Tag Archives: repair

Replacing the backlight of a Roland MKS-80 rev 5

Today I changed the backlight on a Roland MKS-80 rev 5. If the backlight is very weak, the electro-luminescent foil it’s probably worn out. They simply have a limited lifetime. When this happens you have three choices;

  1. Ignore the problem and use a flashlight
  2. Replace the whole LCD
  3. Replace the foil

I think the missing backlight is really annoying and makes the synth harder to use, so not doing anything was not an option.

Replacing the LCD would probably not be too hard, it has standard dimensions of 80×36 mm and are cheap. If you’re lucky a new LCD would just work, but in the worst case there could be compatibility problems. I’m not saying there will be problems since I haven’t tried it, but there’s an obvious risk. For example, changing the LCD on an EII to modern LCD also required changing a chip, otherwise the LCD just displayed strange characters.

I went for the third option, namely just replacing the foil. There are some companies providing replacement foils cut to the right size in various colors. However, I thought I’d give Roland a try since they seem to have a lot of old stuff left in stock. So I emailed Roland Scandinavia asking for a foil for a Roland MKS-80 rev 5. Since they didn’t know exactly what part was, they emailed me the service manual for me to look up the part number.

After browsing the manual I finally found what I suspected was the correct part, namely “15029181 EL-101 (electro luminescence)”. Roland said it’d be around €20 and recommended me to visit my local Roland retailer to order it, so I did…

Replacing the foil is quite straight ahead. Most of the work is getting to the LCD. To do this you of course have to remove the lid, and then the front panel. Then you have to undo three screws and three standoffs so you can fold the two voice boards upwards to finally reach the CPU-board at the bottom which the LCD is connected to in three places. Two of the connectors are snapped in place, so use a small, flat screwdriver to fold the latches away. Then you finally remove the four screws holding the LCD in place, remove the LCD and heat up your soldering iron.

I used desoldering wick to remove the old solder. Then it’s just a matter of sliding the old foil out of the LCD. The “new” one I got from Roland is probably NOS, because it looked exactly the same as the original one. I slid it into the LCD and soldered it’s two legs to the circuit board. I actually cut away about two mm of each leg since they were a bit too long. I powered the MKS-80 up, and the backlight was really bright – success! However, it seems that I should have placed it a little more to the right.

Then it was just a matter of reassembling the MKS-80. However, this was not as easy as disassembling it. The tricky part is the front panel that has three rectangular holes for the OMNI, POLY, MONO leds. The leds have to go straight in their holes, otherwise the front panel won’t sit where it should. There’s also a similar led for MIDI MESSAGE to the right which makes it even more trickier… Do not try to force the front panel, just take it easy and align the leds, and do try not to get too annoyed.

I put the MKS-80 back in the rack and fired up my DAW to realise that the MKS-80 sounds great and the backlight is strong – but – the MIDI MESSAGE led doesn’t work… I will replace it some other time.

E-MU Emulator II key fix

Oddly enough, the E2-key on my EII didn’t trigger as it should, it was triggering very randomly. I suspected this was due to oxidation and opened up the EII.

Removal of a key is simple, but you have to be careful not to break the now 30 year old fragile plastic. You simply push the key downwards at the front, and then pull it backwards towards you.

I removed both the E2 key and its neighboring F2 key to get a better view. Underneath the key there’s a rubber mat which the key pushes on. Underneath the rubber mat is a small metallic surface that pushes another surface on the EII which results in a contact.

Lifting the rubber mat showed serious oxidation on the surface on the EII. I sprayed a cotton swab with electronics cleaner and cleaned the surface from oxidation. After that I put the keys back to test if the problem was solved, which it was!

When the keys were loose, I cleaned them from 30 years of dirt. I was tempted to remove all keys and clean them, but I thought it’s an unnecessary risk due to the keys being fragile.

