Friday, February 28, 2014

Jupiter 8 Replacement Faders and Buttons

For those of you looking for working replacement tact buttons for your Jupiter 8, they can be obtained cheaply, and brand new, from Digikey, digikey part number CKN9100-ND . Check them out. They are the same size, pin spacing, etc as the original. You just have to be really careful when you put them in the "actuators", the button caps, as they are called. You must do it slowly using an exacto knife to pry the old button out of the actuator, carefuly spreading the housing away from the button, and then carefully putting the new button into the housing. But it does come out just fine!

As far as replacement faders, these are a bit harder to find. This is not because they are unusual electrically (10k linear is about as common as you can get), it's because they come in such a large housing. One workaround is to disassemble the old fader, if it is beyond cleaning, and then install a new (smaller packaged)  fader into the old housing. If you get one with the right lever height, travel distance, etc, and mount it in the old housing, when you assemble the housing you essentially have a fader that feels great and looks and works exactly the same as the original.

I used part number
BOURNS PTA3043-2015CPB103
for my replacement fader. It is exactly the same electrically, travel wise, taper wise, and has the same lever as the Jupiter original. It is just in a smaller housing, which fortunately mounts perfectly in the Jupiter 8 faders original housing.

A picture is worth a thousand words... see below:

The replacement fader sits atop the PCB from the original fader

From underneath, you can see where tiny holes were drilled to connect the pins from the replacement fader to the pins from the original fader. Of course, I made sure the carbon was severed completely on the orginal fader PCB so as not to be adding a parallel resistance.
When the housing is installed, the fader looks original again, except now it works! From the top, the replacement fader is exactly the same as the original... exact same travel distance and electrical taper.

Tuesday, February 18, 2014

Prophet 600 repair; recoat contacts

Prophet 600

I recoated the contacts on this prophet 600 with the material shown in the image below. This stuff works great on all rubber contacts in keyboards... I have never had a problem with using it and never had a problem with it wearing off over time (although I have only used it for a few years). For contacts that are hard to find, such as the ones in this prophet, it is a great way to restore the functionality of all keys without spending too much money on tracking down parts.

One interesting note about the Prophet 600: it uses the same keybed as the Korg Poly 6. Yes, part for part it is the same keybed.

CircuitWorks keybad repair (bought from BD electronics)

In addition to the contacts, I recapped the power supply, replaced some pots, and replaced the battery. As far as the knobs (red!) I found these nice replacements from . THe original unit was missing all its knobs, and it just didn't seem cost effective to track down 25 prophet replacement knobs.
These knobs are actually for 1/4" round shaft (the prophet uses 1/4" flatted shaft),but they have a set screw in each of them and can be attached easily and securely. The knobs also work with the 1/4" shafts modern cousin, the 6mm shaft, which is almost the same size but not quite.
Since the replacement pots I put on this unit had a 6mm shaft, the knobs were great in that they could be attached to both size shafts.

This is what a repaired contact looks like.

Sunday, February 2, 2014

Tips For Being A Successful Electronics Repair Technician

I have been doing this for a while now. Here are a few tips that I have found useful...if only I followed them more regularly....

1) Anticipate a harder, longer job than what you think. When giving estimates, aim high. I am not  a pessimist by nature, but this is just the way it is... almost every project and repair takes longer than predicted.

2) When things seem too puzzling, when getting frustrated, walk away, at least for a while. Put it away if you can, let it sit for a while. Fresh eyes can make all the difference. So can a bit of research, and a schematic... and a good night's sleep.

3)Some things are not worth fixing. The tough part is to know when to walk away.

4) Test everything BEFORE you start taking it apart, and note all flaws, notify the customer if you find additional things wrong, BEFORE you take it apart. This keeps you from getting blamed for those additional flaws... it's a lot easier to blame the tech for an issue once he has applied a screwdriver and poked round inside your electronic instrument!

5) Only put the repaired item back together enough so that you can safely test it, then test it before you assemble it the rest of the way. This saves the time of complete disassembly when the unit fails. Not only will you be upset to find out you still have problems with your repair, but you will have to take it all apart a second time!

6) Shake it before you put it back together, rather than hearing that screw rattling around inside when you are lifting it off of your bench, all reassembled, thinking it's all done.

