Need repair info on Hafler DH200

[Freecrowder]

Can someone direct me to any threads on Hafler DH 200 repair.
RG

[djk]

diyAudio - Search Results

[sakis]

what is the nature of your problem ??? what is your skills regarding repairs ?
information like that is needed to get some advice

[Freecrowder]

I have very low volume out of both channels. It sounds pretty clean but mostly upper frequencies. Source is directly from cd player(2) so should be plenty loud. All fuses test good. Power supply is +/-60VDC. Looked at bias both sides were at ~450ma,both heatsinks warm to touch (Adj. bias to 275ma). These are old amps from friend and noticed this one has 1/4 phone jack as input connectors???
I have worked on many SS amps and Tube also. I have electronics degree and experience. I have the schematic.
Looks like all original caps. I did come across an older thread talking about "220 with tin can sound". That sounds very close to my problem. Did pull a couple of the output transistors and measured with Fluke DMM. Measured results would at one time look like shorted and remeasure and would look ok??? I'm assuming that if it biases though the outputs are ok?
Thanks for any help provided
RG

[sakis]

most of these amps due to quality of parts and age might have parts inside that drifted from origfinal values ... most of the times these are capacitors not especially the big ones but small, signal and feedback related

make a close inpection there is also a chance that values of resistors have drifted if the machine is exposed to extreme heat or moisture

Finally its been some models that had also wiring and soldering issues which will mean that absense of ground in certain places might cause a million complications

kind regards sakis

[UncleArt]

I have a TA1600 that I've relegated to the junk pile for the exact same reason...and because I have no desire to replace surface-mount devices.

The TA1600 used early SMD electrolytics on the PC board; when these dried up, it was as though someone put a big pad and a 1 K high-pass filter on the inputs of this thing.

If the DH200 is at all similar, you will likely find a few dried out small signal caps in the input/driver stages.

[djk]

"It sounds pretty clean but mostly upper frequencies."

Cap in the feedback loop to ground (C5) is dried out, replace.

It's usually 470µF, 6.3V~10V bi-polar.

http://www.hafler.com/techsupport/pd...00_amp_man.pdf

[sregor]

Look for bad grounds especially around the input area. A signal generator and a scope should tell you alot. Also, I believe there may be a bridge/mono switch. May be in the wrong position or dirty. Plus all the other good information already posted. Good luck with it.

[djk]

"Look for bad grounds especially around the input area."

Both channels behave the same, and they are on different boards.

Considering how the inputs have been changed to 1/4", he may or may not have an R45. That would mainly cause a ground loop problem, depending on what was done.

"I believe there may be a bridge/mono switch"

Not on a stock DH200, the DH202 bridging kit was hardwired. A DH220 bridging kit (DH222) did have a switch mounted inside the unit.

[wally5]

Originally Posted by Freecrowder

I have very low volume out of both channels. It sounds pretty clean but mostly upper frequencies. Source is directly from cd player(2) so should be plenty loud. All fuses test good. Power supply is +/-60VDC. Looked at bias both sides were at ~450ma,both heatsinks warm to touch (Adj. bias to 275ma). These are old amps from friend and noticed this one has 1/4 phone jack as input connectors???
I have worked on many SS amps and Tube also. I have electronics degree and experience. I have the schematic.
Looks like all original caps. I did come across an older thread talking about "220 with tin can sound". That sounds very close to my problem. Did pull a couple of the output transistors and measured with Fluke DMM. Measured results would at one time look like shorted and remeasure and would look ok??? I'm assuming that if it biases though the outputs are ok?
Thanks for any help provided
RG

Hi, what were your DC offset readings.