E-MU Emulator II slider pot A replacement

Sooner or later one of the slider pots will fail on the Emulator. This has happened to the ‘A’ slider on my copy. The fault was that it simply didn’t work, no values were changed when sliding it. When I bought the EII, this slider was also missing a cap, so it wouldn’t surprise me if someone had done something to it before.


Replacement sliders can be bought on eBay for $15 + shipping or much cheaper somewhere else. I bought the exact same slider pot and capacitor at my local store, Electrokit, and it set me back $4 in total.

These are the parts that I got:

  • Slider pot 60mm 10k lin 40920001

  • Ceramic 100nF %0v Y5V axial capacitor 41003074

A few months ago I also bought a new slider cap on eBay for $5 + $2 shipping, it could probably be found somewhere else much cheaper.

It’s important to make sure that the slider has the correct form factor, in this case the “arm” that the knob will sit at was 5mm too short. On the other hand, the original sliders are mounted with 5mm nylon washers between the board and the slider. By skipping the washers, the new slider arm got the exact same height as the original ones. I stupidly forgot to photograph it…

Worth mentioning is that the four pins on the slider were positioned differently than on the original. They did have similar markings though: 1, 2, 2, 3.

Replacing the slider

The replacement process itself is very straight forward. Start by opening the EII and find the upper left board. Disconnect all cables that goes to it, and on the front remove the four slider caps and the volume knob. Finally unscrew six Philips screws and the board is loose.

The slider is then screwed to the board with two smaller Philips screws. I started by desoldering the wires though, before unscrewing the slider. I opened the old slider and it was obviously physically damaged, no wonder it didn’t work.

Then I screwed the new slider to the board without the vinyl washers in between, and soldered the wires and capacitor to the corresponding pin numbers. Luckily the wires were long enough to reach the pins even though the pins were physically in different positions.


I’d say the operation is very easy to do and that the A slider really is something you can’t live without unless you can settle for presets. The A slider is used for fun stuff like cutoff, start- and loop points etc.

Changing battery on the TX-816

Sooner or later the battery will go dead on a TF1 module. It has a standard 3V CR2032 Lithium battery that can be found everywhere. When the voltage drops to low, the TF1 will fail to hold it’s memory and all patches and settings will disappear. Unlike the DX7, each TF1 doesn’t have a cartridge reader, but similar to the DX7 there’s no ROM memory. If you lose or edit the patches, the only way to get the factory patches back is to transfer them by sysex from a computer or another DX7.  The TF1 lits the error led and displays a 4 if the battery voltage is too low.

The error led is lit and the alpha numeric display shows a 4. This means error number 4 = low battery. At the top and bottom you can see the hex screws that need to be unscrewed.
The error led is lit and the alpha numeric display shows a 4. This means error number 4 = low battery. At the top and bottom you can see the hex screws that need to be unscrewed.

As with a lot of synths from the early eighties, when patch memory was a novelty, the battery is soldered to the TF1’s circuit board. So it has to be desoldered to be changed. Then the new battery must be soldered back. One alternative is to put a CR2032 battery holder there instead, then next time no soldering will be required. I chose the battery holder path.

First you have to remove the TF1 module and it’s actually very easy to do. Unscrew two Philips screws on the back, and two screws with 2.5mm hex heads (IKEA style, but smaller) at the front. Then push the card from the back so it pops out of the front. Pull it gently towards you without using any force, it should go smooth.

The TF1 module is nearly out.
The TF1 module is nearly out.

I desoldered the old battery and used a solder sucker to remove the old solder. I then measured the distance between the two holes to approximately 16 mm.

Battery is unsoldered.
Battery is unsoldered.
The space between the battery's legs is 16 mm. Unfortunately I could only find battery holders with 19 mm space.
The space between the battery’s legs is 16 mm. Unfortunately I could only find battery holders with 19 mm space.

