700/1 “Tim” WOPL driver board

Floyd Loonie said:
Very nice job! How did the unit work after the effort and time? I asked around about WOPL for my PL700/1 that is stuck in protection circuit mode, and the replies I received were overwhelming for the "don't waste your time & money/not worth doing" side of the opinion poll! Ican understand the OG 700/1 is kind of a red-ish tinted dred lock lookin' step child, but I had that amp for many years & it was reliable and was 50 years old when it finally quit working... Lots of HiFi amps stop working long before that age!! I don't have the training,skill, or any of the necessary test equipmet needed to fix the unit. But I have not given up on finding a way to put it back in service playing music for someone else to enjoy. I enjoyed reading your comments that were posted as you put that board together. THANK YOU!!
Click to expand...
It’s worked great other than issues I caused or am still chasing as I’m a relative n00b to this stuff... overall I would say the 700/1 is very worthy of repair. Keep in mind mine is not a full WOPL conversion so the original backplanes are still in play. The new driver board solved idle noise and DC offset issues of the original amp, I’m having an intermittent bias issue with the right channel which I believe is going to turn out to be a bad output transistor socket, I’m currently removing the right channel back plane to clean/inspect/swap sockets from my WOPL’d 400.

If you can solder and have a multimeter, with all the help and guidance available here I have no doubt you can fix yours yourself. It’s been a great learning experience for me and it’s relaxing way to kill a rainy day. Don’t feel bad if you make mistakes, I blew Tim up twice a couple days ago on the work bench, second time there was fire! Also I believe the parts are available to fully WOPL the 700/1 now also if you choose to go that way you can buy the boards assembled then it’s nearly plug and play with some fairly easy testing during bring up.

so this morning I’m disassembling Tim. Going to completely remove the right side back plane, inspect the sockets and test all the semi conductors. I had an intermittent issue of bias running high during bring up most often when installed the second row of outputs. That rows tranny sockets look to have been over tightened at some point so hopefully there’s an issue there. I smoked the bias resistors the other day too, whatever the issue is it caused over 12vdc bias and in short order lit them 1/4 watt resistors on fire... I think I’m going to install Linda’s Phoenix connectors on Tim’s board and order more, I was too optimistic that I probably wouldn’t have to remove the driver board, desoldering wasn’t a big deal but then connectors would sure make things easier.
 

Attachments

  • 98F95647-C733-4DF2-9CDC-85C00BAA41A9.jpeg
    98F95647-C733-4DF2-9CDC-85C00BAA41A9.jpeg
    3.8 MB · Views: 10
What a mess of old thermal paste behind there... might as well pull the left channel too and give everything a real good cleaning...
 

Attachments

  • A1FCFEBB-D64C-4C15-9EA1-2854F6013DC0.jpeg
    A1FCFEBB-D64C-4C15-9EA1-2854F6013DC0.jpeg
    4.1 MB · Views: 12
Careful on those bias trannies wires. They are extremely brittle. Do the diode check on those before you solder them back in..
The deadly white grease. If you have some oilfield buddies, get some condensate, spray it on and it runs off..EXTREMELY FLAMMABLE though...
 
Bias trannys check out, pretty well matched too. Also checked the emitter resistors and diodes, all checks good. The bias resistors are both dickered. Other than the thermal paste the sockets look ok, funny thing is when you tighten the second row is when the bias would go wonky leading me to believe there’s a localized problem there. Didn’t matter if you swapped output trannys, same result.
 

Attachments

  • E7164125-74D3-4C1F-B843-62965B490F51.jpeg
    E7164125-74D3-4C1F-B843-62965B490F51.jpeg
    3.5 MB · Views: 5
Skratch said:
I've been using the MJF31CG for bias transistors, track very well and are very rugged
Click to expand...
I don’t remember what these are and they’re in the P straps now. Lee sent them along with the WOPL parts way back when.
 
Looking at pulling the bias resistors from Linda’s pre WOPL guts. They’re mismatched, and measure 13 ohm for three of them but the color code doesn’t workout or I’m reading it wrong. Brown, black, black, silver, gold works out to 1ohm 100x.01 5%??? Tim’s are 10 ohm, brown, black, black, gold. I got some new resistors coming tomorrow, doubt I’ll get far enough along today to really need them.
 
Have you considered replacing those original caps on the backplane? I'd be concerned they could be bad. Probably not the bias problem though.
 
Vynuladikt said:
Have you considered replacing those original caps on the backplane? I'd be concerned they could be bad. Probably not the bias problem though.
Click to expand...
Yeah I just took them out of circuit and tested them. They’re 4uf and testing at 9uf, one has a a couple ohm ESR the other under 1 ohm.
 
Got things cleaned up a little better... man that stuff gets in everywhere... not seeing anything obvious with the sockets except it looks like paste has got between the two layers of the sockets...
 

Attachments

  • 7528AF11-A3B8-4040-843C-339DDC3FC8F7.jpeg
    7528AF11-A3B8-4040-843C-339DDC3FC8F7.jpeg
    3.6 MB · Views: 8
How critical are them caps to ground on the back plane? I can’t get non polarized caps easy today but I can get 8uf non polarized and put a pair in series. Thoughts?
 
Linda’s are all broken except for two or three so not much good parts there. Got 1/2 watt 10 ohm carbon resistors coming, that’s I’ll work for the bias circuit eh? How about them caps?
 
stetter said:
Just asking , How come you don't finish upgrading with new WO Backplane kit ?
Click to expand...
Until recently the backplanes would not fit a 700/1. I believe there’s a new chassis and best sinks available to accept 700/b back planes. I’ve also had a very generous offer of free full complimentary back planes from a 700 pro. They might take a little modification to fit but there going to be on their way towards me soon!
 
OK now I know the rest of the story, I assume you are like me then and just want to make the broken gear work again just for the experience.
 
stetter said:
OK now I know the rest of the story, I assume you are like me then and just want to make the broken gear work again just for the experience.
Click to expand...
Yep, I’d be fine with the quasi-comp if it works as it should. The WO driver board solved many problems but I got some gremlins left over from the old back planes. I’ll probably try and get it working next few days, then tear it apart when the 700 pro bits arrive.
 
You must log in or register to reply here.
Back
Top