So this has been a particularly rough week; on Sunday evening I attempted to replace the diode bridge and managed to put reversed polarity to my amp. I feel like I stepped in front of a bus.
So now I am sorting out the damage, all while questioning my judgement to have allowed this to happen.
A 100uf bypass that was before the board had blown, as it heated up the quickest.
Using the suggested power test points from the dh200 manual, it looks like the transistors are giving the incorrect readings now, but the diodes are all ok it appears.
I have 26vdc on the output of one channel, and 1 volt on the other, amp plays.
What step would be next to keep from destroying any more components?
Can I work on the driver boards without the outputs connected to keep from taking those out or is the load necessary for getting proper readings I am wondering?
So now I am sorting out the damage, all while questioning my judgement to have allowed this to happen.
A 100uf bypass that was before the board had blown, as it heated up the quickest.
Using the suggested power test points from the dh200 manual, it looks like the transistors are giving the incorrect readings now, but the diodes are all ok it appears.
I have 26vdc on the output of one channel, and 1 volt on the other, amp plays.
What step would be next to keep from destroying any more components?
Can I work on the driver boards without the outputs connected to keep from taking those out or is the load necessary for getting proper readings I am wondering?
Sorry to read about your experience. I am about to replace the 2 20,000uF caps and the bridge rectifier with a HiperFRED diode. But I've never done this before.
Can I just swap out the parts or do I also have to change other resistors, therms, etc? I don't even know if I need to keep the snubber across the bridge rectifier and power switch.
Can I just swap out the parts or do I also have to change other resistors, therms, etc? I don't even know if I need to keep the snubber across the bridge rectifier and power switch.
Hello,
Whats going to blow in the circuit path"what components" if you swap the outputs +/- out of the bridge rectifier? Stupid mistake was distracted by wife 🙁 The boards are a pc 10 🙁 too!!! I need a quick response please...
Whats going to blow in the circuit path"what components" if you swap the outputs +/- out of the bridge rectifier? Stupid mistake was distracted by wife 🙁 The boards are a pc 10 🙁 too!!! I need a quick response please...
FYI, Musical Concepts / Musical Design has been modifying and repairing Hafler gear for over 30 years. They have their own circuit boards and power supply upgrades. Musical Concepts / Musical Design Home
Hafler DH-500 problems
I have a DH-500 purchased new that originally had PC-19 boards. I also have several DH-200 amps as well as a P230. Most of them I've upgraded with a new JFET cascode driver board kit by Quaco. Go to EBAY and search hafler and you'll see a lot of parts for Haflers available from QUACO. It is stuff sold by an engineer who used to work for Hafler and Dynaco. He has kits for the caps on the driver boards, semi-conductors for the driver boards, switches, large PS caps, and a lot of other stuff.
The JFET cascode driver board kit that he sells turns your amp into something close to or better than an XL-280 or XL-600. The imaging on mine is quite good after the upgrade. He also sells the Power MOSFETS for the outputs. In summary, you have a lot of options for repair as well as upgrade. FYI, I believe the PC-10 boards didn't have the pot for adjusting DC offset. IF that is off then you may need to replace the input transistors with a matched set.
BTW, a properly working DH-500 can drive a pretty difficult load. I once had a short on one speaker wire and the amp just kept working but with greatly reduced output. My only initial clues were the low volume on one channel and the fan switching to high speed
I have a DH-500 purchased new that originally had PC-19 boards. I also have several DH-200 amps as well as a P230. Most of them I've upgraded with a new JFET cascode driver board kit by Quaco. Go to EBAY and search hafler and you'll see a lot of parts for Haflers available from QUACO. It is stuff sold by an engineer who used to work for Hafler and Dynaco. He has kits for the caps on the driver boards, semi-conductors for the driver boards, switches, large PS caps, and a lot of other stuff.
The JFET cascode driver board kit that he sells turns your amp into something close to or better than an XL-280 or XL-600. The imaging on mine is quite good after the upgrade. He also sells the Power MOSFETS for the outputs. In summary, you have a lot of options for repair as well as upgrade. FYI, I believe the PC-10 boards didn't have the pot for adjusting DC offset. IF that is off then you may need to replace the input transistors with a matched set.
