I tried over at AK but didn’t get any hits; maybe you guys can help me?
Not really familiar Hafler equipment and this one has me stumped. I've looked at several other threads about this same topic, but I'm not having much luck. This DH-500 came to me this way - powers on, switch light is solid, but does not come out of protection. I've replaced capacitors and transistors on both channels of power amp, and replaced caps, tranisistors, and diodes on protection board (PC-9A). Also replaced Protection Relay with NOS relay.
Transistors Used:
2N5550 --> ZTX694B
2N5401 --> ZTX795A
Diodes were straight ahead replacements (1N5240B, 1N4003, and 1N4148). Caps were also value for value.
I measured DC at one side of the relay and got ~20mV; I jumped the relay and have good output for prolonged listening without excessive heating, but I'd rather keep the relay in circuit.
Do you folks have any advice?
Thanks,
Dan
Not really familiar Hafler equipment and this one has me stumped. I've looked at several other threads about this same topic, but I'm not having much luck. This DH-500 came to me this way - powers on, switch light is solid, but does not come out of protection. I've replaced capacitors and transistors on both channels of power amp, and replaced caps, tranisistors, and diodes on protection board (PC-9A). Also replaced Protection Relay with NOS relay.
Transistors Used:
2N5550 --> ZTX694B
2N5401 --> ZTX795A
Diodes were straight ahead replacements (1N5240B, 1N4003, and 1N4148). Caps were also value for value.
I measured DC at one side of the relay and got ~20mV; I jumped the relay and have good output for prolonged listening without excessive heating, but I'd rather keep the relay in circuit.
Do you folks have any advice?
Thanks,
Dan
Check the IC in the protection circuit. The amp is obviously working, so the problem lies in the relay circuit.
I should have stated I replaced the IC, as well. I forgot I’d done it as this project has sat for a while. I’ve got a bag of the IC’s, maybe I should try a few different in place? I’ll have to go back and see where they were sourced from, as they may be fakes or something...
What are the voltages on pins 3, 12, and 13 of IC101? 3 and 12 are the power supply inputs, should be +/- 10VDC. Pin 13 is the output of the comparator. Under normal conditions it will be a +DCV, in protect mode it will a -VDC. Also what are voltages on 1,2, and 3 of the board itself?
Craig
Craig
I don't know if this will look like progress or not, but here's what I got:
IC101:
Pin 3 --> -0.71 VDC (clearly an issue)
Pin 12 --> -9.62 VDC
Pin 13 --> -9.59 VDC
Board:
Pin 1 --> 0 VDC (normal?)
Pin 2 --> 86.6 VDC
Pin 3 --> 86.6 VDC
IC101:
Pin 3 --> -0.71 VDC (clearly an issue)
Pin 12 --> -9.62 VDC
Pin 13 --> -9.59 VDC
Board:
Pin 1 --> 0 VDC (normal?)
Pin 2 --> 86.6 VDC
Pin 3 --> 86.6 VDC
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When I got mine, the relay was chattering, an adjustment of the pull-down resistor on the relay board has it working as intended.
20mv should be fine.
20mv should be fine.
You are missing the +VDC to the comparator, check Zeners D101 and D108 for shorts or installed incorrectly, anode towards ground. And check both sides of R105, should have approx. +90VDC on one side and +10VDC on the other. If you are positive that there is NO DCV on the amplifier outputs pulling the IC should energize the relay. Right now with no +VDC to the comparator the base of Q101 is negative and therefore Q101 is off and the relay is not grounded. Pulling the IC will simulate the IC's normal condition, pin 13 not pulled low.
Craig
Craig
Craig,
At R105 and R110, I have +/- 87.7VDC on one side, but basically nothing on the other side of the resistors. I do have a PC-9A board, whereas the service manual I have only has the 9C board shown. Pictures attached.
Do I understand you correctly that if I pull the IC, the relay should operate correctly?
At R105 and R110, I have +/- 87.7VDC on one side, but basically nothing on the other side of the resistors. I do have a PC-9A board, whereas the service manual I have only has the 9C board shown. Pictures attached.
Do I understand you correctly that if I pull the IC, the relay should operate correctly?
An externally hosted image should be here but it was not working when we last tested it.
Apologies for jumping in but have you fixed this yet ?
Your readings seem inconsistent... you say you have approx. -10v on pin 12 (which is correct) and then you go on to say there is nothing on one side of R110 (which is the pin 12 end).
The voltage across each pair of zeners should be around 10 volts giving PLUS 10 on pin 3 and MINUS 10 on pin 12.
Both resistors (R105 and R110) should be equally 'hot' which can be a quick way of determining if one is open circuit, although only check this after switching off as 90 volts DC is classed as a dangerous voltage.
If the plus 10 volts is missing then it can really only be the resistor feed open circuit, one of the zeners short, or the IC faulty. The resistor is favourite.
Your readings seem inconsistent... you say you have approx. -10v on pin 12 (which is correct) and then you go on to say there is nothing on one side of R110 (which is the pin 12 end).
The voltage across each pair of zeners should be around 10 volts giving PLUS 10 on pin 3 and MINUS 10 on pin 12.
Both resistors (R105 and R110) should be equally 'hot' which can be a quick way of determining if one is open circuit, although only check this after switching off as 90 volts DC is classed as a dangerous voltage.
If the plus 10 volts is missing then it can really only be the resistor feed open circuit, one of the zeners short, or the IC faulty. The resistor is favourite.
I flipped the zener on the right side of the board that feeds pin 3 to match the side that feeds pin 12; I have voltage now at pin 3 (-8.5VDC). I'm going to pull R105 and test, as I have +87.7VDC on one side...and -8.5VDC on the other. Is that even possible?
EDIT: I put the zener back the way it was in the picture. That was not the issue.
EDIT: I put the zener back the way it was in the picture. That was not the issue.
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D101 and D108 should have the stripe end connecting to pin 3 of the chip.
D102 and D107 should have the stripe end connecting to ground.
D102 and D107 should have the stripe end connecting to ground.
It was the resistor! Voltages are correct now and the relay kicks as it should. Thanks so much, guys!
Finally, is there anything else recommended for adjustment before I start using this amp?
Finally, is there anything else recommended for adjustment before I start using this amp?
I used to dream of faults like that 🙂
A check of bias current would be advisable if the amp has an unknown history but be careful and don't short anything out. And check for dries.
Its always hard to second guess potential issues, all we can say is the fault as presented is a 'definite' and there are no contributing factors over its failure.
A check of bias current would be advisable if the amp has an unknown history but be careful and don't short anything out. And check for dries.
Its always hard to second guess potential issues, all we can say is the fault as presented is a 'definite' and there are no contributing factors over its failure.
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