, and some had fallen off of the drivers completely.

Bose 901 Series IV Speaker Restoration

Bose 901 Series IV Speaker Restoration

Bose 901 Series IV Speaker Restoration

Bose 901 Series IV Speaker Restoration

Looking closer at the drivers the cones, dust-caps, and voice coils all looked to be in great shape, it was just the foam surrounds that were decaying.

Parts Express sells kits to replace various components, you can buy dust-cap replacement kits, foam surround replacement kits, and if the drivers are so far gone you can even buy replacement drivers.

Bose 901 Series IV Speaker Restoration Parts Express Foam Surround Kit

The kits I needed run $35 a piece and I ordered 2 Bose foam surround repair kits (10 foam surrounds per kit) to replace the foam on all 18 drivers (yes 9 drivers per speaker, each driver is <1Ohm and they’re wired in series). There are other kits available elsewhere for less but I know and trust Parts Express having ordered many times from them in the past.

The only other thing I needed for this project was fabric. Parts Express also sells Speaker Grill fabric but I opted to find some locally. I discovered that my local JoAnn Fabric store sells “Speaker Grill Cloth” for $10 a yard. They were having a 40% off sale so I bought 3 yards for $18 since there are some other projects that I would like to have the fabric for.  Considering the width of the fabric you could easily get away with Just 1 yard for the 901s if you planned your cuts right.

Total cost of these speakers was ~$100 not counting disposables such as razor blades, hot glue, and sandpaper.

Driver Removal:

The first thing I did was remove all the drivers (3 bolts each requiring a 1/4″ socket).

I was somewhat shocked when I pulled out the first driver to discover that they use wire wrap for all the internal electrical connections.

Bose 901 Series IV Speaker Restoration - Wire Wrap Driver Connections

I’d never worked with wire wrap connections before. It seems most electronics had abanoned it before the 80s since the only arcade machines I’d ever seen use them were the extremely old pinball machines from the 50s. even those from the 60s and 70s had moved on to more modern connector techniques.  I also discovered that it was difficult to remove old wire wrap without fitiguing and breaking the wire.

Bose 901 Series IV Speaker Restoration - Wire Wrap Driver Connections

Since I don’t own a wire wrap tool, I decided that I wouldn’t worry about it and would rather just go with a spade style connector or soldered connections when I put the drivers back in. Based on what I’ve read elsewhere it sounds like the newer series 901s use soldered connections anyway.

To ensure I put everything back the way it should be I numbered each of the drivers and each of the mounting locations, I also labeled the wires in the cabinet to ensure I didn’t reinstall any of the driver’s backward.

Bose 901 Series IV Speaker Restoration

Bose 901 Series IV Speaker Restoration

While I was in there I decided to map out the internal wiring. A quick search on google turned up this diagram:

Bose 901 Wiring Diagram

The text listed with the image stated that it was the diagram for the Series II and Series III revisions, I would tend to believe it as it did not at all match the wiring I found inside my pair of Series IV speakers. I’d read that the Series IV through VI used similar wiring. Using the diagram above as a starting point I modified it to reflect the wiring found in my Series IV.

Bose 901 Wiring Diagram

The yellow wire at attaches to the #9 driver goes to the “*” terminal on the outside of the speaker. I’m not sure what this terminal is used for but the labels on the speaker cabinet state not to use it.

Driver Cleanup and Prep:

Before I can do anything with the drivers they need to be cleaned up. All of the old decaying foam surround material needs to be removed and the surfaces cleaned and ready to glue on the new foam.

First thing I did is pull off as much of the rotted foam I could with my hands. Once the bulk was removed I used a razor to cut off as much of the old glued foam as I could,  a fresh blade with sharp edge and the right angle and you can strip it off without much issue. I went over the glue foam on the cone 2 or 3 times taking off progressively more each time, as a paper cone it is extremely delicate so taking your time is preferred.

Bose 901 Series IV Speaker Restoration

Next I used a small screw driver to scrape the old glue off the basket.

Bose 901 Series IV Speaker Restoration

Bose 901 Series IV Speaker Restoration

Once all the material had been removed I rubbed my finger over the foam on the cone to loosen up and brush off any dust or small particles that remain. Then I went over the whole thing with compressed air to remove any particles left, taking caution to make sure there isn’t anything under the cone.

