My old trusty DH-220 has lots of noise coming out of the right channel, static like and some pops, there is no bias current while the left channel is fine. There is voltage going to the final mosfets (60v) but not current.
Any thoughts on this?
Any thoughts on this?
Is your measured voltage to the mosfets at the drain? What are the source and gate voltages?
Any idea what could have caused the problem? Did it happen at turn-on, while messing around with speaker wires, etc?
On the PC19 board, the first thing I would check is Q9, but it could be many other things too.
Any idea what could have caused the problem? Did it happen at turn-on, while messing around with speaker wires, etc?
On the PC19 board, the first thing I would check is Q9, but it could be many other things too.
Could have been any of those reasons since I tend to tinker a bit more than I should.
Q9 was replaced with no change and I haven't checked the mosfets yet, I would hate to think one or more are blown but I'm starting to gravitate to that idea.
Q9 was replaced with no change and I haven't checked the mosfets yet, I would hate to think one or more are blown but I'm starting to gravitate to that idea.
service manual here: http://www.hafler.com/techsupport/pdf/DH-220_amp_man.pdf
Voltages at the points mentioned on page 12 will help find the problem. The mosfets are apparently quite robust and dont fail easily.
Voltages at the points mentioned on page 12 will help find the problem. The mosfets are apparently quite robust and dont fail easily.
jaycee... Im glad you mentioned page 12 with the voltage points in the man.
I will check and post results
Thanks.
I will check and post results
Thanks.
Checked the voltages on the MOSFETS and the good side reads very close to the manual, te good side reads very close to the specs on the manual,
The bad side...
D +61v D -3.5v
D +61v D -3.5v
D -61v D -3.5v
D -61v D -3.5v
Notice that all the D sides are -3.5v. Blown mosfets?
The bad side...
D +61v D -3.5v
D +61v D -3.5v
D -61v D -3.5v
D -61v D -3.5v
Notice that all the D sides are -3.5v. Blown mosfets?
If one transistor has failed, change them all ( not the priceless outputs of course). Really strange and higher than expected voltages can show up when you have a fault the damages all kinds of things. Don't trust the stated voltages that carefully as it depends on line voltage. These are very old, so it is time for recapping. Check R31 and R23 believe it or not. There is no such thing as a good pot, so check the bias adjustment resistor.
- Status
- Not open for further replies.