new board member - Trace Elliot preamp problems

[chris1127]

Hi, just joined the board so thought I would say hi. Been playing guitar and bass for a few years now; always repaired my own gear and learnt a bit along the way but seem to have loads of projects on the go at the moment so thought i would join up. Been spending quite a bit of time trying to plexi-fy my Laney AOR30 recently (tamind the fizzyness mainly and tightening up the bass), as well as playing around with the boost and tone stacks in a freinds Peavey C30. As well as that I am trying to "clone" a 60s Triumph Leo 7w valve amp in a turretboard layout.

I'm also midway through trying to repair my Trace Elliot gp12smx preamp at the moment after switching it on with the voltage selector knocked from 240 to 115v it's mainly up and running but problems with hum in the graphic circuit, and the compressor doesn't seem to be working. I've re-capped the back board on the amp (surge took out all the 35v electro caps) and replaced the varistor so far, and having read the service manual on here am going to try replacing IC5 (on order) which seems to be used in both the graphic and the compressor. Anything else obvious I should be looking at after torturing it with far too many volts?

[Enzo]

No, just keep plugging away at it. When twice the normal voltage went through the circuits, your caps exceeded their ratings, but probably so did the op amps and other semiconductors.

And if there were failure currents, look closely at the boards for any burnt-open copper traces. A trace can burn open like a fuse under excess current, generally at a narrow spot. An open ground to part of a circuit could cause hum and lack if function.

Check that all voltage regulation is OK. You may replace some filter caps, but for example if there was a zener regulated drop from a higher voltage rail, that zener may be bad and the circuits it serves are no longer getting clean power. For that matter even a three-leg Vreg IC could have failed. SO check the +/-12 or +/-15 or whatever that model runs on for clean and proper voltage

[chris1127]

Thanks for the reply/tips Enzo, I've ordered a few IC's now (5 are the same part number and they are sold in batches of 5 which works well), theres' a handfull of diodes on the board so will check through them too. There's no obvious sign of damage to any traces on the board but will take a good look under an eyepiece later. It's an 18-0-18 pt with a 150v upper for the HT on the valve so will check voltages around the board too.