Unfortunately I couldn’t find a holder with 16 mm distance between it’s pins, 19 mm was all I could find (bought here). Fortunately the pins were quite long, so I managed to bend them inwards enough for them to fit and penetrate the holes.I then soldered the battery holder and put the battery back.

Look closely to see the bent pins (19 -> 16 mm conversion).
Look closely to see the bent pins (19 -> 16 mm conversion).

A quite simple operation. I think it’s worth the extra time and cash ($2) with a battery holder. That time will be spared next time the battery must be changed.

I recommend this site for more info on the TX-816.

Battery mod and Midi upgrade in Oberheim DMX

Today I did two things on my DMX that should have been done long ago.

First task was to solder in a new battery. The old battery was removed a couple of months ago, but I never put in the new one (bought from Electrongate).  Since I don’t think it’s a good idea to solder the new battery  in the same spot due to possible leaking disasters, I soldered two new wires. The battery was then placed in the bottom right corner and insulated with tape.

A non working chinese iPhone charger cable was used. The battery is placed down to the right, far away from the board.
A non working Chinese iPhone charger cable was used. The battery is placed down to the right, far away from the board.

The next thing to do was installing the Midi upgrade from Electrongate. My Midi upgrade was actually a special order – normally you place the Midi jacks on one of the walnut side panels. I didn’t want to do it for two reasons;

  1. I prefer to have all connections at the rear and second
  2. And most important – mine are mint. It would be shame to drill in them

So I mailed Paul, the owner of Electrongate, asking if it was possible to get the Midi jacks in a breakout box instead. To avoid drilling holes, Paul made a special cable that goes from the Midi board to the 12-pin Molex that was used for triggering. Then the breakout box was connected to the trigger Molex.  A very neat solution – the trigger in functionality was sacrificed – on the other hand I don’t need it when I have Midi.

This breakout box is a special order. Since the walnut panels are mint on my DMX I asked Paul for an alternative. He suggested to use the trigger input port back to get the midi cable through without drilling.
This breakout box is a special order. Since the walnut panels are mint on my DMX I asked Paul for an alternative. He suggested to use the trigger input port back to get the midi cable through without drilling.
This cable is also part of my special order. One side goes to the midi card, the other goes to the cable that is connected to the trigger Molex.
This cable is also part of my special order. One side goes to the midi card, the other goes to the cable that is connected to the trigger Molex.

Installing the kit is fairly straight forward, there’s an excellent guide with photos that is very simple to follow (so I didn’t take any photos). My DMX had the memory upgrade board, in the guide the upgrade is performed on a non memory upgraded DMX, so there were some differences, however – they are pointed out in the text. The Midi board replaces the memory upgrade board and a bonus is that the Midi board actually upgrades the memory as well.

The midi upgrade card itself.
The midi upgrade card itself.

The installation procedure is mostly about taking chips from one place (the main board or memory board) and putting them on the Midi board. I recommend having both an IC puller and a small flat screw driver for this. The hardest part of the upgrade is soldering two tiny wires (“E1” and “F1”) to the main board. It was hard because in one case you have to solder the wire directly to a copper lane, in a very tight place. Another challenge is to cut the copper lane next to it, and then avoid soldering the wire over the cut so that the cut isn’t cut anymore.

I’m not a soldering expert, but if you know someone that can do it for you, or if you live close to Paul, pay him to do it for you!  It took me a couple of hours, and I wasn’t very comfortable cutting and soldering on such an old expensive piece. On the other hand, doing such stuff is the best way to learn.

I took the DMX back to the studio and connected the Midi – it worked flawlessly! Even though the DMX is very fun and easy to program, it’s just more convenient to have Midi. I really feel that I have to modify my Boss DR-110!

Repairing an E-MU Emax having a key always on

I’m about to sell my Emax since I don’t use it very much, and it takes up a lot space. It did have one problem though, that I hadn’t looked into at all. The problem is that as soon as the Emax had loaded a disc, the E4 note was always on. I suspected it had something to do with the that particular key, and hoped that maybe some cleaning with alcohol would do the trick.

