View Full Version : Repairing a Hafler MOSFET amp.

M Jarve
06-01-2006, 06:45 PM
I could not resist. A 150WPC Hafler designed power amp for $40. It is a Digitech G300 amp.

One channel is blown on it (blows fuses at power up) and two of the 4 output MOSFETs in that channel have scorch marks. Visually, that is the only problem.

My plan, such as it is, is to completely remove the DOD board (some buffer and “Presence” circuitry, trim-controls, as well as ¼-inch speaker jacks), and install some input jacks and new binding posts on the rear panel.

I am quite unfamiliar with MOSFET amps, and am not quite sure what to look for in repairing it. Should I start with replacing the output MOSFETs and go from there? Is there anything that commonly goes wrong with Hafler amps?

I’ll try to take some pics tonight too.

M Jarve
06-01-2006, 07:10 PM
It seems to use two pair of 2SJ161/2SK1057 per channel. It is one of each type that have the scorch marks, although the inner two measure like the "good" channel and have no scorch marks.

The bad MOSFETs have a DCR of ~12-ohms between the gate and drain, where as it is about 700k-ohm on the good ones.

Maybe it's just the outputs?

06-03-2006, 03:41 AM
Check all of the transistors and diodes on the board for shorts while comparing to the good channel. Go to the hafler site and download the manual. The manual will tell you how to set the bias.

06-03-2006, 05:17 AM
2SK1057 ComponentsQQddnZIndustrialQ20SuppliesQQadnZElectri calQ20Q26Q20AutomationQQcmdZExpressItem

2SJ161 ComponentsQQddnZIndustrialQ20SuppliesQQadnZElectri calQ20Q26Q20AutomationQQcmdZExpressItem

06-03-2006, 12:34 PM
Hey Glenn... I can't remember the numbers for the MOSFET output in the DH200... would these same people have those, by chance?

Thanks a bunch (got one here, we're trying to fix up)...