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Old 8th June 2012, 05:15 AM   #1
john65b is offline john65b  United States
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Default Hafler P3000 -67V on output

Hey all,

I have a Hafler P3000 amp that has the full neg rail on outputs (-67V).

Looking at the schematic, I can't see a real way to get -67v on the red speaker out referenced to black, unless that C5 (6800uf, 80V) cap is bad.

Other channel working fine.

The gain / volume pot on this channel was damaged (bent / disconnected from PCB), and has been replaced. did not seem to have any effect on the neg rail DC on outputs. Also has the Thermal LED lit... any ideas?

I know these transnova cap coupled output amps a a bit goofy, like the Acoustat TNT amps...
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Old 8th June 2012, 05:42 AM   #2
odeer is offline odeer  Australia
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Is one or more of the output fets shorted/ failed in the suspect channel?

is it worth pulling them out individually and testing them.
This is how I found dead mosfets in my ALEPH 5 some time ago...

George
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Old 8th June 2012, 01:11 PM   #3
john65b is offline john65b  United States
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Yes, but to get neg rail on the Positive speaker out per the schematic - seems to me only way is to go through the bad cap. If one of the outputs (pin 1 to 3) were shorted,the Fuse would blow,correct?

Don't mean to disagree, but these Transnova's are a goofy design...
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Old 8th June 2012, 01:44 PM   #4
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is that 67V with a load attached? without a load it is possible that the caps float up to the rail if there is a shorted output. with a load that should stay at "0" volts. unless the cap is shorted like you said.
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Old 8th June 2012, 02:10 PM   #5
john65b is offline john65b  United States
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Didn't think of that...I have a 8 ohm dummy load I can throw on the amp outputs. I also will check the working channel for 67v unloaded....I don't think the output fets are bad, and they aren't cheap...
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Old 8th June 2012, 02:53 PM   #6
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It wouldn't even have to be an 8 ohm load... a few kOhms or so would also do. Excessive leakage (up to eventually shorting out) isn't unusual in electrolytics showing their age.
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Old 8th June 2012, 05:17 PM   #7
john65b is offline john65b  United States
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Why is it after days of putzing around on various problems I final post it here and figure it out within hours of posting?

When I replaced the bashed in potentiomter, I miss-soldered the wiper connection, and was not connected to pin 3 of U2...all good now.
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