Resurrected a Customized WOPL 400

When the red bias wire burned thru on mine right at the backplane solder connection, I had the first row of outputs in and was slowly bringing the voltage up on the variac and watching the DBT. I was nervous as could be. When that arc flashed I was already turning the variac all the way down as I heard the pop or snap of the arc. Luckilly all I found was a blown pico fuse after ohming out the board. I replaced it and the resoldered the wire. The rest of the build of the two 400s was uneventful, you betcha I followed Joe's written instructions precisely. But, that arc issue really nagged at me. So I ordered more screw terminal blocks for the backplanes to complement those Joe sent me for the control board. Both amps turned out wonderful, both have .000v offset on the left channel, .001v on the right, bias dialed right in evenly at .35v on all channels with the pots at identical clock positions. So, keep at it, these guys will help you get it fixed. Most amazing thing to me about a WOPL is I no longer have to turn the volume up high to hear the music detail, it's there at reasonable sound volumes, great for old guy like me.
 
Yeah, now it's time to order parts. And I have a drawer full of plastic washers. So I'm sure I can resecure the boards without any risk of shorting. The back of the boards are trimmed very close, less than 1/16", probably closer to 1/32" on the highest solder joints. Also, does that parts list look okay to anyone?
 
scottonnob said:
Yeah, now it's time to order parts. And I have a drawer full of plastic washers. So I'm sure I can resecure the boards without any risk of shorting. The back of the boards are trimmed very close, less than 1/16", probably closer to 1/32" on the highest solder joints. Also, does that parts list look okay to anyone?
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Hi Scott
You probably damaged a few semiconductors too so should check all outputs and the transistors in locations Q7L and Q8L. With the damage done to R24L, I would be surprised if Q7 survived that.
 
Gepetto said:
Hi Scott
You probably damaged a few semiconductors too so should check all outputs and the transistors in locations Q7L and Q8L. With the damage done to R24L, I would be surprised if Q7 survived that.
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You don't get support like this ANYWHERE else.
 
Isn't that covered by the Dark Lady Sonnets, #127–154, regarding failed connections?
 
Both Q7L and Q8L appear to be blown. At least that's what my DMM is showing with them in circuit. Since I have to pull the board anyway, I'll remove 7 and 8, and test them out of the circuit, just for curiosity. Of course, I'm going to replace them as well. I have a few 651s. I'll have to order 751s. The list is getting longer.
 
scottonnob said:
Both Q7L and Q8L appear to be blown. At least that's what my DMM is showing with them in circuit. Since I have to pull the board anyway, I'll remove 7 and 8, and test them out of the circuit, just for curiosity. Of course, I'm going to replace them as well. I have a few 651s. I'll have to order 751s. The list is getting longer.
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Check your output transistors. I would be surprised if you did not blow any.
 
I'm just going to replace all the important parts. It doesn't cost that much to do so, and then I'll feel more confident when I bring it up again.
 
Resurrected amp project. Half way there. Powers up fine. Relay clicks. Left channel has good bias and puts out great sound when connected to source. Right channel almost dead. A very faint crackling sound, like a bad connection, but no volume to speak of. No/zero voltage at bias check point. All resistors and fuses check good. Voltages good a +-15. Checked all connections. Don’t know what else to check. This is not the channel that was blown. P.S.: Sorted out my 3300 problem. Will post findings.
 
So this amp has not worked correctly since you built it? It's been a couple years since you worked on it. The right channel WAS working and the left was blown? Now the opposite???
 
Send pics of what you have Scott and we will work you through this....
 
scottonnob said:
Resurrected amp project. Half way there. Powers up fine. Relay clicks. Left channel has good bias and puts out great sound when connected to source. Right channel almost dead. A very faint crackling sound, like a bad connection, but no volume to speak of. No/zero voltage at bias check point. All resistors and fuses check good. Voltages good a +-15. Checked all connections. Don’t know what else to check. This is not the channel that was blown. P.S.: Sorted out my 3300 problem. Will post findings.
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Send pics Scott, not even sure what you have installed in the amp you are working on. Pics will help us help you get er done.
 
Yeah, sorry guys. Thanks for all the help you've given to this and other projects. It must be frustrating that I don't work straight through and finish this thing. Unfortunately, that hasn't been possible for me. Truth is, I'm fully disabled, and when, what, and for how long I can work on things is completely out my hands. That said, these projects have been a literal life saver. So, thank all of you very much. I genuinely appreciate your expertise and generosity.
I'll send pictures, but it's completely White Oak parts. The problem is that one channel is just dead. It isn't blown, it just isn't producing sound or voltage at the bias check point. I'm getting + and - 15 volts on the regulators, and all the fuses and resistors check out as good. However, I'm not sure what other voltages or continuity I can check in circuit that would be of any value or help. The speaker protect relay is new and could possibly be a problem, but it seems to be working, and it comes after the bias anyway. So I don't think it's in the loop that's giving me problems. I'm having a string of good days now, so I'm eager and able to work on this thing, for a while at least. I thought I had it, until the channel showed up dead. All the repairs to the other channel worked out great. Thanks again, very much!
I have a lot of other pictures, but I've checked every connection and wire placement. Still, it has to be either an incorrect connection or a failed component of some sort. I'm just not certain as to how to continue with the diagnosis.

WOPL — F3.jpg
WOPL — F1.jpg
 
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