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 Post subject: M44 repair question
PostPosted: Wed Aug 01, 2018 4:13 am 

Joined: Sat Aug 06, 2011 1:18 am
Posts: 48
Hello everybody

for the moment i'm repairing a M44 amp. It has blown powersupply fets and other issues.

There are 4 IRFZ44 fets with their gate resistors of 100 Ohm. If you look closely you can see that there are only 3 resistors of 100 Ohm the most left one measures 51 Ohm. Is this normal? (it looks original)

there is also one diode on location CR13. It's close to cap C32. Does anybody know what the specs are of this diode?


Attachments:
irfz44 M44.JPG
irfz44 M44.JPG [ 201.53 KiB | Viewed 203 times ]
diode CR13.JPG
diode CR13.JPG [ 263.74 KiB | Viewed 203 times ]
gate resistors.JPG
gate resistors.JPG [ 210.98 KiB | Viewed 203 times ]
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 Post subject: Re: M44 repair question
PostPosted: Wed Aug 01, 2018 7:50 am 

Joined: Tue Nov 06, 2012 9:30 pm
Posts: 63
Silverhorse wrote:
Hello everybody

for the moment i'm repairing a M44 amp. It has blown powersupply fets and other issues.

There are 4 IRFZ44 fets with their gate resistors of 100 Ohm. If you look closely you can see that there are only 3 resistors of 100 Ohm the most left one measures 51 Ohm. Is this normal? (it looks original)

there is also one diode on location CR13. It's close to cap C32. Does anybody know what the specs are of this diode?
No, and its gotten hot which would probably indicate a failed transisor. The experts will chime in eventually but i see some heat damage there.

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 Post subject: Re: M44 repair question
PostPosted: Wed Aug 01, 2018 9:22 am 

Joined: Sat Aug 06, 2011 1:18 am
Posts: 48
there is also an output problem...

there are 4 x A1265 transistors and 4 x C3182 transistors, one A1265 is shorted. What is a good replacement for these?
is it OK to use two different complemantery transistors? Looks like this amp had no repairs before.


Last edited by Silverhorse on Thu Aug 02, 2018 3:27 am, edited 1 time in total.

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 Post subject: Re: M44 repair question
PostPosted: Wed Aug 01, 2018 10:21 am 

Joined: Sat Aug 06, 2011 1:18 am
Posts: 48
this is the one that is shorted...


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 Post subject: Re: M44 repair question
PostPosted: Wed Aug 01, 2018 5:13 pm 

Joined: Tue Nov 06, 2012 9:30 pm
Posts: 63
Im pretty sure there are 2 sets to deal with both halves of the waveform. Pm jacamb2, ericd, ttocs they seem to know what they are talking about.

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 Post subject: Re: M44 repair question
PostPosted: Thu Aug 02, 2018 3:32 am 

Joined: Sat Aug 06, 2011 1:18 am
Posts: 48
did some researche

Sanken 2SA1695
Toshiba 2SA1941

Are these OK? Which are the best?
when using these, are there other components to be changed?


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 Post subject: Re: M44 repair question
PostPosted: Thu Aug 02, 2018 3:41 pm 

Joined: Tue Nov 06, 2012 9:30 pm
Posts: 63
One of these guys has a parts list. Im not sure if its whitenoise or eric.

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 Post subject: Re: M44 repair question
PostPosted: Fri Aug 03, 2018 6:57 am 
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Joined: Sat Apr 19, 2008 11:57 pm
Posts: 1421
Location: Beaverton 48612
I use fjl4315/4215 or 2sc5200/2sa1943 pretty much on every PG amp that I repair. Most of the later models used these outputs (they are both the same part, different manufacturers, and are a significant upgrade for the early m series), they should require no modification to use in lace of the originals. You need to replace all the pairs though of you go to these transistors, they are quite a bit different from the originals. The Sanken part you linked above should work fine s well, but unless you specifically want the brand I can't see much reason to pay the premium to get them. You still need to replace all compliments, so at the least the pnp/npn part on the bad channel, but I'd replace them all if you are changing to a different device from stock.

As for the gate resistors, that's not right, see below.


Last edited by Jacampb2 on Fri Aug 03, 2018 7:03 am, edited 1 time in total.


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M: M100, M44 for a custom amp project
Zx: Zx500, Zx450, Black Zx350
ZxTi: 4 Zx600Ti's, 1 Zx400Ti
Ti: 5 800.1's & 900.7 for a custom amp project. 1 1200.1, 1 1000.2
Tantrum: 2 1200.1's, 1 600.4, 1 500.2
XS: XS6600
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 Post subject: Re: M44 repair question
PostPosted: Fri Aug 03, 2018 7:03 am 
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Joined: Sat Apr 19, 2008 11:57 pm
Posts: 1421
Location: Beaverton 48612
The diode in question is a 15v zener, 1n5245b. R21-R24 gate resistors should all be 100R 1/4 flameproof or fusible.

The 51R resistor does look like a factory part, my guess is that someone has seriously fucked up this amp. The 51R resistors are used in the power amp section. Dollars to donuts you will find the wrong resistors in that section because someone clearly swapped one into this gate position.

Good luck,
Jason



_________________
M: M100, M44 for a custom amp project
Zx: Zx500, Zx450, Black Zx350
ZxTi: 4 Zx600Ti's, 1 Zx400Ti
Ti: 5 800.1's & 900.7 for a custom amp project. 1 1200.1, 1 1000.2
Tantrum: 2 1200.1's, 1 600.4, 1 500.2
XS: XS6600
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 Post subject: Re: M44 repair question
PostPosted: Sat Aug 04, 2018 6:47 am 

Joined: Sat Aug 06, 2011 1:18 am
Posts: 48
Thanks Jason for the info.

I've put 4 new gate resistors en 4 new irfz's in, now the power supply works!
The BJT's I need to order.

Do you think that the resistors are switched during the production of this amp? Could this be the reason that this amp failed?
Damn! than I need to find the other one...


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 Post subject: Re: M44 repair question
PostPosted: Sat Aug 04, 2018 10:39 am 
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Joined: Sat Apr 19, 2008 11:57 pm
Posts: 1421
Location: Beaverton 48612
It would have never passed qc like that. The fet with the lower gate resistor would have been pushed much harder than it's parallel part and it's compliment. Miss matched gate resistors normally cause ps fets to go off like popcorn. If one fails the failure cascades to the others in rapid order. Anything is possible, but I highly doubt it would have passed its birth check let alone 30 + years of use.

My guess is that someone was monkeying with the power amp, pulled some resistors and then forgot where they went...

Good luck,
Jason



_________________
M: M100, M44 for a custom amp project
Zx: Zx500, Zx450, Black Zx350
ZxTi: 4 Zx600Ti's, 1 Zx400Ti
Ti: 5 800.1's & 900.7 for a custom amp project. 1 1200.1, 1 1000.2
Tantrum: 2 1200.1's, 1 600.4, 1 500.2
XS: XS6600
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