Many things to check.
Does the pilot light come on(power switch)?
(no light, no power on primary side: switch, cord, fuse, fuse holder, transformer))
Is it steady or does it blink?
(blink? bad thermostat)
Are the internal fuses OK? ±93V at both channels?
(15A line fuse, bad rectifier)
How much DC is on the output of either channel?
(trip point is less than 2V)
Could be 48V relay coil, could be drive transistor, could be the C in the RC time delay.
Check all in the order suggested.
Does the pilot light come on(power switch)?
(no light, no power on primary side: switch, cord, fuse, fuse holder, transformer))
Is it steady or does it blink?
(blink? bad thermostat)
Are the internal fuses OK? ±93V at both channels?
(15A line fuse, bad rectifier)
How much DC is on the output of either channel?
(trip point is less than 2V)
Could be 48V relay coil, could be drive transistor, could be the C in the RC time delay.
Check all in the order suggested.
Sorry I thought you could see the light on solid from there ;-}
5 Internal fuses check fine, 2 external as well, + _ 93Volts fine on both sides
How much DC is on the output of either channel?
(trip point is less than 2V)
??
0V unless I measured this wrong. Just on low scale DC between - and + output posts? If so 0V.
Assuming 0V is correct, how do I check the relay coil or is it just replace the parts you mentioned untill it works? I understand some electronics but never learned to troubleshoot to component level. I can replace the parts easy enough once located though. I truly appreciate your help. I miss my music and the boom box with 3" speakers with bass boost is making me cranky. At least that's my excuse.
5 Internal fuses check fine, 2 external as well, + _ 93Volts fine on both sides
How much DC is on the output of either channel?
(trip point is less than 2V)
??
0V unless I measured this wrong. Just on low scale DC between - and + output posts? If so 0V.
Assuming 0V is correct, how do I check the relay coil or is it just replace the parts you mentioned untill it works? I understand some electronics but never learned to troubleshoot to component level. I can replace the parts easy enough once located though. I truly appreciate your help. I miss my music and the boom box with 3" speakers with bass boost is making me cranky. At least that's my excuse.
Take it to a good tech, please
I don't mean to be offensive, but from the description of your electronic abilities you may not have the background to safely work on this amp, or have much chance of repairing it. I know that sounds pretty snooty, but this is a big amp with hihg voltages and repair parts are expensive and hard to find if you do torch it. I have the schematics and manuals for this amp, and know it pretty well, having repaired a number of them, so I know what I am saying here.
The real risk is that you will fry the output mosfets, which are very difficult to find and very expensive. There are 12, and they cost $15-20 each if you can find them, but those will probably not be matched and this circuit was designed for matched triples of output mosfets. So I'd suggest hands off unless you are willing to accept the fairly high risk that you will blow the outputs.
Having said that, it could be a very simple problem of adjusting the DC balance, for which there is a pot. Observe the output voltage on both channels. If one is more than a few millivolts from zero, possibly that channel just needs a tweek. Go gently, if you don't see improvement stop and turn off the amp and leave it for an experienced repair person.
I don't mean to be offensive, but from the description of your electronic abilities you may not have the background to safely work on this amp, or have much chance of repairing it. I know that sounds pretty snooty, but this is a big amp with hihg voltages and repair parts are expensive and hard to find if you do torch it. I have the schematics and manuals for this amp, and know it pretty well, having repaired a number of them, so I know what I am saying here.
The real risk is that you will fry the output mosfets, which are very difficult to find and very expensive. There are 12, and they cost $15-20 each if you can find them, but those will probably not be matched and this circuit was designed for matched triples of output mosfets. So I'd suggest hands off unless you are willing to accept the fairly high risk that you will blow the outputs.
Having said that, it could be a very simple problem of adjusting the DC balance, for which there is a pot. Observe the output voltage on both channels. If one is more than a few millivolts from zero, possibly that channel just needs a tweek. Go gently, if you don't see improvement stop and turn off the amp and leave it for an experienced repair person.
My previous post was wrong. There is no DC offset adjust on this amp. The pot I mentioned adjusts bias current and is not relevant to this problem.
In my opinion, it's still not a good idea to tackle troubleshooting this amp without the schematic, some tools and basic knowledge of electronics. Without more information than you have given, it is hard to guess where the problem lies.
In my opinion, it's still not a good idea to tackle troubleshooting this amp without the schematic, some tools and basic knowledge of electronics. Without more information than you have given, it is hard to guess where the problem lies.
slowhands said:
My DH-500 has two pots per channel - P1 is the offset adjustment, P2 is the bias adjustment. They are really cheap open pots. Cleaning them may help, better yet replace them.
