Hello people! I'm new here! I've been reading a little and I'm impressed by all your knowledge.
Anyways, I bought a Hafler dh200 (220v version) from this dude. He said the right channel blew his speaker, but that the left channel was good. His theory was that the amp was sending current in the right channel that was damaging to his speaker.
I opened it up and saw that one of the two 5A fuses on the right channel was popped. The main fuse was good (although it was a 5A slo-blo when it should be 2.5A since this machine is wired for 220V and not 110V).
I also noticed that the speaker fuses was 5A and not 2A as some suggest is safer, obviously. These were intact.
Now to my questions;
Do I just change the broken fuse and the speaker fuses to 2A from the 5A and try this baby out? Do I risk damaging my Tannoy pbm speakers? Can the dude be right in that the amp blew his speakers? Then why were the speaker fuses intact?
I dont get it (not much knowledge of this stuff) and don't want to break my fantastic (hey, it's all I got) speakers, although I don't see how I could.
Would you please help mewith your thoughts? Thanx friends!
Hostarn
Anyways, I bought a Hafler dh200 (220v version) from this dude. He said the right channel blew his speaker, but that the left channel was good. His theory was that the amp was sending current in the right channel that was damaging to his speaker.
I opened it up and saw that one of the two 5A fuses on the right channel was popped. The main fuse was good (although it was a 5A slo-blo when it should be 2.5A since this machine is wired for 220V and not 110V).
I also noticed that the speaker fuses was 5A and not 2A as some suggest is safer, obviously. These were intact.
Now to my questions;
Do I just change the broken fuse and the speaker fuses to 2A from the 5A and try this baby out? Do I risk damaging my Tannoy pbm speakers? Can the dude be right in that the amp blew his speakers? Then why were the speaker fuses intact?
I dont get it (not much knowledge of this stuff) and don't want to break my fantastic (hey, it's all I got) speakers, although I don't see how I could.
Would you please help mewith your thoughts? Thanx friends!
Hostarn
blown power supply rail fuses mean that the output devices on that channel are shorted........ if you value your speakers DON'T connect them to this amp until that channel is repaired. speaker fuses generally aren't as fast as transistors and voice coils at blowing. also, somebody may have substituted slow-blow (type T) fuses for fast-blow fuses (type F), type T fuses should not be used as speaker fuses, but as power supply fuses, because they can handle the surge current of charging capacitors.
your output devices definitely need to be replaced, possibly even the voltage amp transistors, and a few resistors and diodes.
if you have little or no electronics experience, i would recommend that you take it to a tech that has audio experience. if you want to learn, maybe you could have him walk you through the troubleshooting, parts replacement, testing and adjustments. most amps have a lot in common in the way they work, and it's usually a matter of somebody having the expertise and the patience to teach you.
your output devices definitely need to be replaced, possibly even the voltage amp transistors, and a few resistors and diodes.
if you have little or no electronics experience, i would recommend that you take it to a tech that has audio experience. if you want to learn, maybe you could have him walk you through the troubleshooting, parts replacement, testing and adjustments. most amps have a lot in common in the way they work, and it's usually a matter of somebody having the expertise and the patience to teach you.
I got to tell you, I tried it out after I changed the blown fuse and the speaker fuses.
As you told me to value my speakers. I connected a pair of crappy pioneers that collects dust at my house. The amp worked great, no distortion or difference at all between the right and left channel. This is wierd don't you think?
Maybee I am wishfull thinking here but could it bee that the guy never changed the fuse that was broken and that's what made the amp working strangely, it was after all the fuse on the right side. And the reason why his speakers blew was that he used 5 A speaker fuses instead of 2A and that the main fuse was 5A sloblow instead of 2.5A sloblow?
As you told me to value my speakers. I connected a pair of crappy pioneers that collects dust at my house. The amp worked great, no distortion or difference at all between the right and left channel. This is wierd don't you think?
Maybee I am wishfull thinking here but could it bee that the guy never changed the fuse that was broken and that's what made the amp working strangely, it was after all the fuse on the right side. And the reason why his speakers blew was that he used 5 A speaker fuses instead of 2A and that the main fuse was 5A sloblow instead of 2.5A sloblow?
Maybe his speaker blew, and the voicecoil somehow shorted and caused the amp to blow the fuse?
