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Thread: Hafler amp problems

  1. #16
    Senior Member still4given's Avatar
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    OK, here's what I found. I changed out the bridge rectifier. When I installed it, I left off the output wires so I could get a reading on it with no load. The VAC coming from the transformer is 47.4 on both sides. The output from the rectifier is 19.5VAC and 42.3VDC each side. When I connect the wires to the outputs but with the wires disconnected from the Large Can capacitors. I get 44VDC+ on the + side and 43.9VDC- on the minus side. Then, when I bold down the wires to the Caps I get 67VDC+ and 44VDC-. Are the can capacitors designed to raise the voltage? My DH-200 reads 60VDC on both sides. Maybe the caps are bad.


    One MOSFET seems to get warmer than the rest so maybe it is bad. I don't know how to check them.

    Anyway, I would think that if there was a short downstream that I would see a big difference when i connected it, but I don't.

    The amp has a buzzing sound when hooked up to speakers. It plays but distorted. When I hook up the Positive cab I also get a low hum. It doesn't really sound different whether I have the big caps hooked up or not. Make me think there is something wrong wit the caps.

    Wish I had a good tech around. It's obvious the this one didn't know what was wrong with the amp.

    Any more help you guys can muster will be greatly appreciated.

    Blessings, Terry

  2. #17
    RIP 2011 Zilch's Avatar
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    Troubleshooting

    I trust you know you are working with potentially lethal voltages here. 60 VDC is considered dangerous, albeit not terribly so. Don't short out those capacitors with your tongue....

    The 19.5 VAC you read coming out of the bridge before you connect it to the filter capacitors (cans) is the "ripple" your meter is reading, over and above the 44 Volts it reads as the unfiltered DC. Note that your meter is not designed to read the unfiltered DC it is seeing there, so the readings are only approximate. Once attached to the filter capacitors, the filtered DC will approach the sum of the two, i.e. 64 volts (or more, apparently, in your case,) as the capacitors do their "job" of accumulating and storing the energy.

    You want to measure the VAC remaining with the bridge output connected to the capacitors. I am guessing that you'll find hardly any on the 67VDC+ side, but the same 19.5VAC on the 44VDC- side, indicating that either a) the filter capacitor on that side is not working, or b) something is substantially loading down that side. The hum (60 Hz?) in the speakers indicates that the power supply filtering is not working.

    So, confirm the VAC measurements on the filtered supplies, and if as above, I'd bet you need to replace that capacitor. I'd replace them both with identicals, if available, probably. Read the manufacturer, type and values and inquire here for substitutes, if necessary. Provide dimensions and pics, as well. Can you still get parts from the manufacturer?

    Does anybody believe I'm giving bad advice here? If so, don't be shy; jump aboard! We don't want to smoke this amp....
    Last edited by Zilch; 10-04-2004 at 07:14 PM.

  3. #18
    Senior Member still4given's Avatar
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    Alright! Now we're getting somewhere. I have two of these amps. The other one is reading only 44VDC or so on both sides. Like I said, there is almost no change whether the wires are attached the caps or not. My DH-200, which uses the same tranny, caps and bridge, is reading just over 60VDC per side and it plays perfectly.

    Another thing I noticed is that when I attach the wires to the caps while playing there is a small arc on the cap that is putting out 67 VDC but none that I can see when connecting any of the other three, that are putting out the 44VDC or so. So does this sound like bad caps? I'm not sure if Hafler still makes these or not , I will check. I'll try to take some pics and post them and see if I can read writing on the side of the caps.

    I can't tell you how much I appreciate this. Not just because I want to get my amp working, but I realy feel like I starting to grasp what is going on in here.

  4. #19
    Senior Member still4given's Avatar
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    OK, I did some acurate measurments. Here they are;

    Right cap> 65.3VDC, 0.0VAC
    Left cap> 42.6VDC, 19.8VAC

    Looks like you pegged it.

