hafler dh200 blew speaker?

[hostarn]

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

[unclejed613]

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.

[hostarn]

thanx for your input! Not good news though. I forgot one thing, the dude said that the right channel of the amp started working great from time to time. Isn't that strange?

[unclejed613]

i've seen dh200 amps burn open the shorted device and continue working almost normally, except that on 4 ohm loads it would distort.

[hostarn]

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?

[hostarn]

I mean, if it now seems to work fine, no distortion or anything what could go wrong?
Since I now have 2 A speaker fuses I'm good right? Is there anything else than Ampere that could hurt my speakers? Voltage? How do I mesure that? A multi meter in the speaker output?

[unclejed613]

if you have a device burned open, you won't notice anything except DC offset (about 1V or so), or distortion with 4 ohm loads, or the two channels don't sound the same. if you drive it hard you might really notice it as a difference in sound between the two channels

[hostarn]

ok, thank you! I will read up on how, and then I will mesure the DC offset!

[dangus]

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

[hostarn]

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?