Marantz 1060 - Can't set bias, output cap overvoltage

[jtmpspm]

Hi

I have recapped my 1060 and powered up to set the bias but I am seeing C006 (Nichion 6800uF 63v) go to ~70v. Adjusting the R723 makes no difference. I have checked that the pots are all working.

The other channel is at a reasonable level.

Have any of you come across this before or able suggest where I should be looking to fix this? I am worried about powering it up to test too as it is above the rating for the output capacitor!

Thanks

 

[tranguru]

Hi

Are you sure the line voltage is OK?

 

[jtmpspm]

Yes the C003 capacitor is at 80v, checked at J709. I think I will replace all the transistors and see if that makes a difference.

 

[Steven Tate]

I would start pulling transistors and testing, starting with the outputs and working back. If they test good, you can put them back in. When you start seeing rail voltage where it shouldn't be, there are likely one or more bad components on the board. Test transistors, then diodes, then resistors. Of course triple check polarity on any components you changed, and look at the bottom of the board with magnification to make sure there are no solder bridges, cold solder joints or cracked traces.

 

[jtmpspm]

I found the issue to be R717, was blown open such that the R723 trimmer pot was out of circuit. Now time to put everything back together

 

[tonebells]

Tony

 

[Metal L]

H

I found the issue to be R717, was blown open such that the R723 trimmer pot was out of circuit. Now time to put everything back together

Hey! Did this end up solving the problem or were there any other issues at play? I have a 1060 that had a blown a fuse when I had received it. Found a bad output transistor and 1 bad middle transistor, along with a couple resistors.. I replaced both pairs and the resistors but I cannot for the life of me get this thing to go back into its idle current spec. It can adjust, but not low enough for stable operation... Edit: I have tried replacing the bias/idle current pot with a decent multiturn pot and it does not make any difference. my MJ21196G's for H003 and H004 are getting hot in very short order and I cannot get the voltage across R748 to go lower than about 250mVdc whereas the other channel is at around 18mVdc across R747

 

[catrafter]

See my sig line.
Sigh.

Tom

 

[Steven Tate]

I have learned my lesson from Catrafter after tracing down several amp problems. All of those voltages on the schematic depend on every component working properly. If one fails, or you introduce a short somewhere, voltages will go crazy all over the board, and measuring them doesn't give much of a clue where the problem is. In the absence of an 'octopus' or Huntron Tracker, it boils down to a tedious search for shorts, solder bridges, cold solder joints, failed transistors, diodes, resistors (in that order IMO). Personally, I haven't found many caps to be causing catastrophic problems unless I installed them backward or they physically looked blown up.

 

[EastPoint]

H

Hey! Did this end up solving the problem or were there any other issues at play? I have a 1060 that had a blown a fuse when I had received it. Found a bad output transistor and 1 bad middle transistor, along with a couple resistors.. I replaced both pairs and the resistors but I cannot for the life of me get this thing to go back into its idle current spec. It can adjust, but not low enough for stable operation... Edit: I have tried replacing the bias/idle current pot with a decent multiturn pot and it does not make any difference. my MJ21196G's for H003 and H004 are getting hot in very short order and I cannot get the voltage across R748 to go lower than about 250mVdc whereas the other channel is at around 18mVdc across R747

Start a new thread and we’ll go from there.

 

[Metal L]

Start a new thread and we’ll go from there.

I realized I made a mistake with one of my transistor subs. New parts on order. If this does not solve the issue then I will begin a new thread.
Thanks for the suggestions everyone!