If any of the diodes are faulty (short circuit... which is how they would fail) then that is measurable in circuit.
Always try and gather the evidence by measurement rather than just replacing in hope 🙂
A readily available IN5408 would have been fine as a swap to prove the point.
Always try and gather the evidence by measurement rather than just replacing in hope 🙂
A readily available IN5408 would have been fine as a swap to prove the point.
Well measured in circuit they were showing as 001/000/001/000 in both directions, as mentioned above in post 26, with meter in diode mode.
Seemed to suggest an issue with them, hence the purchase.
Seemed to suggest an issue with them, hence the purchase.
I agree it does suggest an issue, but it would be a little unusual for all four to have failed. It might be worth you unsoldering one and testing it out of circuit just to be certain.
The diodes will measure short in circuit as they are being shunted by the transformer secondary windings, and by the supply capacitors when discharged. You ned to test them out of circuit.
Thanks for the clarification on that.
I wonder if I am better to desolder the 3 inputs from the toroidal transformer (green and 2 blue) so I can test all components in circuit?
Well I could at least just desolder one leg of a diode, that would be easy...
I wonder if I am better to desolder the 3 inputs from the toroidal transformer (green and 2 blue) so I can test all components in circuit?
Well I could at least just desolder one leg of a diode, that would be easy...
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I don't think so jaycee. In fact I've just tried it with a DVM on a PSU feeding 6800uF caps and on the diode range you see a low (but increasing) value whichever way around the leads are connected. On low ohms you see around 200 ohms and rising, again independent of lead polarity. That shows they are not short and failing short is the typical failure mode. A leaky diode simply couldn't survive in a leaky state, the current flow would fuse it short pretty much instantly.
This is why I say that 'catastrophic shorts' are measurable in circuit and the readings we are seeing of 000 and 001 are certainly that, particularly if that is on a diode range on the meter.
This is why I say that 'catastrophic shorts' are measurable in circuit and the readings we are seeing of 000 and 001 are certainly that, particularly if that is on a diode range on the meter.
I also did wonder why you had to order diodes from France, but i see the BYW98 is now obsolete. 1N5402 diodes would've worked equally well I think. No harm done 🙂
Yes, not on RS or Mouser, but some on eBay, in France. No harm done in getting them anyway, may turn out to be the problem, who knows....
Also got a FAIRCHILD SEMICONDUCTOR LM393AN Analogue Dual Comparator for good meaure. Hope I don't need it.
Plus I have a working 290 integrated if I need any major parts.
And 4 nice DNM designed split foil guided current capacitors intended for upgrade of both power amps once no. 2 is working!!
Back to work!
Also got a FAIRCHILD SEMICONDUCTOR LM393AN Analogue Dual Comparator for good meaure. Hope I don't need it.
Plus I have a working 290 integrated if I need any major parts.
And 4 nice DNM designed split foil guided current capacitors intended for upgrade of both power amps once no. 2 is working!!
Back to work!
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Not if youre not experienced. IMO, you can only reliably test them out of circuit, and its what I always do. Shrug.
OK, so I have taken out the capacitors and they appear to be fine (ran an ohm test on them and they started low and kept going up which is what should happen).
I took out one of the diodes and it measures fine.
I have previously taken out the transistors and they appeared to be fine.
Everything looks clean and fine.
Could the toroid be knackered?
Otherwise I am stumped as to where to go next and how to test the entire board.😕
I took out one of the diodes and it measures fine.
I have previously taken out the transistors and they appeared to be fine.
Everything looks clean and fine.
Could the toroid be knackered?
Otherwise I am stumped as to where to go next and how to test the entire board.😕
You can check the primary and secondaries for a short with your DMM. Also between primary and secondaries. Have you got your bulb tester up and running?
I doubt the transformer is faulty. Its dead easy to check though by simply disconnecting the secondary's. If the fuse still blows (or the bulb tester lights) then yes, either the transformer is faulty (or there is a short somewhere on the input wiring).
Its way down the list of suspects though.
You could do with finding out why you are reading 0000 or 0001 across the diodes when you do a check in circuit. On a DVM on diode range that reading means short. We need to find a reason for that. Is it a meter problem, or is there really a short there, or is it a problem in interpreting the result.
Its way down the list of suspects though.
You could do with finding out why you are reading 0000 or 0001 across the diodes when you do a check in circuit. On a DVM on diode range that reading means short. We need to find a reason for that. Is it a meter problem, or is there really a short there, or is it a problem in interpreting the result.
What do you make of the measurements of the transistors Mooly? Those made me wonder if there is something up with the multimeter
You mean this:
At face value they seem OK. The 600 readings are the internal parasitic diode across drain and source with the meter polarity agreeing on that.
The 1 ! is an odd result for any meter I have seen. Usually you would see 1.999 or similar, or perhaps a higher reading on some meters such as 3.999. Those are simply the open circuit voltage across the probes.
When short the probes you would expect to see 0000 or 0001. A short is a short is a short after all.
At face value they seem OK. The 600 readings are the internal parasitic diode across drain and source with the meter polarity agreeing on that.
The 1 ! is an odd result for any meter I have seen. Usually you would see 1.999 or similar, or perhaps a higher reading on some meters such as 3.999. Those are simply the open circuit voltage across the probes.
When short the probes you would expect to see 0000 or 0001. A short is a short is a short after all.
Yes, those. I was thinking initially the 1 was 1ohm, but I have a meter that shows 1 for an over scale reading, so that could be it. And then because of my initial assumption I thought the 6-- was far too low.
Also Peter, you didn't confirm that you are using a Time Lag (slow blow) fuse.
Also Peter, you didn't confirm that you are using a Time Lag (slow blow) fuse.
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On the diode range the meter actually displays the voltage between the test leads and so a silicon forward biased junction will be in the 550 to 750 ish region with those numbers being millivolts.
Except jaycee told him to measure on the resistance scale, which he confirmed "2000 scale"
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