@jan.didden: I'm confident the cable is fine, I didn't touch it. It's the connector pins I'm worried about. I'm going to redo the pins and get that all cleaned up, then I'll test everything. I'll also redo the mod as @JMFahey suggests. For the purposes of this mod, does it make a difference if the capacitors connect to ground or common? The guide said ground, so that's what I'm going with.
@rayma. Will test, thank you.
@rayma. Will test, thank you.
In that case it is even simpler. Check the voltages that 'come out of the cable' at the point where the connector pins connect to the board (I assume there are wire links?) versus the schematic diagram. The mod talks about pulling back cable insulation so you can solder the caps to the wire - is that the wire link from connector to PCB or what?
But let's focus. I agree with @rayma that if three regulators all output 0V, it's very likely not the regulators but the input voltage to the regulators that is at fault. Where does that (22VDC?) come from? Your circuit shows a power xformer and a rectifier that provides 22VDC feeding the regulators, which as I understand it, is all before the umbilical. So why are we worrying about the cable, if the power transformer/rectifier may be at fault?
Thinking it through.
Jan
But let's focus. I agree with @rayma that if three regulators all output 0V, it's very likely not the regulators but the input voltage to the regulators that is at fault. Where does that (22VDC?) come from? Your circuit shows a power xformer and a rectifier that provides 22VDC feeding the regulators, which as I understand it, is all before the umbilical. So why are we worrying about the cable, if the power transformer/rectifier may be at fault?
Thinking it through.
Jan
The mod wants the capacitors to be connect where the wires come out of the connector in the preamp. Basically soldering to the back of the pin, almost. I've been measuring voltages where the wires connect with the PCB, at the input for each pair of tubes.
I measured the input voltage to common and got 23.33VDC for block "A" (problem block) and 25.88 VDC for block "B".
I rechecked the three regulators in block A. The first two produce ~0V at their output (before the resistor). The third produces 4.5VDC
My suspicion at this point is that I shorted something at some point and totally fried two regulators, and partially fried the third. If thats true, I should be able to replace the regulators, replace pins/clean up wires going into the plug on the preamp side, and complete the mod by connecting the capacitors from the point the wire meets the PCB.
I measured the input voltage to common and got 23.33VDC for block "A" (problem block) and 25.88 VDC for block "B".
I rechecked the three regulators in block A. The first two produce ~0V at their output (before the resistor). The third produces 4.5VDC
My suspicion at this point is that I shorted something at some point and totally fried two regulators, and partially fried the third. If thats true, I should be able to replace the regulators, replace pins/clean up wires going into the plug on the preamp side, and complete the mod by connecting the capacitors from the point the wire meets the PCB.
Those regulators have internal fold-back current limiting protection and thermal shutdown, and should not fail if shorted.
If there are shorts to ground at their outputs, that would cause the protection to pull down the output voltages.
If there are shorts to ground at their outputs, that would cause the protection to pull down the output voltages.
That is true, but Reality is a harsh mistress, lots of times I have replaced blown regulators.
Not only me but tons of other Techs did.
So not surprised at all for these (possibly) having problems.
Not only me but tons of other Techs did.
So not surprised at all for these (possibly) having problems.
I can pull them to test. What's the best method? I've been comparing them to the working block in-circuit. Resistance between input and ground is OL on the good ones, but a rising value starting around ~150 ohms on the bad ones.
There's a large capacitor at their inputs. The DVM should charge when reading resistance.
You can tell if the regulator is bad or if the umbilical connector is shorted by pull out one leg of all three 7.5Ω resistors on the board and measuring the regulator's output voltage.
Alternatively, if that's easier, you can desolder the wires connected to the umbilical connector.
Alternatively, if that's easier, you can desolder the wires connected to the umbilical connector.
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What you have posted so far implies a short on the regulator outputs.
But at this point, I would remove one regulator and test it on a breadboard for proper operation.
If it fails testing, replace all three.
ARC PWBs are extremely fragile, and require skilled work to avoid damage.
But at this point, I would remove one regulator and test it on a breadboard for proper operation.
If it fails testing, replace all three.
ARC PWBs are extremely fragile, and require skilled work to avoid damage.
Look at the circuit. One set of regulators returns to 122V and the other floats. First be careful around that stuff, its dangerious. Second check between the supply and its specific return. Not the chassis. The filaments are biased to lower noise etc. . . Also the 12V has a dropping resistor to drop the 15V which could fail. It would run hot- probably around 1-2 Watts. Lots more when the tubes are warming up.
Makes sense.
I think at some point (can't find it back) you mentioned the connection of the resistors/capacitors 'between the wires and screens and ground' or something similar. Is there chance that at some point the screen of a wire is connected to the wire itself? That would short it out.
Jan
@jan.didden: If I said that, I misspoke. I only connected the capacitors from the wires to chassis ground.
@rayma
Can you elaborate on this? The appear to be quite overbuilt, but I don't have enough experience to judge. In what ways must one be careful working with their boards?
Update:
I removed one of the "bad" regulators. I connected it to the 24v input rail on the power supply, and to ground, then measured the voltage output to ground and to common. Still zero (<100mv). I then tried the diode test from my meter on it and got 0v across the pins. I tried the same test on one of the "good" regulators and got 0.625v.
Is there anything else I should try, or can I declare them dead?
@rayma
Can you elaborate on this? The appear to be quite overbuilt, but I don't have enough experience to judge. In what ways must one be careful working with their boards?
Update:
I removed one of the "bad" regulators. I connected it to the 24v input rail on the power supply, and to ground, then measured the voltage output to ground and to common. Still zero (<100mv). I then tried the diode test from my meter on it and got 0v across the pins. I tried the same test on one of the "good" regulators and got 0.625v.
Is there anything else I should try, or can I declare them dead?
Seems to be bad.
But the important thing is to determine why.
They don't fail for no reason.
These are the elevated regulators? Maybe that has something to do with it.
But the important thing is to determine why.
They don't fail for no reason.
These are the elevated regulators? Maybe that has something to do with it.
Based on what I know about what I did, it seems very likely that I shorted something, without realizing it, potentially for an extended period of time. "Technician error" seems most plausible.
I have sourced replacements from Audio Research. I will thoroughly test both power supply and preamp before I reconnect them.
I have sourced replacements from Audio Research. I will thoroughly test both power supply and preamp before I reconnect them.