Hi all,
I bought a dusty Hafler DH-220 last year and am finally getting around to working on it. When I purchased it, it had crackling sounds on the right channel, but worked.
I knew it needed the electrolytic caps replaced, and figured that a new set of transistors for Q1-Q6 was a good investment. I got them from ebay along with a power supply capacitor (and bridge rectifier) upgrade. Those seemed to go fine, so I powered up on a DBT (all went as expected) and set to biasing. Left channel went as hoped, but the right channel is totally unresponsive. It measures .009 ma and turning P2 has no effect.
I've read many of the same problem from other folks here, so i started pulling resistors and diodes to check values (and replaced all with new units). R1-7, & D11-14 were all pulled and replaced. All were fine, but oddly R5 and R6 were 560 ohm, not the 1000 ohm shown on my parts schematic. is this an update?
I have checked R22-R28 in circuit, and they look to be in spec, but have not pulled them.
I have pulled all my voltages to compare to the voltages listed in the service manual. It seems all the small signal levels are off (rail voltages and ground are expected). I made a pdf with both the transistor voltages and the voltages at all the terminals and test points.
What am I missing?
I bought a dusty Hafler DH-220 last year and am finally getting around to working on it. When I purchased it, it had crackling sounds on the right channel, but worked.
I knew it needed the electrolytic caps replaced, and figured that a new set of transistors for Q1-Q6 was a good investment. I got them from ebay along with a power supply capacitor (and bridge rectifier) upgrade. Those seemed to go fine, so I powered up on a DBT (all went as expected) and set to biasing. Left channel went as hoped, but the right channel is totally unresponsive. It measures .009 ma and turning P2 has no effect.
I've read many of the same problem from other folks here, so i started pulling resistors and diodes to check values (and replaced all with new units). R1-7, & D11-14 were all pulled and replaced. All were fine, but oddly R5 and R6 were 560 ohm, not the 1000 ohm shown on my parts schematic. is this an update?
I have checked R22-R28 in circuit, and they look to be in spec, but have not pulled them.
I have pulled all my voltages to compare to the voltages listed in the service manual. It seems all the small signal levels are off (rail voltages and ground are expected). I made a pdf with both the transistor voltages and the voltages at all the terminals and test points.
What am I missing?
You nailed it first try! I pulled Q8 and it tested as a diode. Replaced it and she biased like a champ! Thank you, sir!😀