> And Gordon, I do understand what you are saying about test first, then replace. However, I do NOT own an oscilloscope, and the factory service manual is only schematics, no test procedures for the various ICs. I've been using the schematics supplied by Michael Buchner to me that are far superior to the factory ones and this has been a major
Okay, you really do need to get an oscilloscope. They're not expensive. Pick up a dual-trace analogue 'scope from someone who will allow you to go along to pick it up in person, and get them to show you it working.
This will make everything easier. Working without the basic test equipment (even just a good meter and 'scope) is a bit like a heart surgeon saying "well I don't have a chest saw so I just chop my way in with a fire axe"...
Testing the chips is merely a matter of making an educated guess at how the output is going to look given the input. It's worth considering that the 4051s and accompanying TL084s are acting as a unit to form a multiplexer and sample-and-hold - so compare the input of the MUX with the output of the buffer, first.
> asset. I am NOT a professional electronics repair tech by any means, but I do have a basic understanding of what the various electronic components are supposed to do and have limited schematics reading ability. Fortunately my soldering skills are much better than my "diagnosing" skills. This is why I've been asking advice here to
help point me in the right direction. It may seem to some that I'm
I do tend to cast a suspicious eye over 405x MUXes and their buffer amps ∗but I test them first∗ ;-)
> just randomly replacing parts, but I am going on the theory that these components are nearly 30 years old and are near the end, if not already at, the end of their life and should be replaced anyway in order to make it function correctly again. I have been going in
They don't really wear out, although they do fail. Some synths seem to be worse than others in this regard, possibly due to design factors.
> stages as suggested by others here, and as it is, I'm having progress. Limited as it may be, but it is still progress. I am closer to it being fixed more tonight, than any time in the past. Recapping it helped the sound AFTER I replaced the mux/demux 4051 ICs and IC61. The sound quality is even better after replacing the mux/demux tl084 ICs, and it has resolved a couple of the issues I was having, but not all.
Again, you could save yourself a lot of time and money with the proper tools. Pick up a 'scope for £50 or so, and it will save you so much bother. Bear in mind you don't necessarily need it to be accurately calibrated - you're mostly looking for qualitative rather than quantitative measurement, ie. "Is this actually a square wave?" rather than "Is this exactly 4.75V peak-to-peak?". The former kind of question crops up in diagnostics all the time, the latter almost never...
> Again, thanks to those who have helped here by steering me in the right direction, especially Michael for the great schematics and advice.
It sounds like you're making good progress, but seriously - buy a 'scope. And once you've done that, you get to work out how to get at the bits of the board in the middle of a stack ;-)
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Gordonjcp MM0YEQ