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My New Early Model PL400 w/ 4 Fin Heat Sink
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- Jan 14, 2011
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- Halfbiass...Electron Herder and Backass Woof
- Joined
- Jan 14, 2011
- Messages
- 74,829
- Location
- Gillette, Wyo.
- Tagline
- Halfbiass...Electron Herder and Backass Woof
- Joined
- Jan 14, 2011
- Messages
- 74,829
- Location
- Gillette, Wyo.
- Tagline
- Halfbiass...Electron Herder and Backass Woof
When you say base drives do you mean disconnect 3L&R and 9L&R?
Can I assume that the WOA board is causing the problem somehow? I think I'm going to have to go through the build with a fine tooth comb. One thing that did happen when I was soldering it, I installed Q3, 4,5L backwards. I noticed it right away but obviously had to desolder and resolder those 3 MPSA42's. I don't think I soldered all 3 legs before noticing. I think only one leg had to be heated to pull it off.
Can I assume that the WOA board is causing the problem somehow? I think I'm going to have to go through the build with a fine tooth comb. One thing that did happen when I was soldering it, I installed Q3, 4,5L backwards. I noticed it right away but obviously had to desolder and resolder those 3 MPSA42's. I don't think I soldered all 3 legs before noticing. I think only one leg had to be heated to pull it off.
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A couple of questions / concerns about possible cause of this overcurrent situation.
*would loosing connections with one of the back wall thermal transistors be a source? When fiddling with the heatsinks there was a lot of stress put on those connections. At least once I lost my hold on the WOA board and that connection got a yank. What is the recommended replacement if this is the case?
*I have a concern about Q3, 4,5L and also the right side. The left side probably got a little over heated when I put them in backwards (never powered this way). Both the left and right have got flexed several times with the heatsinks sticking up so high. Could their little chain of three cause this if one were bad or have a crack in a lead?
*I kept asking about disconnecting power to the WOA board just to see if removing it from the equation would allow proper DBT operation.
*none of the TO220 transistors, that have heatsinks, have any sort of insulation from the pcb. Just want to make sure this is correct.
*I'm going to go through the BOM an make sure that there are no errors in parts placement.
*would loosing connections with one of the back wall thermal transistors be a source? When fiddling with the heatsinks there was a lot of stress put on those connections. At least once I lost my hold on the WOA board and that connection got a yank. What is the recommended replacement if this is the case?
*I have a concern about Q3, 4,5L and also the right side. The left side probably got a little over heated when I put them in backwards (never powered this way). Both the left and right have got flexed several times with the heatsinks sticking up so high. Could their little chain of three cause this if one were bad or have a crack in a lead?
*I kept asking about disconnecting power to the WOA board just to see if removing it from the equation would allow proper DBT operation.
*none of the TO220 transistors, that have heatsinks, have any sort of insulation from the pcb. Just want to make sure this is correct.
*I'm going to go through the BOM an make sure that there are no errors in parts placement.
Went through BOM item by item and found no parts mis-placement. I thought I found something but it turns out it was nothing.
R53 Actual=Brown Grey Violet Brown Brown (1.87K Ohm Correct per description) vs BOM said Brown Grey Black Brown (1.8K Ohm)
R35L R35R R37L R37R Actual = Red Red Black Gold Brown (22 Ohm) vs BOM 22.1 Ohm (I'm guessing .1 Ohms does not make a difference)
R36L R36R Actual=Green Blue Black Gold Brown (56 Ohm Correct per description) vs BOM Green Blue Black Black (560 Ohm)
I couldn't check the MPSA92 and MPSA42 because I'm afraid to remove the heatsinks.
R53 Actual=Brown Grey Violet Brown Brown (1.87K Ohm Correct per description) vs BOM said Brown Grey Black Brown (1.8K Ohm)
R35L R35R R37L R37R Actual = Red Red Black Gold Brown (22 Ohm) vs BOM 22.1 Ohm (I'm guessing .1 Ohms does not make a difference)
R36L R36R Actual=Green Blue Black Gold Brown (56 Ohm Correct per description) vs BOM Green Blue Black Black (560 Ohm)
I couldn't check the MPSA92 and MPSA42 because I'm afraid to remove the heatsinks.
I thought I'd check the bias resistors since I thought the connection might be compromised. I only have a cheapie Chinese testor but it does tell me which lead is what. Good news is the Bias Xistors are still have a good connection. Bad news is based on the testor my colors do not match the narrative connection table.
Table for Bias Xistor-------Per Cheap Testor
C = Red--------------------Red
B = Black-------------------Brown
E = Brown------------------Black
Could this mis-wiring of the Emitter and Base cause the problems I'm seeing?
Table for Bias Xistor-------Per Cheap Testor
C = Red--------------------Red
B = Black-------------------Brown
E = Brown------------------Black
Could this mis-wiring of the Emitter and Base cause the problems I'm seeing?
Alan
A trick if you think you are suspecting bias transistor problems is to put a short jumper wire between the C and E connection points on the control board. Since you have the Phoenix connectors, this is easy for you to do. It eliminates the bias but you do not care about that at this moment, you just want to complete a successful bring up. If it comes up successfully after that then you have narrowed the problem down to the bias transistors which you can then troubleshoot.
Joe
A trick if you think you are suspecting bias transistor problems is to put a short jumper wire between the C and E connection points on the control board. Since you have the Phoenix connectors, this is easy for you to do. It eliminates the bias but you do not care about that at this moment, you just want to complete a successful bring up. If it comes up successfully after that then you have narrowed the problem down to the bias transistors which you can then troubleshoot.
Joe
Cheap Chinese Tester to the rescue! Rewired the bias transistor per the results of the CCT and the 400 powered up properly. As soon as I started to increase the variac, the B+ increased as well! The relay kicked in at about 110VAC. Once at 120VAC the offset was -.4mV on left and -.2mV on the right.
Glad you are operational Alan. The photos of your bias transistors seem to have heat shrink encapsulating the body of the transistor. Is that the case or is it just the photo?
The transistor body should be in direct contact with the metal P strap to provide the best thermal conduction path possible since this transistor is responsible for servo'ing the bias current based on temperature sensed at the back wall of the amp.
There should be no insulation between the TO-220 transistors and the heatsinks.
The transistor body should be in direct contact with the metal P strap to provide the best thermal conduction path possible since this transistor is responsible for servo'ing the bias current based on temperature sensed at the back wall of the amp.
There should be no insulation between the TO-220 transistors and the heatsinks.