Vintage Synth Repair

You're certainly off to an excellent start, you have schematics, such as they are, and a good oscillator to do direct comparisons with. The tool I've found most helpful is an oscilloscope. If you don't have one already, you can always get a used one really cheap.  I recommend starting somewhere where it is working (maybe the signal coming off the keyboard for example ), then tracing it to where one of the oscillators begins to  do something different than the other. That's where it is failing. What it all boils dow n to is that s ooner or later, somebody is going to have to do all  the troubleshooting right there at the instrument . Since I am separated by the internet , I can only make guesses and vague generalizations.

----- Original Message -----
From: salsole@...
To: vintagesynthrepair@yahoogroups.com
Sent: Monday, December 9, 2013 9:11:52 AM
Subject: [vintagesynthrepair] ARP Solus OSC1 tracking issue. ..

 




Hello all... I don't know whether the last message I sent made it through or not... Anyhow. I am working on an ARP Solus that had a dead VCO1. I replaced the tempco resistors, (r60 and r98) and it fires up and sounds great. Now the issue I am having is that VCO1 tracks in reverse, and badly at that. VCO2 is tracking perfectly. The service manual and schematics available are pretty poor in quality and somewhat topical in nature. Anyone have any suggestions about where to look? Thanks much

So reachable through the front panel are:



VC01 V/oct = R62 on the top of the vco section by the line on the right

VC01 Initial Frequency =R56 above the first of two sliders front panel in the VCO section and to the left lower is the pulse width for VCO1 (not an issue)



TP2 low C key is 1V DC current Hi C 1.8V DC

TP3 low C .1 V dc high c= -2.7VDC

Now if they are messed up I wonder about that 4558 IC that both share. (top of p 7 of schematic



TP10 -5V DC

Power supply, Dangerous 120V!

TP 14 +15V DC

TP 15 -15VDC  adjust for both is R213





Calibration VCO 1

step 0 check voltages from Power supply

step 1 Calibate keyboard, monitor cv out low C then high C should be exactly 3.0 V apart adjusted by keyboard trimmer.

step 2 set pitch bend knob, pin low Cat centre of knob go hard right shoukld have 1 V for 1 octave range

step 3 with vco 1 transpose should be 1 octave/1 volt

step 4 transpose normal, pitch bend centre, pin low C, centre master tune slider, VCO Cal adjust to C

step 5 vco1 V/Oct, both trimmers interact, go to Volt oct trimmer, then back to cal trimmer, then repeat as you get closer.  I use a plastic screwdriver to avoid grounding issues mucking with it and setting it warbling off again.  back and forth till you have 3 octaves/3 volt low to hi C, get close, start again, get closer, etc.



Now you may have done all this.  If so, this is an odyessy thought: are you really sure your power connector is not reversed if it has three coloured wires ie a -V is feeding a +V pin.  On the ody they just push on with ground in the centre, its easy to reverse them by accident.  A reversal may still make sound.  But it looks like a single board and teh schematic says zip about connectors, but it sounds like that kind of problem.



Lorne in Canada

From: vintagesynthrepair@yahoogroups.com [mailto:vintagesynthrepair@yahoogroups.com] On Behalf Of kslinkard@...
Sent: December-12-13 2:27 PM
To: vintagesynthrepair@yahoogroups.com
Subject: Re: [vintagesynthrepair] ARP Solus OSC1 tracking issue. ..





You're certainly off to an excellent start, you have schematics, such as they are, and a good oscillator to do direct comparisons with. The tool I've found most helpful is an oscilloscope. If you don't have one already, you can always get a used one really cheap. I recommend starting somewhere where it is working (maybe the signal coming off the keyboard for example), then tracing it to where one of the oscillators begins to do something different than the other. That's where it is failing. What it all boils down to is that sooner or later, somebody is going to have to do all the troubleshooting right there at the instrument. Since I am separated by the internet, I can only make guesses and vague generalizations.

  _____

From: salsole@...
To: vintagesynthrepair@yahoogroups.com
Sent: Monday, December 9, 2013 9:11:52 AM
Subject: [vintagesynthrepair] ARP Solus OSC1 tracking issue. ..



Hello all... I don't know whether the last message I sent made it through or not... Anyhow. I am working on an ARP Solus that had a dead VCO1. I replaced the tempco resistors, (r60 and r98) and it fires up and sounds great. Now the issue I am having is that VCO1 tracks in reverse, and badly at that. VCO2 is tracking perfectly. The service manual and schematics available are pretty poor in quality and somewhat topical in nature. Anyone have any suggestions about where to look? Thanks much

When I worked on a solus some time ago I recall a bunch of bad 1458 op amps. Also, some chip or part that got quite hot & popped when the tempco resistor was bad. No schematic in front of me now. Hope this helps!
Hugh

It was the 1458 that VCO1 and VCO2 share. Half of it was bad... thanks for the help fellas!!