Tuesday, October 15, 2013

Korg Triton Touch Screen Replacement

This Korg Triton came to me with a broken touch screen. The touch screen, or "digitizer" is attached right to the lcd screen, and sits right above it. On this Triton, the digitizer did not work but the LCD was clear and in good condition. A new screen, available here, costs $250.00. This part includes the LCD as well as the digitizer. Replacement digitizers are available on ebay for 50.00 or so, so we went that rout, intending to attach the digitizer to the existing LCD.

The part that arrived looked a little different, but it was the right size. However the cable was smaller. Additionally, the cable is upside down (the conductive area of the pins is on the opposite side). Further, if you look at the picture of the original part, seen below, the pinout of the cable is slightly different. What would be pin 5 on the new screen was routed to pin 8 on the original part. See the picture below.

I was able to salvage a ribbon connector from a salvaged dvd player, and then go through the mental work of connecting the pins in the correct sequence with jumper wires to the korg circuit board. If you don't have a salvagable ribbon connector, I am sure you can find one on Digikey or Mouser, as long as the spacing is correct for the ribbon cable on the new digitzer.

 Routing the wires from the ribbon connector to the Triton circuit board takes some brain work, but I was able to achieve this, and it works perfectly. I routed pins 1 -4 from the digitzer to the same pins on the Korg Triton circuit board.  Pin 5 from the new digitizer goes to pin 8 on the Triton (that's the first one that crosses over.  Pin 6 from the new digitzer then goes to pin 5 on the internal connector, 7 goes to pin 6, 8 goes to pin 7, and if you did it right pin 8 on the Triton is already attached to pin 5 coming from the new digitizer.

This worked, I would recommend not giving up if you don't get it right. Double check your pinout or see if you need to completely reverse the pinout you tried. Don't physically attach the digitizer to the LCD before you are sure it works right, too.

Why not? In my case, I was scratching my head because the X and Y axises seemed to both be reversed on the new touch screen... if moved my touch more to the left, the touch would register more to the right..Ditto for up and down I realized that, rather than fooling around more with re routing pins, this problem was solved by turning the digitizer around 180 degrees. I was glad I hadn't attached the digitizer o the LCD with the double sided tape yet.

Finally, after that I found that the new screen had to be calibrated. The very top areas of the touch screen didn't work. Worse, I couldn't access the calibration feature in the korg because this requires access to the upper right area of the touch screen to accomplish.

Performing a reset does not reset the calibration (enter+o).

However, entering the internal test mode does erase the calibration data... so I was able to do so by doing that. The test mode is entered by pressing 0 + 4 while turning the power on. That info is available in the service manual, which can be googled and downloaded for free.

Finally, since I had done the reset, I had to reload all the factory sounds. I did this using my  floppy emulator drive. These seem to work with the Triton, but you have to play around with the jumper settings, and for me it only worked if I first let the triton format the drive, then put it in the computer and loaded the factory sounds, then moved it back to the Triton.

SO, if you are in a position where you have a replacement digitizer that has the wrong size cable, don't give up, but be prepared for an ordeal, or send it to here Offbeat Electronics and we will do it for you.
The Original Ribbon Cable rerouts some of the pins. This is not done on the replacement.

The original triton digitzer has a wider cable.

Monday, October 14, 2013

Alesis DMPRO repair

Alesis DMpro

 This unit had no outputs when it came to our shop. The issue with these Alesis drum machines is that the filter capacitors fail, and some of the other electrolytics. I believe it is because they are really small.... that's why I always recap the whole unit with higher voltage capacitors, and if they are a little bigger I move them a little bit as shown in the picture below. A small bit of hot glue holds them in place, and they last much longer than the original ones.

Midas Verona Soundboard

At Offbeatelectronics.com, we repair soundboards and mixers as well as keyboards and synths. We do on-site work as necessary, and assure the quality of our work with an excellent warranty.

This particular mixer resides at the Jubilee Fellowship Church in South Denver; an excellent place. This repair was performed on site, due to its large size.

Don't forget a torx screwdriver when taking this thing apart! 

The main issues were the necessity for a thorough cleaning, and deoxidizing. Other issues were the result of some loose ribbon cables between boards, and the most serious issues were broken TRS jacks on the outputs and inputs. On many of the insert jacks, the tip connector was broken off, making the inserts appear to be malfunctioning. It seems that the 1/4" jacks are prone to freeze to the tips of the plugs, and the jacks break when the cable is pulled out.

This unit was in excellent condition after we performed the repair.

These jacks were the culprits in many issues with the soundboard

Roland KR650 repair: bad electrolytic capacitors

This particular model suffers from leaky electrolytic capacitors on the main board. By leaky, I don't mean electrically; I mean there is some nasty liquid leaking out of these things! The result is all kinds of distortion in the outputs, low volume, intermittent problems, etc.

I have repaired a few of these. The repair has always been permanent, however on most instances the liquid that leaks from the capacitors burns through traces on the board. On this one, the liquid burnt out the V- supply to one of the op amps near the DAC chips.

So, the repair consisted of removing all the surface mount electrolytics on the main board, cleaning up all the liquid, replacing the caps, and repairing a trace that supplies the V- to one of the op amps near the DACs.  Other traces may be damaged too, so if it still doesn't work when you replace the caps you will have to check the traces that run near them.

I used standard through hole caps instead of surface mount on this job. I bent the leads and attached them to the pads; there is plenty of room for this, and I applied a bit of hot glue on the leads to hold them in place. If my memory serves, they were all 3.3 and 10uF caps.

The instrument sound great now. I also replaced all the tact buttons. There sure are a lot of buttons on that thing!

Finally, the contacts on this one were good. However, I think this was a transitional model, and the key contacts are no longer available. This may be a consideration in judging the cost effectiveness of repairing this model; if the contacts show signs of failing, it would be worth trying to repair them first (perhaps by recoating them) before investing time and money in fixing the other issues.

The highlighted area is where I found destroyed traces, supplying the V- to one of the SMT op amps near the DACS