First of all a big thanks to everyone who contributes here...I wouldn't have completed the project without it. Now a disclaimer. I have restored a couple of tube integrated amps, a Sherwood tube receiver and a very early Sherwood solid state receiver..... And up until a couple of days ago a successful full WOPL PL 400. I'm learning as I go but all I've done was only possible due to pretty specific information on what to do. As Dirty Harry said "A man's got to know his limitations". My limitations are somewhere in that big gap between being able to follow instructions/replace items and truly understanding/diagnosing a problem. That said, here's my problem.
Between the kit instructions and info on here I managed a successful full WOPL upgrade. Have to say the accomplishment felt good as it was a one time through, no problems experience. Once that was done I felt the whole deal was worthy of the light bar upgrade. So once I got it I did the install. I was ready for the test run so I hooked it to the variac and was ready. It was in the typical heat sink down/face plate up working position. I flipped the face plate back into position to better see the meters. I started to increase voltage on the variac and when I hit around 60-70v I saw some smoke....I quickly turned down the variac and said some bad words. I turned it off and lifted the face plate and said several more bad words as I saw two of the wires that connect to the meters dangling down. Some massive brain fart resulted in me somehow not connecting two wires to the meter terminals before I flipped the plate into place. Once the cussing stopped I started looking for the smoke source. I found a blackened resistor on the right channel side of the control board, lower right corner. ( I've included pictures of the charred resistor in hopes the location can help with a diagnosis ). I didn't see any other burn marks, etc.
Once the cussing stopped I replaced the resistor and attached the meter wires (bringing back bad memories and causing me to mumble insults at myself). With that hope that you can't help but have (yet you know is likely to melt away) I plugged it back into the variac and started to up the voltage. Short version...I made it to full power, no fuses blew, the speaker protection relay clicked into action, the meter lights lit up and no smoke signals. I optimistically moved on to an actual speaker test. I powered down, hooked up my test speakers and powered back up. Then I went to plug in the rca cable to the left amp output. As soon as the connector made contact, the speaker made something of a popping sound followed by a loud hum. Actually let's call it a very loud hum. After a quick disconnect I tried the right channel and the same thing happened. The rca cable was not connected to any source. The loud hum is triggered by simply connecting the cable to the amp.
I did the smart thing and left the workbench for the night. I knew my next step was to get to this forum as my diagnostic ability stopped at the black resistor. As I said, I included a couple of pictures of the affected resistor. I figured that someone may want the values from the test points on the boards so I went back to the scene of the crime. They are as follows.
Left channel back plane: Bias+ = .360v... B+ = 78v... Output = 0... Bias- = -.364v... B- = -78v
Right channel back plane: Bias+ = .365v... B+ = 78v... Output = 0... Bias- = -.365v... B- = -78v
Control board bias: Right: .364v and Left: .364v
Thanks in advance for any help and please bear with me when it comes to working on this....My free time has no schedule so please don't think a slow response means I'm not working at it. Not about to be done in by my own hand.
Between the kit instructions and info on here I managed a successful full WOPL upgrade. Have to say the accomplishment felt good as it was a one time through, no problems experience. Once that was done I felt the whole deal was worthy of the light bar upgrade. So once I got it I did the install. I was ready for the test run so I hooked it to the variac and was ready. It was in the typical heat sink down/face plate up working position. I flipped the face plate back into position to better see the meters. I started to increase voltage on the variac and when I hit around 60-70v I saw some smoke....I quickly turned down the variac and said some bad words. I turned it off and lifted the face plate and said several more bad words as I saw two of the wires that connect to the meters dangling down. Some massive brain fart resulted in me somehow not connecting two wires to the meter terminals before I flipped the plate into place. Once the cussing stopped I started looking for the smoke source. I found a blackened resistor on the right channel side of the control board, lower right corner. ( I've included pictures of the charred resistor in hopes the location can help with a diagnosis ). I didn't see any other burn marks, etc.
Once the cussing stopped I replaced the resistor and attached the meter wires (bringing back bad memories and causing me to mumble insults at myself). With that hope that you can't help but have (yet you know is likely to melt away) I plugged it back into the variac and started to up the voltage. Short version...I made it to full power, no fuses blew, the speaker protection relay clicked into action, the meter lights lit up and no smoke signals. I optimistically moved on to an actual speaker test. I powered down, hooked up my test speakers and powered back up. Then I went to plug in the rca cable to the left amp output. As soon as the connector made contact, the speaker made something of a popping sound followed by a loud hum. Actually let's call it a very loud hum. After a quick disconnect I tried the right channel and the same thing happened. The rca cable was not connected to any source. The loud hum is triggered by simply connecting the cable to the amp.
I did the smart thing and left the workbench for the night. I knew my next step was to get to this forum as my diagnostic ability stopped at the black resistor. As I said, I included a couple of pictures of the affected resistor. I figured that someone may want the values from the test points on the boards so I went back to the scene of the crime. They are as follows.
Left channel back plane: Bias+ = .360v... B+ = 78v... Output = 0... Bias- = -.364v... B- = -78v
Right channel back plane: Bias+ = .365v... B+ = 78v... Output = 0... Bias- = -.365v... B- = -78v
Control board bias: Right: .364v and Left: .364v
Thanks in advance for any help and please bear with me when it comes to working on this....My free time has no schedule so please don't think a slow response means I'm not working at it. Not about to be done in by my own hand.
