Resurrected a Customized WOPL 400
- Thread starter scottonnob
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Scott, try this. Comparison testing. You have one working channel so you can isolate the issue in the faulty channel. Each channel is a mirror image of the other, so.
Power the amp, DMM set to VDC. Black DMM lead clipped to the star ground (copper bar between caps).
Start on the backplanes in a methodical order testing voltage with the red lead. Test a point on the good channel, then the same point on the bad. Eventually you'll find a discrepancy between the channels.
Then think about what's causing it, and use diode and resistance functions on the DMM to find the fault in that area (power it down first of course).
Just be damn careful not to slip the probe causing a short and more issues. Also recognize B+ and B- are 80 VDC.
Once you find and fix the fault then the boards and wiring can be cleaned up some.
Let us know how it goes and we'll try to help.
Power the amp, DMM set to VDC. Black DMM lead clipped to the star ground (copper bar between caps).
Start on the backplanes in a methodical order testing voltage with the red lead. Test a point on the good channel, then the same point on the bad. Eventually you'll find a discrepancy between the channels.
Then think about what's causing it, and use diode and resistance functions on the DMM to find the fault in that area (power it down first of course).
Just be damn careful not to slip the probe causing a short and more issues. Also recognize B+ and B- are 80 VDC.
Once you find and fix the fault then the boards and wiring can be cleaned up some.
Let us know how it goes and we'll try to help.
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Comparing the two boards, all is well and equal for the B+ and B- voltage. Left board, the good one, shows correct voltages at base and emitter of all TO-3s, roughly .380V. Right side bases and emitters are dead. Collectors on both sides show appropriate voltages. As stated earlier, there are no blown resistors or pico fuses on either board. However, most of the resistors on the dead channel show no voltage, even though they all show continuity. The bias transistors test as not blown, but the right side is getting low to no voltage: E - .333V, B - .334V, C - .363V. Left bias transistor voltage: E - 1.43V, B - .777V, C - +1.47V. The board layout sheet I have is for Rev. B. My board is Rev. C. So I don’t have the resistor numbers in front of me, but all those at the TO3s on the right side show no voltage. All caps show same voltage on both boards. Diodes all show same voltage. Bias check pin on right backplane board still reads zero.
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Sounds a lot like the bias issue I had after I nuked Linda. R-9,10,11 on the back plane and also the 10ohm bias resistors were nuked. If I remember right 9,10,11 (or at least one of them) was a 1ohm resistor that checked ok with a DMM but wouldn’t carry any current (open under load). Maybe recheck things on the backplane...
Your getting there Scott. Do more checks and think about the cause.
Also consider the missing voltages could be due to a missing, broken, or cut B+, B-, or ground wire rather than a bad component. You daisy chained your back planes together from the right side of the left back plane to the right back plane. Are all the needed wires there?
Also consider the missing voltages could be due to a missing, broken, or cut B+, B-, or ground wire rather than a bad component. You daisy chained your back planes together from the right side of the left back plane to the right back plane. Are all the needed wires there?
Was thinking the same, would check all the jumper from the Lt side board to the Rt side and double check w Joe's documentation also the jumper have to have the clear tube over it. or missing jumpers
Visual Check #1 - all components for the correct orientation and polarity . Diodes, Cap's , bias Transistors for the correct wire color. take your time.
Component Check -Check Transistor Location and the correct one are install and document it ,,,, make sure it is correctly installed and check w left channel and also use the schematic and drawings *Double check*
Check wires - double check all wiring locations and Colors
Wiggle test - Use a small wood stick and move stuff see if and components move (could be bad solder joint or forgot to solder in)
Resistors Check - Ohm out one by one all resistors from the Lt channel to the Rt channel
Wiggle Test w power on - Same as above , will see it work than it wont, I also tap around the board
Good luck
Visual Check #1 - all components for the correct orientation and polarity . Diodes, Cap's , bias Transistors for the correct wire color. take your time.
Component Check -Check Transistor Location and the correct one are install and document it ,,,, make sure it is correctly installed and check w left channel and also use the schematic and drawings *Double check*
Check wires - double check all wiring locations and Colors
Wiggle test - Use a small wood stick and move stuff see if and components move (could be bad solder joint or forgot to solder in)
Resistors Check - Ohm out one by one all resistors from the Lt channel to the Rt channel
Wiggle Test w power on - Same as above , will see it work than it wont, I also tap around the board
Good luck
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Yeah, thanks guys. I'm going to follow the power by tracing the schematic from the jumpers, all the way till I find something. I'm at a loss to explain why it's been so difficult to find where the power stops. I've already checked every connection with a DMM while also doing the wooden stick probe-athon. I still don't have a Rev. C board layout drawing which I'd like to use in order to put down the value of each resistor. Unfortunately, the numbers are covered up. I have the layout for the driver board, but I can't even figure out where the Rev B drawing came from. It was just in the big file folder. But I'll go at one more time tonight.
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- Halfbiass...Electron Herder and Backass Woof
I have to agree with Perry here, Trouble shooting this is just gonna lead you in never ending circles. Maybe pick up some cheap solder project kit to practice your soldering first, a complete redo for the amp is definitely the best idea.....
Maybe I missed it in a previous post but what solder and soldering equipment are you using?
Maybe I missed it in a previous post but what solder and soldering equipment are you using?