SCI Drumtraks Replacing Main Output Jack

Hey folks,

First time poster here, new to synth repairs, but decent with soldering/building. I got a good deal on a Drumtraks a while back because it had a dead output jack. The previous owner said he sprayed contact cleaner into it. I noticed while testing some of the buttons were a bit sticky and the metronome seemed to work intermittently. Those are concerns for another day at the moment- but if anyone has any advice I’d appreciate that as well!

A few main questions:

Does the Drumtraks use a specialty jack, or could someone point me towards a suitable replacement? I opened it up and didn’t recognize the type of jack.

This is my first time doing this sort of work on a vintage piece of gear so are there any special precautions I should take while replacing the jack? Any nearby sensitive components or any way I should go about removing and installing the new jack? I have both desoldering braid and a solder sucker.

I almost hate to ask, but are you sure that the problem is with the jack? Unless it’s physically broken, it’s hard to imagine a jack going bad. (unless that contact cleaner he used has made a mess…)

All good, it’s a good question, as I kind of just took the guys word for it. He was selling it for much higher and then lowered the price apparently due to him messing the jack up while cleaning it up for a buyer. That being said, I can’t prove this isn’t stemming from an issue. When I opened the unit up everything was clean internally and nothing looked glaringly messed up with the jack.

I looked at the service manual and while its a bit tough for me to understand what’s going on, I can identify an amplifier chip that sums the signals for the main output. I figure it would be worth checking on that part. Is that as simple as just clipping a multimeter to it and seeing if voltage is going to it/coming out of it? Apologies if this is kind of an elementary question!

You would need an oscilloscope to see the audio signal going in and out to verify the chip is working. Multimeters are good for testing DC signals mostly. However, with your multimeter you can do some continuity testing to make sure traces and solder joints are good between that last components and the jack.

The jack itself probably couldn’t have been damaged from contact cleaner. But if the previous owner says that’s when the issue began, then he may have sprayed the contact cleaner while the device was powered on, shorting a component and causing it to fail. There’s a good chance it could be the last IC if it’s near the jack but hard to say for sure without an oscilloscope. Looks to be a 1458, we have them available on the website.

It could be a component before this in the signal path too, so check with an oscilloscope if you can. Feel free to ask any questions, nothing is ever too elementary.

In regards to the mysterious cleaner spray, use a 70% 99% alcohol (usually available at grocery stores or pharmacies) to wash and remove whatever the spray was. The switches pull apart If I remember so you can clean inside with a alcohol dipped q-tip.

As for using an oscilloscopes, even the cheap ones on ebay will work with audio signals. once you have one, you’ll never look back, they open a new world of curiosity.

Since many people here are novices,

having a battery powered scope is much safer than working with a mains powered scope. If you don’t use an isolation transformer with the scope, you can accidentally discharge your synths power supply through the scope, blowing it up. Electricity is always trying to find the easiest path to ground, and with faulty equipment, electricity is not always where you think it may be.

With battery powered scopes that doesn’t happen.

I’m a little bit confused for some reason with how replies work on this thread sorry.

But essentially the issue is with the jack, so would I want to dip a q tip in alcohol and lightly swab out the jack? Also I hear complete silence when plugging in instead of the usual quiet noise floor with all the other outs. Does that imply dead or dirty?

I replied the same thing to another post, but I’m getting complete silence from the jack instead of the usual quiet noise floor with all the other ones. Does this imply dead or dirty?

Also, could you recommend any simple small oscilloscopes or is it generally an anything will do kind of thing? There’s a few cheap chinese handheld scope/component tester combos in the classifieds around me. Going off of the other commenters recommendation for something battery powered, would something like this be ok? Or would I want something with more accuracy.

And are guides for testing audio circuits pretty available or could you point me towards some good resources?

Thanks so much for your help.

The jack being completely silent might imply it being dirty if the plug isn’t making electrical contact with the jack. But usually after a few times of plugging and unplugging you would at least get some signal out of a dirty jack. It could also be the jack’s solder joint and it just needs a reflow or new solder. You would be able to tell by inspecting the board from the bottom. Look and see if the solder joint looks cracked, lumpy, or particularly lackluster. On the other hand, often when Opamps fail their output gets stuck at V+ and they pass no signal. I’d still suspect some noise floor in that scenario but hard to say for sure.

For an oscilloscope, most should do. You usually don’t need to take many precise measurements for synth repair, the oscilloscope is more to see if any signal is there or not.

There’s lots of great advice for electronics repair on Youtube scattered about. Synthchaser does great videos and explains his reasoning and methods but he’s got a ton of videos so it can be hard to find the info you need. Knowing your components helps with making educated guesses about what has malfunctioned but most of the time working on old equipment is a matter of replacing transistors, ICs and electrolytic capacitors.

Any questions, feel free to ask.

No signal on a jack means you have to open the unit and look for reasons why there is no signal, either dirt, mechanical failure, or solder connections on the jack, or wiring to the jack is faulty or broken.

Have a look at this scope. Its all you need for just audio signal finding. it’s 200khz so won’t detect clock crystal signals. its also limited on power supply use.

for not much more money, A 25mhz scope like this will find most clock signals, and will work on power supplies. I haven’t tried it, but it should be good enough for troubleshooting.

Great thanks, I’m away from the unit at the moment but will inspect the board this week to look for faults or anything obviously broken. I’ll also try plugging and unplugging the jack a bit and perhaps going in a bit more seriously with a q tip.

If that doesn’t go anywhere I’ll do some youtube viewing to check out how to use the scope and all that. Of course, if that goes nowhere I’ll probably be back here haha.

Ended up going with a Hanmatek handheld scope I found in the classifieds, seemed pretty nice! Glad to know most scopes will do though.

Thanks for all your help!

Great thank you! I went with a hanmatek scope I found on marketplace, might be a bit overkill now that I’m looking at these but seemed good to me and wasn’t terribly priced.