7) Mark every connector that you remove with a sharpie, so you are not puzzled about what goes where. Mark the sides of hardware with a sharpie too so you can easily remember where they go when you reassemble. Every time you take something apart, remember you are (most likely) the guy that's going to be putting it back together, maybe weeks from now. Be nice to yourself!

8) finish every job as much as you can before walking away from it. Why have a bunch of half finished things lying around?

9) Keep the screws and hardware in baggies, separated enough so that you don't spend a bunch of time figuring what goes where.

10) start with a clean bench and workspace for every new repair. It's worth it.

11) If you can't find something in the shop, clean up as you look for it. This way, even if you don't find it, at least you wound up with a clean shop.

12)Don't call the customer with good news until you have tested it 100%, and it is 100% together. Otherwise, the customer may be on their way to pick it up and you will be scrambling to remember how to put it back together, or worse yet you might be scrambling to fix an issue you didn't fix completely.

13) Never lose your cool, with the repair or in interpersonal situations either. If a customer is being unreasonable, it is best to be like a professional politician and stay "on message", never getting sidetracked or emotional in a negative way.

KRK Rokit Studio Monitor Repair: distorition and pops on power on


This KRK speaker came to me with extreme distortion and popping on power on. Eventually I was able to narrow the issue down to the 4580 op amps used throughout the preamp circuit board. Not sure if there was an issue with the series of 4580's that were used in production of these "Rokit" studio monitors, but replacing the op amps made the problem go away, permanently. Each time I replaced one the problem improved; when they were all replaced it was gone!.

Below is a picture showing the effected 4580 op amps.

Technics sx-pr603 Digital Piano Repair: frequent lock ups, failure to turn on, intermittent problems and weirdness

This model of Technics Digital Piano (sx-pr603)  suffers from failing lead free solder around the IC's on the main board. Over time, the board heats and cools repeatedly and flexes, eventually cracking the microscopic connections between the surface mount IC's and the main board.

This causes lock ups, failure to turn on, and all kinds of strangeness with the unit.

It IS fixable, and we can fix them here at Offbeat Electronics, however be forewarned that the job generally costs about 250.00, and sometimes a few touch ups are necessary to keep the board running smoothly, in the first few weeks to a month or two after the repair (which are provided free of charge, of course). However, we have repaired these 100% of the time.

Repair consists of reflowing and adding solder around every one of the surface mount IC's. Also, I prefer to move the power transistors and related resistors off of that circuit board and to a separate heat sink, which I mount in the case.

I move them because I feel that the presence of those transistors and resistors introduces a tremendous amount of heat to the circuit board, and exacerbates the issues with the solder. Between reflowing the solder on that board, and removing the hot components from the board, full working order can be reached... I think this is a great sounding instrument, when it works, and worth preserving.

Korg Pad Kontrol Repair: SMT soldering issues


This Korg Pad Kontrol came to me with issues with not turning on. When I disassembled the unit, I noticed that Lead Free Solder was used ("lead free" printed proudly on the circuit board). I applaud efforts at preserving the environment, but also have become aware that in more than a few circumstances I have found lead free solder to fail. For every unit with failed lead-free solder that I have repaired, I am sure there are hundreds that met an early demise and wound up in the landfill. It has made me question the value of lead free solder, especially as an environmentally friendly alternative to good old fashioned lead. So, personally, whenever I see that lead free solder was used, I check especially hard for failed solder connections.

Sure enough, around IC7 I was able to locate broken solder around some of the pads. The board was most likely flexed, and some of the legs of IC7 had pulled up from their pads. You will see in the first picture that one of the legs on IC 7 had actually gotten bent away from its pad; this actually occurred when I touched the leg with a DMM probe, as I was trying to ring out one of the leg to somewhere on the board. Of course, the fact that it moved so easily was a clear indication that the leg was detached from the pad.

Working slowly with a razor blade, I was able to carefully line the leg up again, and then reflowed all the traces around that IC with some fresh solder. With lead in it.

Some pictures of the work are below; you can notice the size of the chip by seeing a penny on top of it.

For work like this, I use a USB microscope, solder paste, and a hot air rework station. Cleanup afterwards is essential, I use a toothbrush and 91% alcohol.