    The cap reads;

    EL CAP
    CER 103
    +10000MFD 75VDC
    85C USA 8839





    Blessings, Terry

  5. #20
    RIP 2011 Zilch's Avatar
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    Originally posted by still4given
    Another thing I noticed is that when I attach the wires to the caps while playing there is a small arc on the cap that is putting out 67 VDC but none that I can see when connecting any of the other three, that are putting out the 44VDC or so.
    That's because that capacitor is working. When you first touch the lead to it, it is uncharged. The little spark is because it's taking in energy to store.

    Take the same VAC readings on the other amp, capacitors attached. I'm betting, if the problem is the same, you'll see the same ~20VAC ripple. That one hums too, and plays distorted? [You ain't usin' nice JBL's to test with, I trust....]

    Now, we gotta find replacement capacitors. What's holdin' them caps in there, just the strap going from + to - on them in the middle? You want the same capacitors, physically, so they fit in the same space. Check Parts Express, Hafler Service, Google. Similars seem to be around $20. I've found Sprague @ 2" X 4.25" and Mallory @ 2" X 3.125" or 4.125" no El Caps, tho, yet....

    Here, for example.

    Ummm, measure with a PLASTIC ruler.

    Google says: Capacitor Address. - J. Kom-Tek, Division of El Cap. 116 Depot Street. Elgin, TX 78621-2614. USA. Tel: 512-285-5255. Fax: 512-285-5158. Type: Aluminum. If that's them, they can tell you who their distributors are, and whether they still make these particular ones.

    Last line there is the date code, most likely. If so, yours were made in ithe 39th week of 1988, i.e., 16 years ago....
    Last edited by Zilch; 10-05-2004 at 10:05 PM.

  6. #21
    Alex Lancaster
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    OK Terry:

    One of the caps is bad, but You should change both, You got the 10,000, the voltage and the 85 Celsius temp, or higher, any brand will do, but I would use new ones, if You get them cheap enough, check the voltage without connecting to the next stage, You should be getting +-60VDC and almost zero VAC; If You have 2 bad amps, try the 2 best caps on one amp, maybe You´ll get away with it; I don´t know the price of caps up there, but they can be expensive.

  7. #22
    Senior Member still4given's Avatar
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    Now, we gotta find replacement capacitors. What's holdin' them caps in there, just the strap going from + to - on them in the middle?
    They have a strap type cradle that they sit in. If you look closely at the picture you can see the band at the bottom. It would be best if I could find one the same diameter as the one that are in there. If not, maybe the company that make the replacement cap also make a cradle mount to fit.

    I called the phone number fo Kom-tek. I got a disconnect recording.

    Another question. Does it hurt to go up in value if I can't find the exact ones? Say, 11000mdf or 100V? Are these values important?


    If You have 2 bad amps, try the 2 best caps on one amp, maybe You´ll get away with it; I don´t know the price of caps up there, but they can be expensive.
    I thought of that but there is only one cap between the two amps that shows 60VDC. The others are all down around 40VDC.

    Thanks for everything, I will measure when I get home and see if I can locate one that will work.

    Blessings, Terry

  8. #23
    Senior Member grumpy's Avatar
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    bad caps

    Another question. Does it hurt to go up in value if I can't find the exact ones? Say, 11000mdf or 100V? Are these values important?
    10% difference in value is not important (electrolytics usually aren't that close to begin with).

    Keep the voltage rating up though, to the mfg
    value or higher or you could end up wearing
    capacitor on your face (not good). Might keep
    in mind that higher voltage ratings will typically
    increase at least one dimension of the cap,
    assuming similar design & construction.

    Sounds like you're starting to have fun

    -grumpy

  9. #24
    Senior Member still4given's Avatar
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    Re: bad caps

    Originally posted by grumpy
    10% difference in value is not important (electrolytics usually aren't that close to begin with).

    Keep the voltage rating up though, to the mfg
    value or higher or you could end up wearing
    capacitor on your face (not good). Might keep
    in mind that higher voltage ratings will typically
    increase at least one dimension of the cap,
    assuming similar design & construction.

