Yamaha M-4 in & out of protection - HELP?

bobrown14 said:
What do you replace the big ones with?

Cheers,

Bob
Click to expand...

Big ones..:D Due to the cap hold down cover you choices are limited to height and the metal cap shield limits you to diameter. The originals are lug style solder tabs.Which I have not been able to source. So..Panasonic "snap ins" from Digikey.IIRC 50mm X 80mm 22,000uf @ 100v..Originals are 18,000uf @ 75 vdc...A little increase in capacitance. :thmbsp:
 
Update....

Got my replacement T03 transistors - will be installing them tomorrow.

On an aside.... I just had to get another M series amp, I liked the M-4 so much a MINT M-2 came up on eprey BIN last week and I was able to take advantage of the 10% outage rebate - got a pretty good deal. So I've got a good replacement till I upgrade the M-4 with new transistors and after I get that going I will do the re-cap.

I'm using an C-80 pre which sounds Ok, best is DAD, not that impressed with the phono stage tho. I'm guessing it's also in need of a cap refresh - the pre was used by a DJ in it's prior life.

Man that M-2 is big. Same size as my Crown PSA-2 that it's sitting beside but with a much more impressive look. The unit is mint on the outside at least. VERY nice. The amp came packaged as good as it gets. No kidding - the guy that sold it to me works at some fishing reel company and it was packaged in new double boxed, fishing reel logo on the outside AND strapped, wrapped in large bubble wrap, packed to withstand a VERY large drop. I'll be keeping that box for sure.

Happy day,

Bob
 
M-4 new transistors

Ok I installed the new transistors and am going thru the setup for power supply (good at +- 65V)

Idling current (bias) good on left channel (15mV)

I'm not able to adjust the right channel -
turning VR402 has no affect on reading and I'm getting 0mV on my DMM.

What would I need to look at next ??

Thanks in advance for HELP!

Bob
 
Open emmiter resistors will get you unusually large bias voltage measurements. Bias doesn't adjust etc, you should look to shorted bias transistor and shorted voltage clampers (they'd be transistors or a stack of zeners an pn junction diodes).
 
avionic said:
R440,442,444,446 --.47 ohm (emitter)
As well as...
R462--470 ohm
R438--10 ohm
Click to expand...

Looks Like I found a bad fuse resistor FR402
marked on the board as - 25mA390 Ohm white resistor

Also another fused resistor is measuring open

FR408 - 85mA 330 Ohm

Where can I find replacements for those??

Bob
 
Wow..Best pull all those transistors and diodes that are linked to those fusistors..And check for shorts or broke down junctions.As far as replacements 2 watt metal film/oxide.
 
avionic said:
Wow..Best pull all those transistors and diodes that are linked to those fusistors..And check for shorts or broke down junctions.As far as replacements 2 watt metal film/oxide.
Click to expand...

Can give me a source for the correct resistor fusisitor?
Would these work?
Mouser 594-5083NW390R0J - 390 ohm 2 watt Vishay Metal Film
Mouser 594-5083NW330R0J - 330 ohm 2 watt Vishay Metal Film


What do you mean by "broken down Junctions"? All the other resistors tested good cept for the 2 fusistors. I'll pull the transistors and test the diodes that link to the fusistors and test them.

Thanks,

Bob
 
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Okay.. finally go a little time and my solder station out. Replaced the fusistors and the 4 main power transistors and ...... VOILA, Music - yeah u right!

Hooked back up to my Infinities and they sound a little better with the M4 than my Crown... I think a less colored sound.

I had to adjust the gain on the re-built side down a tad - seems to have a little more output than the previously good side. Very slightly more output but enough to notice. Is that anything I need to be concerned with?

So all is good... moving on to my dead M-2.

Thanks for everyone's input - specially Avionic. :beer:

Cheers,

Bob
 
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