I turned the Emax upside down and opened the bottom lid. I must say it’s very easy to open, less than ten screws and then you have access to almost everything. The key error was easily spotted as soon as I got the lid off. The spring wasn’t in position, so I simply put it back, did a little cleaning of the Emax, and put the lid back on. Worked perfectly.

This is the spring that needed to be put back in place. After doing that, that note wasn't always on anymore. A very easy fix.
This is the spring that needed to be put back in place. After doing that, that note wasn’t always on anymore. A very easy fix.

So, if you ever hear about an Emax with an always-on-key, it’s probably a very easy five minute fix.

Some other stuff worth commenting regarding my Emax.

  1.  It has the revision 3 CPU board, I’ve read that this is the easiest one to upgrade to SCSI.
  2. The Emax was probably factory upgraded to SE, all the SE markings are separate stickers as you can see on some photos. The serial number of the Emax is fairly low, so this is one more evidence that this is an upgraded non-SE.

Oberheim DPX-1 alive

Short resume:

  1. I bought an Oberheim DPX-1 from on eBay
  2. The DPX-1 arrived all dented and wouldn’t start
  3. I was refunded (good seller) and bought another one on a trip to Stockholm
  4. I suspected the CPU since one pin was missing. I ordered a new one.
  5. I replaced the CPU and thought the DPX-1 was working.

Then after a few uses it went all bananas again. At this point I still suspected some kind of “software error” because of some faulty CPU or memory.  I disconnected everything, part by part. Still didn’t work. Then I disconnected the lower main board (the DPX-1 has two main boards). The upper board contains the CPU, memory and midi. The lower board contains all audio specific stuff like filters and outputs. As soon as I disconnected the power to the lower board, the DPX-1 booted perfectly. Quite fun that the upper board can work without the lower one powered up.

Anyway, as soon as I connected the lower board again the DPX-1 wouldn’t start. If I booted without the lower board and then connected it, the DPX-1 would hang. So there was something fishy about the lower board. I measured all voltages and they were stable.

So I disconnected the power to the 8-output and cd-rom expansion card and the DPX-1 booted just fine. At this point I was very happy, but that didn’t last long since I had no output. Nothing but very low distorted audio came out of the original single output.

Next thing to try was to remove the expansion card and then I discovered that the cable going from the lower board to the expansion had to be connected to a connector (J8) on the main board below the expansion card. So now there’s a big hole in the back of the DPX-1 – but I can live with that. I don’t think the 8-output expansion is usable anyway. The cd-rom is very rare and only reads cds that also are very rare. The eight outputs work the same way as on the Emax. Each voice has its own output, so every time you hit a key that sample is heard in the next free output. Eight voices = eight outputs. I’ve heard that there are some EII disks with drumkits and stuff that actually maps one particular sample to use one particular output, but I haven’t found one yet.

Boss DR-110 temporarily repaired

Even doctors may need help sometimes… A few months ago, I got my Boss DR-110 that I bought on eBay on which only the HAND CLAP worked. All other sounds were there, but at a very low volume. With the help from the 99musik forum the BALANCE potentiometer became the primary suspect.

A few weeks ago I ordered a new 20KΩ linear potentiometer even thought the dimensions weren’t right, just to verify that the pot actually was the problem.

When looking at the PCB it was quite obvious that someone had try to repair/replace the pot before. It was quite badly done, one of the trace leading to wiper connection on the pot was loose.  I desoldered it and soldered a three lead cable that I inserted through the hole where the pot is supposed to be. I had to scrape the trace where the wiper had been and solder directly to it.

At first I forgot two bridge the earth that normally is though the body of the pot, but since I have no pot but three leads instead, I soldered a new lead to bridge the earth. Then the doctor was alive again! Now I only have to find a fitting potentiometer…