Help repairing a Roland TR-626

Gleix · April 30, 2009, 03:25:39 AM

So I picked up a TR-626 with hopes to fix it - I plugged it up and these are the sounds I got from it:

http://cheezer999.googlepages.com/TR-626.mp3

The machine functions 100% mechanically, the problem is the outputs just give sounds like that. I can't seem to figure out what the problem is.

I did discover that by shorting one of the pins on IC 16 with the pins of an output jack it will give me the drum sounds through that output, but with an added buzzing sound (changes with pitch) and also only works for one jack, so I can't use the individual outputs.

Here's a sound of the buzzing changing when I change instrument pitches: http://cheezer999.googlepages.com/VOC046.MP3

If I could even just get rid of the buzzing with the pins shorted and only one output I'd be happy, but I'd really love to get the machine working normally. Has anybody got suggestions for me?

Circuitbenders · April 30, 2009, 10:11:30 AM

Do you know of anywhere with a 626 schematic or service manual?

Gordonjcp · April 30, 2009, 11:38:56 AM

Okay, let's see what I remember...

The resistor pack beside the sample ROM is the DAC. That's fed to the little skinny opamp beside it, and then makes its way to the 4051 multiplexer which switches the individual outputs.

Check for a signal on the common pin, and see if you get any output. If not, change the 4051. They're very common in analogue synths and fail a lot.

Gleix · April 30, 2009, 08:08:17 PM

Pardon my complete ignorance, but how exactly would I go about testing the 4051?

Circuitbenders · April 30, 2009, 09:41:06 PM

You might as well just replace it. You could probably get a 4051 in one of its many guises at any decent electronics store for about 50p

Gordonjcp · April 30, 2009, 10:41:40 PM

Quote from: breakbeatnazi on April 30, 2009, 08:08:17 PM
Pardon my complete ignorance, but how exactly would I go about testing the 4051?

See if there's a signal at the input (it will be all the drum sounds mixed together).

See if there's a signal at the outputs (these will be individual drum outputs).

Gleix · May 01, 2009, 03:24:40 AM

Thanks guys! Gordon, you really know your stuff. I ordered some 4051's.

There are 3 4051's on the board... IC18, 19 and 24. 24 is the one you talked about though and I couldn't get any output from it, so I'll replace it and see how it works.

Gleix · May 07, 2009, 12:44:42 AM

Well, I replaced that 4051 today but to no avail - still acting the same with clicky sounds and everything. I'll try replacing the other two 4051's since you say it's common that they fail. I'll update.

Any other ideas what the problem could be? I can provide pictures.

Gleix · May 07, 2009, 06:18:38 AM

Update:

Yay! Working good as new! It wasn't the 4051 that you mentioned that was the problem, it was one of the other two but it did solve the problem. After I got the new IC's in everything was working except for the cowbell/tambourine sound (can't live without cowbell) so I found which chip had the output for those sounds and realized putting in the new chip screwed with the gold tracing so making a jumper solved that problem. I wouldn't have known to do anything like that, a simple procedure, before gathering information from the people on this forum - it was all just random poking to me.

Thanks Gordon, you really helped - Now I've got a 100% working 626 for $30. It shall be bent in a fine manner!