    Sounds like you're starting to have fun

    -grumpy
    I am enjoying the learning experience. I could have done without the expense of two trannies I didn't need.

    I'm not sure what you mean by
    Keep the voltage rating up though, to the mfg
    Could you explain that a little better?

    Thanks, Terry

  10. #25
    RIP 2010 scott fitlin's Avatar
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    Caps and voltage ratings!

    You can increase the cap as far as rated working voltage, but you cannot use a lower rated working voltage!

    If your caps are 85vdc, you go with 85, or higher. 100vdc will be fine! I dont think you need to go substantially higher than a rated working voltage of 100vdc!

    If you were to put a 65vdc cap in there, it could blow up! This is why you dont use a lower rated working voltage.


  11. #26
    RIP 2011 Zilch's Avatar
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    Voltage rating:

    Your caps are rated 75 WVDC, 75 Volts DC Working Voltage. Seems your amps are actually using them between 65 and 70 VDC, which is fine.

    BUT, if you buy replacements at, say, 63 or, worse, 50 Volt rating, to save a little money, they'll possibly blow up on you. Grumpy is cautioning you NOT to replace with capacitors having a lower voltage rating than 75 V. You could go higher, though, and get higher voltage rated caps, but those will likely be physically bigger and not fit.

    Regarding the capacitance, I agree that going 10% to 25% higher would not be a problem, but, once again, the can will probably be bigger, and they'll cost more. I would NOT, however, jump up to 15,000 MFD or higher, I don't think, unless Hafler recommends it, as that might stress other components. Respect the designer's component selection unless you know it to be faulty.

  12. #27
    RIP 2011 Zilch's Avatar
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    Re: Caps and voltage ratings!

    Originally posted by scott fitlin
    If you were to put a 65vdc cap in there, it could blow up!
    The forum is unanimongus on this issue, coast to coast and Mexico included! [An apparent rarity here.... ]

    Same thing will happen if you hook 'em up backwards, as well. Pay attention to the polarities, there....

    Another point: I note in reviewing the specs on these "Computer Grade" electolytics (commercial rating 85° C) that their lifetime is stated as 10 years. Typically, they last much longer, though. I'm guessing your amps were either environmentally stressed or unused for a long period for these to fail like this.

    I'm not familiar with El Cap, but both Mallory and Sprague (Vishay) are quality manufacturers. Mounding straps will likely come with the caps or are readily available.

    This may be premature; we don't yet KNOW that the caps are the problem, or the only problem, for that matter, but it's sure looking to be a good bet at this point....
    Last edited by Zilch; 10-05-2004 at 10:13 PM.

  13. #28
    RIP 2010 scott fitlin's Avatar
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    Electrolytics

    Its entirely possible the big power supply electrolytics are somewhat dried out from both use and age!

    If in fact the caps, or one of, is going bad, or just out of spec, I would replace them all!

    An easy way to see how your caps are is to borrow a capacitance meter, and measure the value of the cap. If you measure a value more than the + - 10% spec, you need new caps!

    However, at this point in time, not having the amp in my possesion, and from what I have read so far, I am not entirely sure the caps are the problem, or the entire problem!

    The caps in your power supply can be gotten, Mallory, or Sprague are both good! Shouldnt be that expensive either!

    If you were here, or close to NY, I would send you to my service center, they are crackerjacks, and could overhaul the entire amp for you!
    Last edited by scott fitlin; 10-05-2004 at 02:46 PM.

  14. #29
    Senior Member still4given's Avatar
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    Thanks for all the help guys! I ordered these.

    I am aware that this may not be the entire problem. I did feel one of the MOSFETs getting a little warmer than the rest. I guess I'll cross that bridge when I get to it.Do any of you know how I can test those transistors while I'm waiting? It there a way to test them with a multimeter? I wouldn't mind getting those ordered while I'm waiting for the caps, if I need them.

    Thanks again, Terry

  15. #30
    Alex Lancaster
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    WOW!, the Hafler Odissey!; Some inexpensive multimeters have a transistor checker, do You know anybody that knows how to use them?

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