BTW, a properly working DH-500 can drive a pretty difficult load. I once had a short on one speaker wire and the amp just kept working but with greatly reduced output. My only initial clues were the low volume on one channel and the fan switching to high speed
Speaking from experience;
1) Output transistors (2 matched sets of 3+3).
2) Numerous smaller transistors and possibly diodes, and electrolytic capacitors on the 2 PC-10 driver boards.
3) The 2 large power supply capacitors, possibly, depending on how much time they had been exposed to reverse polarity.
4) Your confidence in working on future projects for an undetermined amount of time, which may be deserved in cases like this. I consider myself very lucky to have not had a large capacitor embedded in my body somewhere. I’ve seen batteries blow up and enter a leg before, it happens.
Thanks for the alternative driver board options, will likely be the path I will be taking since the original boards aren’t as reliable I have found after 4 sets now.
Hafler DH-500 problems
Phase is correct. There are probably a bunch of components that may have failed. Even if the PS caps are good I recommend changing them out due to age later on when your budget permits. The result in my experience was better low frequency performance. For all the old Hafler amps I've acquired I have installed capacitor upgrade kits (from QUA-CO), then later on the PS caps, then ultimately the new driver boards. This seems to me to be the most reasonable upgrade order.
IF you decide to repair the existing driver boards then I'd still recommend replacing the caps but in addition get the semi-conductor repair kit and replace all the transistors instead of risking more damage trying to trouble-shoot what may be failed. The only thing left would then be resistors which can be checked before installing the semi-conductors. The way I look at it, I have amps that should last another 30-40 years and I've saved a ton of money compared to buying something new of similar performance.
Phase is correct. There are probably a bunch of components that may have failed. Even if the PS caps are good I recommend changing them out due to age later on when your budget permits. The result in my experience was better low frequency performance. For all the old Hafler amps I've acquired I have installed capacitor upgrade kits (from QUA-CO), then later on the PS caps, then ultimately the new driver boards. This seems to me to be the most reasonable upgrade order.
IF you decide to repair the existing driver boards then I'd still recommend replacing the caps but in addition get the semi-conductor repair kit and replace all the transistors instead of risking more damage trying to trouble-shoot what may be failed. The only thing left would then be resistors which can be checked before installing the semi-conductors. The way I look at it, I have amps that should last another 30-40 years and I've saved a ton of money compared to buying something new of similar performance.
I have gotten tired of poking around on boards that are nearly 40 years old with corroding leads/cold joints everywhere. After some four sets of second hand boards, the amp is now resting in a safe place away from any power source until I can scrape together the funds for some newer driver boards. I didn’t have a problem with the sound of a pooged original, however they were not reliable long term imo.
I think you can still get the bare PC-19 boards, and build them up using components or kits even. I am just not sure it would be worth my time when better options exist.
The output mosfets are available from here(see below) once you’ve determined that some are smoked from each channel. You will have to ask the seller to match them in sets of three pairs for each channel on the DH500, since these amps do not have source resistors to handle differences between them.
2SK134 2SK135 2SK176 2SJ49 2SJ50 2SJ56 ECF10N20 ECF10P20 EXICON SET | eBay
I think you can still get the bare PC-19 boards, and build them up using components or kits even. I am just not sure it would be worth my time when better options exist.
The output mosfets are available from here(see below) once you’ve determined that some are smoked from each channel. You will have to ask the seller to match them in sets of three pairs for each channel on the DH500, since these amps do not have source resistors to handle differences between them.
2SK134 2SK135 2SK176 2SJ49 2SJ50 2SJ56 ECF10N20 ECF10P20 EXICON SET | eBay
Hafler DH-500 problems
I agree
If it were mine I would buy all new MOSFETs from Qua-co to get matched sets. If any of the old ones are still good then you can sell them. That's what I did on one amp. I would also get the new driver boards from the same source. Install an in-rush current limiter and eventually new PS caps and you have an amp that will last for many years.
I agree
If it were mine I would buy all new MOSFETs from Qua-co to get matched sets. If any of the old ones are still good then you can sell them. That's what I did on one amp. I would also get the new driver boards from the same source. Install an in-rush current limiter and eventually new PS caps and you have an amp that will last for many years.
- Status
- Not open for further replies.