Check the DC offset of the signal at the output FETS where 6 leads come together (there are no source resistors). If it is more than a few volts, something is seriously wrong, otherwise you might be able to tweak the offset back into limits.
BTW, idle bias should be 450 mA/channel. Put your ammeter in place of one of the rail fuses. I cannot hear any difference in the sound quality until I drop below 150 mA. Although I didn't listen full range for long. I use the amp to power my subwoofer.
Edit: I can scan the schematic if you need it.
There may be several versions of the PC-10 driver board for this amp, because my example and documentation only show one pot. My schematic and parts list, for SN 7117876 dated 1981, and and the physical amp have only one pot, P1, for setting bias current.
I did check the Hafler P-505 schematic, and the PC19c driver boards do have two pots, an input offset adjustment and bias set pot. Possibly the PC19C is a later version, it looks to be interchangeable with the PC10 connections. this amp is essentially identical in ratings, but has balanced XLR inputs ("Professional", no less).
I'm not sure this is much help to the fellow with the dead DH-500, but it kind of explains why I recalled the input offset pot on this series amp. It's there on some of the series, but not all.
I did check the Hafler P-505 schematic, and the PC19c driver boards do have two pots, an input offset adjustment and bias set pot. Possibly the PC19C is a later version, it looks to be interchangeable with the PC10 connections. this amp is essentially identical in ratings, but has balanced XLR inputs ("Professional", no less).
I'm not sure this is much help to the fellow with the dead DH-500, but it kind of explains why I recalled the input offset pot on this series amp. It's there on some of the series, but not all.
I'm going to make a thread all about Hafler's DH amps. The DH-500 used a PC-10 card. It was nearly the same as the DH-200's PC-6 card. The DH-220, P225, P230, later DH-500s, and others used a PC-19 card. The PC-19 went through three revisions, A, B, and the last was C. Not sure what the differences are, but the PC-19C has two pots. One for DC Offset, and one for the bias. PC-10 and PC-6 have ONE pot.. bias only.
Yeah I know this thread is dead, but thats my $0.02
Yeah I know this thread is dead, but thats my $0.02
Hello, I changed the capacitors on the PC10 board DH500 and when I attached the board to the heat sink with the little insulating washers the amp worked but I was wiggling the wires near +90 volts pin 3&4 touched the aluminum and I heard a big pop and flash of the fuse and the channel was dead so I changed the fuse and no sound. I looked all over and cant find a blown anything. What could have happened??? Please help!!!
I have worked on many of these. It's not for newbies, and not for guessing without a schematic. Which is in the manual, here:
http://www.hafler.com/pdf/archive/DH-500_amp_man.pdf
I will pray for your amp (and you!) -- there is 93 volts on power. AC line is all over the chassis. Never get approved today.
http://www.hafler.com/pdf/archive/DH-500_amp_man.pdf
I will pray for your amp (and you!) -- there is 93 volts on power. AC line is all over the chassis. Never get approved today.
Hello,
I do understand the High DC and AC voltages so what could have happened when I wiggled the wire and pushed on the board near 3&4 and hit the heat sink? I do not see any components burnt or blown up so what could have happened that the right channel does not work.Please give me some options...
I do understand the High DC and AC voltages so what could have happened when I wiggled the wire and pushed on the board near 3&4 and hit the heat sink? I do not see any components burnt or blown up so what could have happened that the right channel does not work.Please give me some options...
With power off, check all the transistors for shorts and opens. You probably shorted one of the metal can transistors, the shiny ones 2n5416 and 2n3440. Here's how to start. You must have a meter with a diode setting. At this crude testing level you want to see a diode drop of around 0.6v between the base and emitter and between base and collector, and very high resistance in the reverse polarity. For PNP and NPN the diode polarities will be reversed. Some readings will be wrong because of other components in the circuit, but check each transistor.
This might help you find the dead one. It may be shorted, or it may be open, either is bad. If you are lucky, you only blew one and not others. Change every suspect device. Test each one removed out of circuit to verify it was bad. This helps confirm you found the trouble and maybe fixed it.
But go slowly and carefully and you should zero in on it. I like to power up on a variac with a resistor load. I have a current meter on my variac that is helpful when there are still shorts. Again, this is not an amp to approach casually, because you can do lots of damage with a slipped probe, and you can get a sting from the high voltages. You must have the schematic, a good DVM with diode setting, and proceed cautiously. Don't feel bad, we have all done this and it is such a pain to track down.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.