ads 860mx

[mike49504]

im working on an ads 860mx 8 channel amp there is 4 power supplys in the amp the amp blows the fuse in like 1 sec for 1 of the power supplys but all the channels work perfect when i put a meter on the power supply fets on 1 of the power supplys i ave a crap load of ohms but when i put in on the power supply in question i have 1 ohm i checked all fets all diodes all mpsa56 and 06's everything is fine but i know i have a short somewhere wondering what else do i check amp has me stumpped

[1moreamp]

Check the toroid for shorting I would guess. If the fets read good and the diodes are OK, I start looking at the toroid and the PWM controller and drivers if there are any.

By the way do you still need the 9 gold pins you asked about ? I still need to pull them off the two boards but I got them near my bench now if your need is still there...

[mike49504]

anyone have a pic of the inside of this amp power supply section there looks like there is parts missing like diodes and how do u check the torriod if it is shorting sorry havent got back to u been very busy with work

[1moreamp]

Ni pics just seen a few dozen of these over the years, The pins are still here if you do need them....

[Perry Babin]

When you read 1 ohm on the power supply, which two points did you have your meter on?


About the only short circuit you can detect with a standard multimeter is a short from the primary to the secondary.


Does this amp have the 'bridging' speaker terminals directly connected to the secondary center tap of the power transformer for that channel (it would have 2 secondaries/transformer)?


I have photos of the M860. If they're close to the same amp, I may be able to help.

[mike49504]

i have the meter leads from the gate leg on 1 fets to the gate leg of the next fet and it reads 00.1 ohm on 2 sets of the fets i replaced them with new still the same reading go to the other 2 sets of fets and they read 20 to 30 ohms like i said it pops the fuse when powerd up so i pulled the diodes in it the fen16cts and the fep16cts powerd up the amp and it doesnt pop the fuse but still reads like a direct short on the 2 sets of fets and u said the speaker briding pins if i put meter lead on the speaker pin and the other on torriod it reads 1 ohm not sure if im doing that right and also the amp powers up and plays fine out off all 4 channels without the 4 fuse in the amp as soon as i put the last fuse in it pops in like 1 sec i believe all the power supplys are tied together since the amp powers up and works expect blowing 1 out of the 4 fuses any help would be greatly appericatd

[Perry Babin]

It may have 2 problems.

The first seems to be at the FETs. If you read 0 ohms between the gates of two parallel FETs (one of the two banks of FETs for a single transformer) and the gate resistors are 10 ohms, there's no way that anything beyond the gate resistors can be causing the short.

Pull the gate resistors and check the resistance between the gates of the two adjacent FETs. If it reads 0.0 ohms, double-check the traces and confirm that nothing is connected to the gates except the gate resistors. If there is no other connection, you have to find the short in the area of the FETs.

Do NOT power up the amp with the gate resistors removed. If, for some reason you must power it up with the resistors removed, short the gate of the individual FETs to their source with a resistor or a piece of wire.

[mike49504]

ill try to putt the resistors later today im gonna order some parts for another amp im working on but wondering whats a good cross for theese diodes fen16ct and the fer16ct thanks for the help

[Perry Babin]

MUR1620CTG and MUR1620CTRG

863-MUR1620CTG and 863-MUR1620CTRG if you're buying parts from Mouser. The CTRG is the equivalent of the FEN part.