Vintage Synth Repair

Magnus, 

You did no harm, those pins are easy to mis-align when lowing the upper tray.  They are for the audio.  Auto tune uses the audio output of each voice card to calculate tuning.

I think that you have a problem on #5 as you stated.  You can remove #5 and swap it with another known good location. If it works in some other location correctly then I would look for the issue in the mother board or on the CPU.  The OB8 did not have the problems that the earlier OBX and OBXa exhibited with cold or cracked solder connections on the voice card mother boards.  OBX and OBXa often need every connection re-done before trying to calibrate or tune. 

So move #5 to known good slot and re-test.  Trouble moves, trouble on that voice card.  Then you can look for what is the actual problem, VCO chip, buffer, cap or connections.

R



>________________________________
> From: Magnus Arni Oder Kristinsson <magnusarnioder@...>
>To: vintagesynthrepair@yahoogroups.com 
>Sent: Tuesday, March 5, 2013 4:10 PM
>Subject: [vintagesynthrepair] Oberheim OB8 tracking problem + more
> 
>
>  
>Hi and thank you for giving me access to this group!
>This is my first post here and the the main reason I found out about this group and asked to join in.
>
>
>Sorry how long the post is but I thought would be best to give you the whole story.
>
>
>If anyone has any knowledge that could help, please share the love!!
>When I got the OB8 it worked well (all voices tuned up) but I found one thing that was wrong. When I put it in split or double mode the two patches (oscillator boards) went out of tune to each other.
>I decided to try the calibration process before getting in to changing the capacitors which I had read on the internet is often the reason for problems in obxa and ob8.
>
>I decided to go through the calibration.
>The calibration went smoothly but I did one mistake. When I had been working on the lower board and put the top board in plaice again the pin on the connectors between the two boards did not go correctly together. I did not notice this until after I had turned the synth on and they instrument sounded strange. Than I turned it of an on again and I think I remember correctly everything worked for some time (might not have). Than I finished the calibration and voice number 5 started to act strangely. I attached picture of the connector and how I put it wrong together. I don't think this did anything because I think these connectors are just the outputs on the upper osc board to the lower osc board.
>
>https://dl.dropbox.com/u/8442294/OB8%20in%20Iceland.JPG
>
>Problem number 1. Oscillator 2 on Voice nr. 2 could not be tuned with the volts per octave trimer and is little bit out of tune now (all voices tuned with the auto tune before calibration). The voice is not to much out of tune so I am not worried about this at the moment.
>
>Problem number 2. Voice nr. 5 could be tuned with the volts per octave trimer (booth osc 1 and osc 2). But when played after calibration osc 2 on voice nr 5. does not track correct (osc 1 on voice nr5 is perfect). Both osc track perfectly until D#4 (the D# on the fourth octave on the OB8 keyboard) on the synt and than it goes its own way. If I change octaves with the transpose button the problem moves accordingly. So if I transpose one octave down osc2 on voice nr. 5 plays correctly untill D#3 and if I transpose one octave up it plays correctly till D#5. 
>That is why I think the problem is not on the voice boards but with the informations that is sent to the voice boards.
>I attached a sound sample so you can listen.
>I play the white notes on the keyboard from lowest to higest. I turned off all voices except nr. 5.
>First part is osc 1 only
>Second part is osc 2 only
>Third part is osc 1 and 2 played together
>
>https://dl.dropbox.com/u/8442294/Voice%205%20OB8.mp3
>
>Recently voice nr. 6 also started to behave like voice nr. 5 but the problem is with osc 1. The problem on voice nr. 6 comes and goes.
>
>Problem number 3 In split or double mode the lower patch selected sounds strange.
>Here is a sound sample of me playing the same part with the same sound on both upper and lower board in split mode. 
>First I play the upper and than the same thing on the lower.
>
>https://dl.dropbox.com/u/8442294/Split%20mode%20OB8.mp3
>
>I have the feeling that the problem is in some digital controll but not on the voiceboards. I draw this conclusion from the fact that if I transpose an octave up or down the problem moves accordingly with the transpose and is exactly the same but just an octave lover or higher.
>
>I have changed all the electrolytic caps on the synth. 
>
>If anyone can please help me with this, I will be so grateful!
>I live in Iceland and we don't have any synth techs here so I have to figure this out myself or ship it oversees (would probably cost half of the synths price + repair).
>
>Thanks in advance!! 
> 
>
>