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Thread: Hafler amp problems

  1. #1
    Senior Member still4given's Avatar
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    Hafler amp problems

    I hope it is OK to ask this here. I'm using Hafler power amps right now. I've got two of them not working properly. Took one in to a tech and he told me the power transformer was bad and that they were NLA. I paid him for his diagnosis and took the amp home. I measured DC voltage across the two big caps and I get 67v+ on the one side and 42v- on the other. The other P230 reads 42v+ and 42v- on it's two caps. So, thinking he is right I search around and find a guy (soundvalves) who has two NOS power trannies. Great! I buy them. I get them yesterday and proceed to install one. Get it all installed and power up and measure voltage. No change. SO now I start unhooking things and take measurements on my good amp and the one I've just installed the tranny in. I've got 47VAC coming out of both leads on the tranny on the P230. 44VAC on each lead of My DH-200 which is in working condition. I check the DC voltage coming out of the bridge rectifier and I'm getting 67VDC+ and 44VDC- on the P230. The DH-200 read 60VDC+ and 60VDC-. Could it be my bridge rectifier? My other P230 reads about 44VDC+ and 44VDC-. Is this a common place for things to go bad?
    Thanks, Terry

  2. #2
    Norbert
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    Question about your P230

    Hi Terry,

    what is your P230 rated? So far I don't know this model. But what I get from your description is that the positive voltage rail is much too high (more than 20 Volts!). What are the offset voltages at the outputs of the bad P230? Does it change when you connect a dummy load (e.g. 8Ohm resisitor) Do you have a schematic?

    Regards,

    Norbert

  3. #3
    PSS AUDIO
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    Re: Hafler amp problems

    Originally posted by still4given
    ... I've got 47VAC coming out of both leads on the tranny on the P230. 44VAC on each lead of My DH-200 which is in working condition. I check the DC voltage coming out of the bridge rectifier and I'm getting 67VDC+ and 44VDC- on the P230. The DH-200 read 60VDC+ and 60VDC-. Could it be my bridge rectifier? My other P230 reads about 44VDC+ and 44VDC-. Is this a common place for things to go bad?
    Thanks, Terry
    Hi,

    It seems that you have a bridge problem as 44AC goes for 66DC DC=ACx1.414)!

  4. #4
    Senior Member still4given's Avatar
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    Thanks you guys, you're the best!

    I'll look for one on Monday. Man, I just spent $140 on two trannies on the word of that tech. Gotta pay to learn I suppose. Maybe I can sell the one I didn't install.

    Blessings, Terry

  5. #5
    PSS AUDIO
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    Originally posted by still4given
    Thanks you guys, you're the best!

    I'll look for one on Monday. Man, I just spent $140 on two trannies on the word of that tech. Gotta pay to learn I suppose. Maybe I can sell the one I didn't install.

    Blessings, Terry
    What kind of a bridge is it?

    A moulded one, or made of 4 diodes?

    Whatever, I can provide you those parts if you have troubles getting them.

  6. #6
    Alex Lancaster
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    Smile

    Terry:

    Look up part # 050-060 at partsexpress, 400V, 25A, $2.50.

  7. #7
    Senior Member still4given's Avatar
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    Hi guys,

    I believe it what would be called moulded. It says KBPC2502 on the side of it.

    You can see the specs here.

    Since it appears that both amps have the same problem, I 'm wondering if I should maybe replace it with something better. Any suggestions?

    Thanks, Terry

  8. #8
    RIP 2009
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    Originally posted by still4given
    Since it appears that both amps have the same problem, I 'm wondering if I should maybe replace it with something better. Any suggestions?
    If you lke Haflers, there are quite a few on eBay.

    John

  9. #9
    Senior Member still4given's Avatar
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    Hi John,

    Yes I know there are a few Haflers on ebay. I keep my eyes open there for them.

    I don't think I worded that right. I'm wondering about replacing the bridge rectifier with something else, not the amp. I would love to get these working again. I have found the stock rectifiers but I'm thinking, since I aready have two amps with blown retifiers, that maybe they are not the best design for this amp. Just thought maybe someone knew of something better to put in there, rather than the original designed bridge rectifier.

    Blessings, Terry
    Last edited by still4given; 10-04-2004 at 06:36 AM.

  10. #10
    Alex Lancaster
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    Smile

    Terry:

    Are You sure the rectifiers are blown?

    If so, You might have a short circuit down the road, rectifiers donīt blow that easy.

  11. #11
    Senior Member still4given's Avatar
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    Originally posted by Alex Lancaster
    Terry:

    Are You sure the rectifiers are blown?

    If so, You might have a short circuit down the road, rectifiers donīt blow that easy.
    Hi Alex,

    No, I'm not sure. I really don't know much about electronics, but am trying to learn. I started digging deeper, when replacing the Power tranny didn't work. I do know that I get the same reading from the output terminals of the bridge rectifiers whether they are hooked up to the rest of the circuit or not. In other words, if I disconnect the wires from the output of the rectifier, it reads the same DC voltage as if it is connected. My logic tells me that if there was something shorted I should at least see some difference in voltage.

    It bothers me that I paid a repairman to check out my amp, and he told me that the problem was the power tranny. I now know that is was fairly simple to check the output of the tranny and see that it was OK. The output from the bridge rectifier is what is low. Just seems he should have checked tranny by itself. He told me he couldn't fix the amp because the trannies were NLA. It took a bit of searching for me to locate some and so when I did, I bought them because they are hard to find and not being made any longer.

    Anyway, the bridge rectifiers are inexpensive so it seems like it will be worth a try at least. If that doesn't fix it, I suppose I'll have to find another repairman to look at them. It's getting to the point now that I could have bought something else with the money this is costing me, but I am learning some things so I am going to try and stick it out.

    Blessings, Terry

  12. #12
    Alex Lancaster
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    Smile

    As You say, the rectifiers are cheap, that Pexpress has more capacity than You need, and for $2.50, what the heck; when You put them in try them without connecting the output, if OK, hook them up and see if they overheat, You shoud be able to touch the heat sink and not burn Your finger, if You smoke them, the problem is possibly a shorted output (power) transistor.

    Good techs are hard to find anywhere in the world.

    Good luck!

  13. #13
    Senior Member still4given's Avatar
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    Is there an easy way to tell if an output transistor is shorted out? Can I check it with a multimeter?

    I think I can still get some NOS MOSFETs from the same guy I bought the trannies from. Hitachi doesn't make them anymore. There is a manufacturer in England who is making replacements.

    Blessings, Terry

  14. #14
    Alex Lancaster
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    Smile

    Terry:

    I think You need another tech.

  15. #15
    RIP 2011 Zilch's Avatar
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    Troubleshooting

    Click the multimeter over to AC volts to measure the ripple at the bridge rectifier output.

    Oscilloscope will show you what's actually going on with the rectification/filtering.

    If the DC output is low, either it's not delivering, or something is loading it down. Remember that transformers have impedance. Heavier load = lower output voltage.

    If the rectifier is OK but hot, it's load. The culprit is likely to be overly warm, too, unless it's shorted.

    Buyin' stuff and subsistuting is not the answer. Follow the current path to the problem....
    Last edited by Zilch; 10-04-2004 at 02:02 PM.

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