Finally I went over the basket surface with isopropyl alcohol to make sure it’s completely clean, I don’t do this on the basket surface as it could damage the cone.

Bose 901 Series IV Speaker Restoration

Now I have a nice clean driver ready to receive a new foam surround.

Bose 901 Series IV Speaker Restoration

Installing the Foam Surrounds:

I started by placing a bead along the edge of the cone as well as one along the inside edge of the foam surround.

Bose 901 Series IV Speaker Restoration

I used the swap to spread it out a bit, I did a little more after the above picture was taken, you want a nice thin, even layer over the whole area to be glued.

You should let the glue “set” for 5-7 minutes before attempting to stick the two sides together, it turns clear when it’s ready. Most of the time I found it was easier to know when it was ready by the clarity of the glue rather than some arbitrary amount of time.

Centering the foam surround is CRITICAL. the cone sticks up past the basket slightly, so I placed the ring, then pushed the cone down slightly and made sure that the ring is centered on the basket, then when I relieved pressure on the cone it would center itself.

Bose 901 Series IV Speaker Restoration

After that I went around the edge of the cone applying pressure to ensure good adhesion.

Only the center part of the foam is glued at this point. It needs to setup for at least an hour before the outer edge of the surround could be glued. To be on the safe side I let them sit over-night before continuing.

Once the glue has dried on the inner portion of the surround I could begin gluing the outer edge.

I started the outer edge by first running a bead along the flat surface of the basket.

Bose 901 Series IV Speaker Restoration

Then I put a small amount of glue under the edge of the foam surround, this is a pain since you have to peal the foam up with your hands and spread the glue over a small section at a time until you’ve gone around the entire edge.  This is also why you need to let the glue on the inner edge completely dry before attempting the outer edge; the stress of pealing up the foam could compromise the adhesion on the inner edge.

Bose 901 Series IV Speaker Restoration

Once the glue has been placed I used one of the included swabs around the parameter smoothing and evening out the glue on both surfaces.

Bose 901 Series IV Speaker Restoration

Like the inner edge, I let this set for 5-7 minutes before affixing both surfaces, they wont touch since the cone naturally sits up higher than the basket.

Centering the outer edge is perhaps even more important than centering the inner edge. The reason being is that any mistakes made on the inner edge can be corrected with the outer edge, so there is no room for error.  If not centered properly the cone will not be able to move up and down smoothly and the sound quality with be severely diminished.

To ensure it’s centered I used a bottle of water, with just enough water to push the cone down without crushing it. The water also ensures that it’s being pushed straight down and perfectly centered. My kit didn’t come with any, but some other kits include shims to help ensure that the cone is properly centered during this step.

Bose 901 Series IV Speaker Restoration

Again I go around the parameter applying pressure until it’s affixed well. I leave the bottle on the cone for a minute or two to let it settle to ensure that the foam doesn’t pop back up.

Bose 901 Series IV Speaker Restoration

The glue should dry for at least an hour before you reinstall them. Keeping them on their backs while they dry will help ensure good adhesion.

Reinstalling the Drivers:

I looked into various spade connectors that I could use to hook the wires up to the drivers but alas I couldn’t find any that were worth using. Without the proper tool to do wire wrapping I ultimately decided to just solder them back together, I don’t really plan on taking these things apart ever again so I might as well. Reading around I get the impression that the Series V and VI use soldered connections on the drivers anyway.

I started by ensuring I had straight/stripped wire ready on each connection, I used a slight bit of sand paper to take the dust and coating off the wires, they have a coating to prevent oxidation but it also hinders soldering (since it was designed for wire wrapping) just a light sanding is all that was needed to ensure that the solder will stick well.

Bose 901 Series IV Speaker Restoration - Soldering

I did the same on the drivers, only I used a screw driver to scrape it off since it was much thicker and heavier on the wire posts than on the wires themselves.

Bose 901 Series IV Speaker Restoration - Soldering

I tinned both the posts on the drivers and the wires.

Bose 901 Series IV Speaker Restoration - Soldering

Once everything was tinned I soldered each of the driver’s connections, tore off my wire markers (I wouldn’t want them buzzing inside the speaker once it was all back together).

Bose 901 Series IV Speaker Restoration - Soldering

After soldering each driver I bolted them back into the cabinet before starting to solder the next. I also re-used the original foam isolator that goes between the driver and the enclosure, these were still good and they keep the drivers from buzzing or rapping against the enclosure.

