Hafler DH200, DH220 restoration questions

[z-adamson]

All I ever see when it comes to folks restoring these amps is replacement of the boards with new boards and all new components.

I have never heard of anyone replacing caps, transistors, diodes etc. on the original boards.

That said, has anyone here done a restoration using original boards?

Is there a mouser parts list out there?

 

[thorpej]

As far as I'm concerned, there is zero reason to replace the original boards, especially on the DH-220. They are VERY good in stock form.

I don't see any reason to replace transistors unless they're blown. Same goes for diodes. Resistors should be checked if a part of the circuit is misbehaving... I believe those amps use carbon film resistors, which should be fairly stable over their lifetime (if they've been subject to excessive heat, that can cause them to drift up or down in value, but otherwise are fairly reliable). The electrolytic caps could be evaluated for ESR and leakage, but that requires pulling them out of circuit, so might as well replace them while you're at it (except for the main filter caps -- those are probably still fine, and easy to test because disconnecting them is fairly non-invasive).

 

[UncleBingo]

I think there are only 3 caps on the boards (one of them is bi-polar). Why not jump in there and replace them, and make notes of the other parts in there (transistors) and see if there are any known "offenders" .

 

[z-adamson]

As far as I'm concerned, there is zero reason to replace the original boards, especially on the DH-220. They are VERY good in stock form.

I don't see any reason to replace transistors unless they're blown. Same goes for diodes. Resistors should be checked if a part of the circuit is misbehaving... I believe those amps use carbon film resistors, which should be fairly stable over their lifetime (if they've been subject to excessive heat, that can cause them to drift up or down in value, but otherwise are fairly reliable). The electrolytic caps could be evaluated for ESR and leakage, but that requires pulling them out of circuit, so might as well replace them while you're at it (except for the main filter caps -- those are probably still fine, and easy to test because disconnecting them is fairly non-invasive).

I have a DH200 that is acting up.

Bias floats around from 150-450 on one channel and I would like to get it to remain steady at 275-295.

Not sure what exactly is causing this, but I would like to at the very least be able to replace any and all suspect parts.

 

[z-adamson]

I think there are only 3 caps on the boards (one of them is bi-polar). Why not jump in there and replace them, and make notes of the other parts in there (transistors) and see if there are any known "offenders" .

Correct. 3 aluminum electrolytic caps per board.

Several transistors, most of which have no labeling on them.

 

[UncleBingo]

Here: http://www.hafler.com/pdf/archive/DH-220_amp_man.pdf

Oops I mean: http://www.hafler.com/pdf/archive/DH-200_amp_man.pdf

Scroll down to page 15 for transistor parts list

 

[UncleBingo]

Diodes are all 1N4148, 1N5240B or 1N4003.

 

[Blue Shadow]

It is all covered here: http://www.diyaudio.com/forums/solid-state/31131-hafler-dh-200-220-mods.html

Take it to whatever level you want. The Musical Concepts mods when all of them are maxed out will take the amp to a very high level able to compete with a bunch of much more expensive amps. But you can do a lot just getting the list of mods done on these amps from the DIY thread. Enjoy, check back when you get done reading that. I'm about half done doing a list I put together from that thread.

 

[willyrover]

Replacement boards and transistors...no longer a Hafler.

Could the wacky bias be a bad trimmer pot?

If it's a kit build, I would check all those wire/eyelet connections, too.

 

[z-adamson]

Here: http://www.hafler.com/pdf/archive/DH-220_amp_man.pdf

Oops I mean: http://www.hafler.com/pdf/archive/DH-200_amp_man.pdf

Scroll down to page 15 for transistor parts list

I really like the idea of looking at part numbers on the individual components. Who knows if a production change was made after the manual was printed. Problem is, many of the transistors that I see on the boards have no numbers.

 

[z-adamson]

Replacement boards and transistors...no longer a Hafler.

Could the wacky bias be a bad trimmer pot?

If it's a kit build, I would check all those wire/eyelet connections, too.

The pot seems fine. The circuit responds to turning of the pot as is should, but then an hour later, the bias will drift wildly.

 

[UncleBingo]

The musical Concepts mods (and the other ex Hafler employee mod kit) improve performance markedly from stock.

 

[z-adamson]

It is all covered here: http://www.diyaudio.com/forums/solid-state/31131-hafler-dh-200-220-mods.html

Take it to whatever level you want. The Musical Concepts mods when all of them are maxed out will take the amp to a very high level able to compete with a bunch of much more expensive amps. But you can do a lot just getting the list of mods done on these amps from the DIY thread. Enjoy, check back when you get done reading that. I'm about half done doing a list I put together from that thread.

I am mainly after restoring it to stock form. Not into hot-rodding it, not now anyways.

 

[z-adamson]

(and the other ex Hafler employee mod kit)

Qua-co?

 

[UncleBingo]

I really like the idea of looking at part numbers on the individual components. Who knows if a production change was made after the manual was printed. Problem is, many of the transistors that I see on the boards have no numbers.

The PC-6 parts location diagram with part numbers is on page 13.

 

[z-adamson]

The PC-6 parts location diagram with part numbers is on page 13.

Understood.

I have had problems with parts lists in service manuals being inconsistent with what was installed on the boards before and as such I try to rely on part numbers on the components first, and the manual last.

 

[Blue Shadow]

That said, has anyone here done a restoration using original boards?

Is there a mouser parts list out there?

I am mainly after restoring it to stock form. Not into hot-rodding it, not now anyways.

The link was a response to your thread starting question. Yes, some have done a restoration on the original boards and those guys have documented it on the DIY thread. No there is not a mouser list out there but it is simple to put together, not many parts.
The thread talks about using better quality parts on the original design and them doing some changes to improve the original amp. You can skip all those changes and look at what is recommended as upgraded components. Hafler gear it made to a price point, putting in better components is not hot-rodding the amp. But since you don't seem interested in learning about how to do this improvement, just replace all the electrolytic caps with the same thing and call it a day. If they amps work, that is all you need.

 

[z-adamson]

The link was a response to your thread starting question. Yes, some have done a restoration on the original boards and those guys have documented it on the DIY thread. No there is not a mouser list out there but it is simple to put together, not many parts.
The thread talks about using better quality parts on the original design and them doing some changes to improve the original amp. You can skip all those changes and look at what is recommended as upgraded components. Hafler gear it made to a price point, putting in better components is not hot-rodding the amp. But since you don't seem interested in learning about how to do this improvement, just replace all the electrolytic caps with the same thing and call it a day. If they amps work, that is all you need.

The thread is titled "hafler dh200 dh220 mods" and I did glance through the beginning of the thread and it sure did look like hot rodding to me. You are right, I am not interested in learning about that..............at the moment.

I didn't read far enough into it to see folks documenting their restoration of the original boards. I will look for that.

 

[Blue Shadow]

No one "Restores" the original board.
If they are restoring the unit they change the electrolytic caps, those "hot rodders" will use film caps as appropriate as a film cap is better in every way and won't need to be replaced.
If they have an issue with DC Offset they change the differential pair.

Other than that there isn't anything to do to restore these amps.

Changing anything else would be hot-rodding the amp.

 

[sfox52]

AK member "battradio" provided me with some matched transistors for a DH 200 a couple years back, he might still offer that service. At the least you should replace the 10 uf electrolytic input cap with a film cap- I think I used a 2.2 uf.