Roland Studio 6V troubleshooting question

[Garydean]

I'm working on an early 80's Roland Studio 6V combo. First I must say this thing is a trip to work on.... The first issue is the flanger, activate it and it blows the fuse. I figure the 16 pin SAD1024 might be shot. It's socketed unlike the rest of the components on the board, so someone has been in there before me. I can't locate another one. I saw a few on ebay that had closed for $26 shipped. The thing I'm concerned about is perhaps it's bad due to a bad support component. At $26 a pop I can't afford to shotgun this thing.

The knobs are pressed onto the shafts to a point beyond removal without damage. Someone previously has attempted to remove a few (2) and had destroyed the skirts. Another sign of this issue is someone had replaced several transistors by snipping them out and soldering replacements to the remaining leads. Resistors have been snipped, tested and re-soldered.

Another issue is low output. There are 6 - 6L6 output tubes. The first 3 tubes have connecting plates that run to the OT high. The last 3 tubes have plates connected to the OT low. Not sure I get what is going on there.

Last, but I'm sure not least, there was also a complaint that the speaker chirped at certain power chords. This could be a bias problem or severely mismatched tubes....true?

Where do I begin troubleshooting this freak?

Thanks,
Gary

[52 Bill]

I hate getting stuff that someone who is unqualified has worked on before. You usually have to spend half the repair time finding and fixing things that should not have been done before.

Pull the SAD chip out and see if the fuse blows. There has to be a power supply short in there somewhere, but it could be anywhere in the flanger circuit. The SAD chip is static sensitive so use proper grounding procedure to pull and store the chip.

If you can't pull off the knobs, tell the owner that in order to fix it you'll have to cut them off and replace them with something that will look nice. It's not really cost effective to spend tech time on pulling knobs. Maybe the owner would prefer to pull the knobs himself.

Fixing from above the board is the way that some techs work all the time, as a time saving method. It will work sometimes, but often it will cause the solder joints below the board to become cold from being improperly re-heated. I would suggest pulling the board out and fixing all of these before returning the repaired unit as they may come back to haunt you.

[Garydean]

Thanks for the solid advise and support Bill.

Gary