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M100...another jewel that was fiddled with

Posted: Mon Aug 27, 2018 5:54 pm
by wesleyb420
So on the heels of getting the M50 working, i opened up the M100 to see what the issues were with this guy.

1. Input Caps...replaced them and one was bad. Replaced the bad one.
2. Resistor mod...done very badly by the PO. I tried to repair but the resistors tested good. I will mark that as good, just horrible looking.
3. Dim green LED...It is dim but it is on. Not really sure what this means but my guess is that something is wrong.

Any suggestions on where to start? the M50 was straightforward enough and had not been touched...this one has been messed with and I dont know where to start troubleshooting. From my testing of the IRFz44 transistors, they seem open.

Thanks again for the help.

Re: M100...another jewel that was fiddled with

Posted: Tue Aug 28, 2018 10:56 am
by Silverhorse
pictures of the board?
maybe the amp pulls to many current so you have a voltage drop.
Can you measure how many amps it uses? What is your power source?

Re: M100...another jewel that was fiddled with

Posted: Tue Aug 28, 2018 11:00 am
by wesleyb420
pictures of the board? - I will post some tonight...be warned...it's bad.
maybe the amp pulls to many current so you have a voltage drop. - Possible, see below
Can you measure how many amps it uses? What is your power source? I am using a computer power supply which "should" supply 12v 18A. I know it is on the low side, but the amp still should start, right? I didnt even think to measure how many amps it is pulling, ill check that tonight as well.

Re: M100...another jewel that was fiddled with

Posted: Tue Aug 28, 2018 12:43 pm
by Silverhorse
12v 18A power supply is ok for testing.
if the amp uses more than 3 amps idle than something is wrong.
is the red LED also lighting up?

Re: M100...another jewel that was fiddled with

Posted: Tue Aug 28, 2018 4:14 pm
by wesleyb420
No red light, just an extremely dim green light.

Re: M100...another jewel that was fiddled with

Posted: Tue Aug 28, 2018 5:08 pm
by wesleyb420
Draw at idle is 4.7a. Red light turns on then goes off normally during startup.

Re: M100...another jewel that was fiddled with

Posted: Tue Aug 28, 2018 5:32 pm
by wesleyb420
Here are some photos. Let me know if they are too crappy.

Re: M100...another jewel that was fiddled with

Posted: Wed Aug 29, 2018 1:44 am
by ttocs
have you checked the voltage on the led yet?

Re: M100...another jewel that was fiddled with

Posted: Wed Aug 29, 2018 10:42 am
by wesleyb420
Yes, it is 1.75V

Re: M100...another jewel that was fiddled with

Posted: Wed Aug 29, 2018 12:10 pm
by ttocs
I am not a pro but that seems low. what voltage are the other leds reading?

Re: M100...another jewel that was fiddled with

Posted: Thu Aug 30, 2018 9:32 am
by Silverhorse
seems like a bad connection somewhere. Maybe a bad via.
this is a difficult one...

Re: M100...another jewel that was fiddled with

Posted: Thu Aug 30, 2018 4:11 pm
by wesleyb420
This may sound silly but would the vias for the resistor "mod" that was done, cause this? I can take them out along with the caps to check everything.

Should i/How can i rule out the transistors? I have seen ways to test them but I have no experience with it. The PO said that 4/6 power side transistors were bad but he also said that this board had not been messed with.

Re: M100...another jewel that was fiddled with

Posted: Fri Aug 31, 2018 10:36 am
by Silverhorse
I'm not an expert, the experts are stil on holiday I think :(
What I would do:
- take out all the components that are not original ( the 4 white ressitors to start...)
- take out the 4 IRFZ 44 and test them individual when they are out
- take out the 6 PSU caps
- take out other components that are looking not good
- when they are removed, remove all the solder with desolder braid or desolder pump
- check that you have connection between both sides of the PCB (when the via is pulled out you have no connection)
- if you have a bad via restore them (you can find info on this forum how to do this)

- put the 4 resistors back in
- put back the other components that you have removed, when they are discoloured or burnt replace them with new
- put the 4 IRFZ 44 back in (if you have new FET's in stock, use them)
- put back 1 capacitor
- put back the heatsink on the board (never power up without heatsink)

- power up the amp back up, use a 10 amp fuse
- when it powers up fine you can place the other 5 PSU caps

Re: M100...another jewel that was fiddled with

Posted: Fri Aug 31, 2018 1:08 pm
by wesleyb420
Where can I find the irfz transistors?

Whats a solid procedure to test the transistors?

I had to do a few via holes on the m50 so I’m familiar with that process...good call on testing them.

Re: M100...another jewel that was fiddled with

Posted: Fri Aug 31, 2018 2:08 pm
by ttocs

Re: M100...another jewel that was fiddled with

Posted: Fri Aug 31, 2018 5:27 pm
by wesleyb420
The guy in that video says his method will not work with fets...I have not found a swell video yet.

Re: M100...another jewel that was fiddled with

Posted: Fri Aug 31, 2018 6:28 pm
by ttocs

Re: M100...another jewel that was fiddled with

Posted: Sat Sep 01, 2018 11:34 pm
by Silverhorse

Re: M100...another jewel that was fiddled with

Posted: Fri Oct 12, 2018 9:08 pm
by wesleyb420
Replaced the 4 irfz44 and she is back in action!!! Thanks guys!!!!!