700/1 “Tim” WOPL driver board

[AngrySailor]

Hmmm she’s acting up on me... right channel again. Got three rows of outputs in then the bais jumped to ~600mV and the bulb came on dim. Seems if you fiddle with the output retaining bolts on the (from inside the amp) left row of the right channel the bias will jump from 220-600mV. Stripped it right down to drivers only and she went back to the 20-30V bias right channel. I pulled a pair of RCA410’s from Linda and swapped them in and she went back to 220mV with no outputs. Put the first row in and back to a dim bulb and 600mV bias right channel. These are new 2SD555 outputs and I swapped a few different ones in.

I’ve been looking at the back plane real close, moved a few emoter resistors away from screws, generally looking for anything that could be a problem. There’s a diode from the collector bus bar to the emoter resistors that looks like it’s been hot but other than that not seeing anything wrong.

Any suggestions? Was going to try soldering in the drivers on that channel and if that solves it I’ll gut Linda for tranny sockets as she’s getting White Oak back planes...

 

[George S.]

Hard to say with a intermittent, but, you pointed out a diode that looked cooked, that could be it. Intermittent connections usually heat up due to high resistance. If everything mechanical ohms out good and looks good, then I'd be looking at semi conductors like that suspect diode. You might want to try thermal stressing various areas of the back plane with hot air to see if it makes a difference, but a crispy diode may be the issue or something in circuit with it.
Just make sure your not grounding out those outputs when you install them. The case and screws need to float above ground. When I tore down my two 400s, there were several damaged sockets, some of those self tapping screws were very close to grounding on the case. Later.

 

[AngrySailor]

Hard to say with a intermittent, but, you pointed out a diode that looked cooked, that could be it. Intermittent connections usually heat up due to high resistance. If everything mechanical ohms out good and looks good, then I'd be looking at semi conductors like that suspect diode. You might want to try thermal stressing various areas of the back plane with hot air to see if it makes a difference, but a crispy diode may be the issue or something in circuit with it.
Just make sure your not grounding out those outputs when you install them. The case and screws need to float above ground. When I tore down my two 400s, there were several damaged sockets, some of those self tapping screws were very close to grounding on the case. Later.

Yep I was looking at the sockets and checked all the silpads as I was removing/replacing outputs. One socket looks a little crushed from over tightening but it’s not touching ground. Ohmed out the transistor cases to ground, they all check out as not shorted. It seems to keep coming back to the driver sockets on the right side, think I might first try tinning the pins on the drive trannys to beef them up a bit tighter in the socket. I can rob Linda for those diodes also if I figure out which sockets are bad Linda can supply them also.

 

[George S.]

Probably just old sockets filled with heat sink compound.

 

[George S.]

Like having a yard full of parts cars!

 

[laatsch55]

For outputs?

 

[AngrySailor]

There was a metric fuck ton of heat sink compound on this thing... maybe some small pipe cleaners might help clean them sockets?

 

[laatsch55]

Yep, welcome to the world of intermittents.

 

[AngrySailor]

Got my marine medical done, the folks want to explore the “big city” for a couple stops then I’ll be back home try and sort this out. The bastard should be making music soon.

 

[laatsch55]

Yeppers...

 

[Gepetto]

Hmmm she’s acting up on me... right channel again. Got three rows of outputs in then the bais jumped to ~600mV and the bulb came on dim. Seems if you fiddle with the output retaining bolts on the (from inside the amp) left row of the right channel the bias will jump from 220-600mV. Stripped it right down to drivers only and she went back to the 20-30V bias right channel. I pulled a pair of RCA410’s from Linda and swapped them in and she went back to 220mV with no outputs. Put the first row in and back to a dim bulb and 600mV bias right channel. These are new 2SD555 outputs and I swapped a few different ones in.

I’ve been looking at the back plane real close, moved a few emoter resistors away from screws, generally looking for anything that could be a problem. There’s a diode from the collector bus bar to the emoter resistors that looks like it’s been hot but other than that not seeing anything wrong.

Any suggestions? Was going to try soldering in the drivers on that channel and if that solves it I’ll gut Linda for tranny sockets as she’s getting White Oak back planes...

2SD555???

 

[AngrySailor]

2SD555???

Yes with RCA410 drivers

 

[George S.]

Andrew, if your sure the sockets are the issue, and since your rebuilding it basically with only the control board being new, maybe consider soldering those connections. In the future you can always go back in and rewire it Full Complimentary with new sockets and the latest best outputs. Would make a great winter project for the future and maybe you'd have better tools by then like a nice vacuum desoldering station for making the changes on the control board. In any case those outputs should drop out with a decent size magnet and two soldering irons. Seems the easiest way to go.

 

[AngrySailor]

Andrew, if your sure the sockets are the issue, and since your rebuilding it basically with only the control board being new, maybe consider soldering those connections. In the future you can always go back in and rewire it Full Complimentary with new sockets and the latest best outputs. Would make a great winter project for the future and maybe you'd have better tools by then like a nice vacuum desoldering station for making the changes on the control board. In any case those outputs should drop out with a decent size magnet and two soldering irons. Seems the easiest way to go.

I was going to try cleaning them first with alcohol and pipe cleaners. There was a shit ton of heat paste and I scrubbed and used compressed air to get rid of it. Some surely went into the socket holes. Failing that I’m going start getting caveman on the right channel Q11&12

busy getting ready to spray epoxy primer on some tractor parts rn though.

 

[George S.]

Good idea, I use alcohol for getting old compound off CPUs and other chips. Works good.

 

[AngrySailor]

Got that over with...

 

[AngrySailor]

Think I got it licked. The problem with the bias rising from ~230mV to +600mV happened when I snugged the outputs. Pulled the sockets away from the back plane slightly and sprayed some cleaner between them. There was lots of heat paste between there. Right channel was giving me trouble now has all rows of outputs installed, 100w bulb is right out and bias is at 220mV with the bias pot at minimum.

 

[George S.]

Have to wonder if some of that paste is conductive. Glad you got it solved and hope it stays stabil.

 

[AngrySailor]

All outputs in, bias set to 350mV both channels, DC offset 0v both channels.

 

[AngrySailor]

Yeah almost seems like that paste was conducive. The more you snugged an output the higher the bias would rise. Blew them all out again and she’s sitting here idle with all outputs installed. Time to loose the dim bulb I guess and do final settings.