Anyway, Hafler now has manuals online, if you didn't get one with the amp:
http://www.hafler.com/techsupport/index.asp?ID=3
Anyway, Hafler now has manuals online, if you didn't get one with the amp:
http://www.hafler.com/techsupport/index.asp?ID=3
Well I've read my DC offsets and (with or without load) both channels reads between 80 and 120 mv, they begin at 500 when I hit the power button and quickly descends to about 100 mv. I mesured a few times and it's not always the same. The right channel once read 30 mv.
Just to make sure I did it right; I took a multimeter set to DC 200mv and put red and black to respective colours at my speaker outputs. Is that how you do it?
I suppose this meusurements are a bit much? What needs to be done? How come it works when I test it without the DC protection to kick in? And could someone explain what the DC protection really does?
Just to make sure I did it right; I took a multimeter set to DC 200mv and put red and black to respective colours at my speaker outputs. Is that how you do it?
I suppose this meusurements are a bit much? What needs to be done? How come it works when I test it without the DC protection to kick in? And could someone explain what the DC protection really does?
They are a bit high. Most likely this amp needs a bit of attention, probably a replacement of all electrolytic capacitors at least.
The DH200 doesn't have DC protection, it has a loudspeaker output fuse only.
If there's the possibility that the right channel is intermittently putting out DC then you should get the amp serviced, otherwise it'll do it again and cook your speaker.
The DH200 doesn't have DC protection, it has a loudspeaker output fuse only.
If there's the possibility that the right channel is intermittently putting out DC then you should get the amp serviced, otherwise it'll do it again and cook your speaker.
cheers man!
But what do you mean intermittenly DC? You mean a lot more than what I mesured?
Some say change capacitors others say change the transistors, what's the deal?
And once again, I can't understand why the speakerfuses shouldn't blow first? Granted when the guys speakers supposedly blew he had higher ampere than I do now.
I mesured my other old trusty system for fun. I got 80 mv left and -250mv right!!?? This is a system I have never had any problems with. What do you thunk of that?
Thanx again guys for explaining things to me!
But what do you mean intermittenly DC? You mean a lot more than what I mesured?
Some say change capacitors others say change the transistors, what's the deal?
And once again, I can't understand why the speakerfuses shouldn't blow first? Granted when the guys speakers supposedly blew he had higher ampere than I do now.
I mesured my other old trusty system for fun. I got 80 mv left and -250mv right!!?? This is a system I have never had any problems with. What do you thunk of that?
Thanx again guys for explaining things to me!
while those offsets (yes, that is the right way to do it) are a bit high, they are within the "normal" range. the reading of 500mV dropping down is normal, since you are charging the DC correction cap for that period of time.
even if you have a device open, the amp feedback will usually hold the offset within the normal range (usually, not always). with the power off and the power supply caps discharged, you should be able to check the output devices with an ohmmeter. compare one channel to the other. if you have any readings vastly different, you might find your problem. the center lead on each device is the drain, the left hand pin is the gate, and the right hand pin is the source. MOSFETs read a lot different than bipolar transistors, so you may want to test them out of circuit if possible. the gates should read open circuit to the other pins. the drains should read open circuit to the source in one direction (when the meter polarity matches the power supply polarity) and a diode drop in the other direction (MOSFETs have a "bulk" diode).
even if you have a device open, the amp feedback will usually hold the offset within the normal range (usually, not always). with the power off and the power supply caps discharged, you should be able to check the output devices with an ohmmeter. compare one channel to the other. if you have any readings vastly different, you might find your problem. the center lead on each device is the drain, the left hand pin is the gate, and the right hand pin is the source. MOSFETs read a lot different than bipolar transistors, so you may want to test them out of circuit if possible. the gates should read open circuit to the other pins. the drains should read open circuit to the source in one direction (when the meter polarity matches the power supply polarity) and a diode drop in the other direction (MOSFETs have a "bulk" diode).
to measure transistors you use the meter in diode test mode and measure from one pin to the other. testing MOSFETs can be tricky if you've never done it before. when testing the gate, the gate ends up with a charge on it that later affects the source-drain measurement, so it might seem like the device is shorted when it's not. if you know somebody with some electronics experience, i recommend you get them to show you how.
mhm, if I got it straight I put the multimeter in diode mode and put the meters negative thingy on the source. Then I put the meters positive thingy on the gate, then I move it to the drain. The meter should then read low. I then put a small cable between source and gate, while still connected with the meter which should now read high.
Is this a correct way to test the mosfets? I should test all 8 mosfets in the amp I suppose?
Is this a correct way to test the mosfets? I should test all 8 mosfets in the amp I suppose?
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