Since the wires were short I did the bottom row of speakers first, then flipped the enclosure upside down and did the other row, it saved me a 3rd hand.

Bose 901 Series IV Speaker Restoration

Bose 901 Series IV Speaker Restoration

Once the speaker has all the drivers back in place it is functionally restored.

At this point I tested the speakers. They sounded great but I did notice that one of the terminals was lose, so I pulled out the nearest driver so I could tighten the screw on the inside.

Bose 901 Series IV Speaker Restoration - Testing

Grill Cleaning and Prep:

Now that the speakers were functionally restored, all that was left was to make them look a little more up to date. I decided that the wood coloring wasn’t all that bad, and while the cabinets had some scuff and scratches my wood finishing abilities have something to be desired. In the end the only updating I would do is the grill cloth, replacing the ulgy Tweed with some new, more modern black acoustic fabric.

Before I could do anything though I had to strip down the old grills to their bare frames.

I started by removing the push pin badges from the front grills.

Bose 901 Series IV Restoration - Grill Badge

The fabric on the front grills was easy to remove just pulled it off with my hands and spayed it with some compressed air and they were ready for new fabric.

Bose 901 Series IV Restoration - Grill

The rear grills needed a little more work before they would be ready for fabric though.  I used a razor blade to separate the plastic port hole trim pieces from the grill, then pulled the material off by hand just like the front, then I used a razor to clean up all the large glue bumps left around the port hole areas.

Bose 901 Series IV Restoration - Grill

Unfortunately there were little bits of tree-sap glue as well as tweed “fur” stuck all over the grill frame to the residual contact cement.  To get rid of this I took a block sander and sanded it down to remove all that. Then I dusted it with a damp rag then once dry I went over it with compressed air for a nice clean and smooth grill frame.

Bose 901 Series IV Restoration - Grill

Grill Re-Upholstering:

Now that the front and rear frames were prepped they were ready to be reupholstered. I’m not much of a fabric person so I just did what made sense to me, overall I was pleased with the outcome though.

I started with the front grill. I laid the grill down on top of my fabric and cut around it so the fabric stuck out roughly an inch around the parameter of the frame.

Bose 901 Series IV Speaker Restoration - Grill Reupholstering

Normally acoustic fabric is installed using a spay on contact cement.  I really hate working with that stuff, and acoustic fabric is stretchy in all directions, so I decided I would just work my way around with some hot glue. It worked exceptionally well. After each tack I’d check to ensure I wasn’t introducing any wrinkles on the other side.

Bose 901 Series IV Speaker Restoration - Grill Reupholstering

After I was done gluing I went around and trimmed off all the excess material.

Bose 901 Series IV Speaker Restoration - Grill Reupholstering

Finally, I put the badge back in place though the original hole to complete the front grill.

Bose 901 Series IV Speaker Restoration - Grill Reupholstering

For the rear grilsl I started by cutting, gluing, and trimming the fabric just like I did on the front grills.

Bose 901 Series IV Speaker Restoration - Grill Reupholstering

Once the fabric was glued and trimmed I cut an X one of the port hole areas with a sharp razor.

Bose 901 Series IV Speaker Restoration - Grill Reupholstering

I then pressed the port hole trim through, checked for wrinkles, and trimmed up the excess fabric.

Bose 901 Series IV Speaker Restoration - Grill Reupholstering

After that I hot glued the trim ring in place (which also helped secure the fabric around the ring as well). Following that procedure for the rest of the port hole openings the rear grills look nice and neat when done.

Bose 901 Series IV Speaker Restoration - Grill Reupholstering

Once all 4 grills had be reupholstered I hot glued them back onto the enclosure. I figured this would be more visually appealing than re-stapling the front or finding some kind of replacement glue for the rear. Hot glue holds securely but can also be easily pulled off if need be.

The front grills were tacked in six spots where the staples used to be.

Bose 901 Series IV Speaker Restoration - Grill Reupholstering

The rear grills were tacked in ten spots where the “tree-sap” glue used to be.

Bose 901 Series IV Speaker Restoration - Grill Reupholstering

The Results:

Overall I’m quite happy with the results, with a few days worth of work and relatively little money spent I ended up with a nice looking and nice sounding set of classic stereo speakers. Hopefully they’ll seem some good use in years to come.