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Hafler P-500 Restoration
Hafler P-500 Restoration
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Old 16th June 2017, 07:34 PM   #11
mjstriker5 is offline mjstriker5  United States
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Hi phase, that would be awesome but That is probably in mono. We would probably get more than the stated 255 WPC running two speakers one each side for a total of 4 ohms.

Craig, thanks for the clever idea to short C6. I'll give it a try and see if it narrows down the problem.
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Old 16th June 2017, 09:20 PM   #12
mjstriker5 is offline mjstriker5  United States
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Craig,

I shorted C6 as you advised. I am now reading 0.440V at C6. If I am interpreting this correctly I should actually have close to 0V as the positive/negative rails are symmetrical and should cancel each other out. This also means I am missing -0.440V on the negative rail which is consistent with my previous readings. Only difference now is the bias has been bi-passed and is probably not responsible for my issues.

I also checked the other test points and everything is essentially spot on with the schematic and equal in comparison to the negative/positive sides.

I am going to double check some resistors but I am putting my money on D13 or D14.

Thanks again for the tip on circumventing the bias. That seems to have saved me quite a bit of troubleshooting.
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Old 16th June 2017, 09:42 PM   #13
llwhtt is offline llwhtt  United States
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Make sure your diode polarities are correct. I'm pretty sure those networks are for protection and if good shouldn't affect anything at idle. In other words you can probably remove them for testing purposes.

Craig

What does the DC offset look like?

Last edited by llwhtt; 16th June 2017 at 09:59 PM.
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Old 16th June 2017, 10:29 PM   #14
mjstriker5 is offline mjstriker5  United States
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I replaced the !n4148 diode on both sides and double checked the 4 diodes because I thought maybe the polarities were off. Based on the screening they are OK. Didn't think of it at the time but I will double check the traces to confirm what is screened on the board in regards to polarity is consistent with the actual layout.

After replacement I am still getting +0.440V so I didn't change anything. I am going to check all the resistors again to see if any are off. They weren't before but at this point I might have missed something.

I did notice some slight differences in voltages at D8 and D7 away from test point E were different. D8 was -.642V and D7 was +0.617. I am going to finish replacing diodes but I can't imagine those values causing my problem.
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Old 16th June 2017, 10:36 PM   #15
llwhtt is offline llwhtt  United States
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If Q13 was fried what about R33?
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Old 16th June 2017, 11:05 PM   #16
mjstriker5 is offline mjstriker5  United States
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R33 checked out fine. It was 216 ohm and was specified to be 220.
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Old 16th June 2017, 11:39 PM   #17
llwhtt is offline llwhtt  United States
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What's the voltage across R29 & R30?

Craig
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Old 16th June 2017, 11:44 PM   #18
kct is offline kct  Canada
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Hafler P-500 Restoration
Quote:
- Q8/Q11/Q12/Q13 with exact replacements (one was fried so I did all of them)
Which one was fried ?

Failure mode CE open ?
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Old 17th June 2017, 01:31 AM   #19
mjstriker5 is offline mjstriker5  United States
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R29: -1.5V (this is the same but positive on the other side)
R30: -1V (also the same but positive on the other side)

I got this value by subtracting each leg in relation to ground

Q13 was the dead transistor. The base leg was fried off and fell out when I desoldered the lead.

Last edited by mjstriker5; 17th June 2017 at 01:39 AM.
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Old 17th June 2017, 01:42 AM   #20
phase is offline phase  United States
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Watts Per Channel...
Rms was around 325@8ohms or something way more than the 255 listed in the literature.
Ok, you made me go find it again;
http://www.hifi-classic.net/review/h...h-500-287.html

Last edited by phase; 17th June 2017 at 01:50 AM.
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