Yamaha M-4

jhal

Titanium Bliss
Well, since getting the separates "bug" after getting a Yamaha CX-830 preamp and TX-350 tuner off of CL, I have been hunting for an amp. I Ebayed me an M-4 for what I consider a deal. It will need some Deoxit treatment according to the seller, the gain controls are noisy. I just hope it gets here in one piece, the seller seems to know proper packing. It should be here by Friday or Monday. Wish me luck.:thmbsp: Next thing will be to upgrade to a better tuner. This one is ok, considering the amount of radio I listen to, which isn't much. You can listen for an hour before the songs start repeating (or so it seems).
 
Well, since getting the separates "bug" after getting a Yamaha CX-830 preamp and TX-350 tuner off of CL, I have been hunting for an amp. I Ebayed me an M-4 for what I consider a deal. It will need some Deoxit treatment according to the seller, the gain controls are noisy. I just hope it gets here in one piece, the seller seems to know proper packing. It should be here by Friday or Monday. Wish me luck.:thmbsp: Next thing will be to upgrade to a better tuner. This one is ok, considering the amount of radio I listen to, which isn't much. You can listen for an hour before the songs start repeating (or so it seems).
Those gain pots are 30k jobs.The ones on my M-4 had cracked carbon pads. May still be able to get them from Yamaha if you need them.I'll keep the finger crossed on the deox-it for you.:yes: Otherwise that is a real nice amplifier.....
 

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Agreed, nice amp. I would have two, but UPS just picked up the damaged one from fleabay.
 
Agreed, nice amp. I would have two, but UPS just picked up the damaged one from fleabay.

You're scaring me.:sigh: I Just got the tracking #, my amp will be here on the 14th. Man I hope it is in good shape. I have had good luck so far, my 40 plus pound KA-801 got here all the way from Washington State in good shape (and we all know how fragile the switches are on them), the Yamaha is coming from Texas. I have talked to the seller and this isn't the first, (heavy) amplifier that he has shipped, so I have faith.:yes:
 
You're scaring me.:sigh: I Just got the tracking #, my amp will be here on the 14th. Man I hope it is in good shape. I have had good luck so far, my 40 plus pound KA-801 got here all the way from Washington State in good shape (and we all know how fragile the switches are on them), the Yamaha is coming from Texas. I have talked to the seller and this isn't the first, (heavy) amplifier that he has shipped, so I have faith.:yes:

The M-4 had been worked on before and the bonehead (not necessarily assuming the seller) left out the lower support for the main PCB (with heavy caps) and the top cover/bolt. A sure recipe for damage. A good, solid amp can survive some pretty rough handling with enough bubble wrap and a solid box. I received a CR-1020 that was stuffed into a too small box and double boxed in yet another too small box with less than 1" padding and it luckily made the trip OK.
 
My M-4 was purchased from eBay, and shipped across country in minimal packing. Amazingly in arrived with no damage. The auction stated it had a buzzing in one channel, so I was able to get it for under $60. It had a bad cap in the power supply, and after paying for the repair, it ended up costing me considerably less than they are now selling for.:banana: I'm hoping to come across an M-2 in similar fashion, but until that happens, I'm thrilled with the sound of my M-4.
 
My M-4 was purchased from eBay, and shipped across country in minimal packing. Amazingly in arrived with no damage. The auction stated it had a buzzing in one channel, so I was able to get it for under $60. It had a bad cap in the power supply, and after paying for the repair, it ended up costing me considerably less than they are now selling for.:banana: I'm hoping to come across an M-2 in similar fashion, but until that happens, I'm thrilled with the sound of my M-4.
Got a M-45 amp under the same circumstance. $30+SH plus $60 for 2 OEM capacitors from Yamaha.
 
I paid $84 plus shipping for mine. Even if I have to replace the pots, I don't think I did too bad.
 
I picked up my M-4 from a local pawn, one which I now boycott because they use eBay to establish their pricing yet there's always some major issue with the gear. The Yamaha is my one happy story, and I currently have it running a pair of Bozak 305's. Pure joy! I hope you enjoy yours as much as I do mine. $100, and I practically ran out of the shop.
 
Turning the ugly duckling into a swan

Well, I got it earlier this afternoon. It got here in good condition. It was packed with foam, but only 1/2 of it. It did suffer some minor damage, though I am not sure if it happened in shipping or not. The power cord was damaged where it enters the amp. I cut the cord, unsoldered it from the terminals inside and reattached it minus about 3 inches. The ground terminal is broke off in the back, but I guess I won't need it right now. Dirtier than hell inside, I don't think the top had ever been off, the screws were all "virgin". I blew the dust and spiderwebs out of it. The cage was badly scratched, I sanded it and repainted with some satin black paint.

All of the bulbs are out, no surprise there. Radio Shack, of all places, had them in stock. New bulbs are in. DC offset is fluctuating around 0 after being on for a few minutes. I had to adjust the left channel, it was around -60mv, tapering down to -30mv. I am impressed that it has no electrical problems. I will check the bias as soon as I find out how. I cleaned the pots and they are now quiet.

Other then some faceplate scratches that I have to address, this amp is in very good shape. As soon as the newly painted cage is ready to go back on, it is going in the system.

I have taken pics and will add them later, as my camera is out in the workshop with the amp. I know, I know. This thread is worthless without them.:yes:




I do have a question though. There is a switch on the back by the inputs labeled "AC-DC". What position should this be in for "normal", stereo use?

I know that question is open for jokes, but I am serious.:yes:
 
There is a switch on the back by the inputs labeled "AC-DC". What position should this be in for "normal", stereo use?
AC is capacitor coupled/ DC is direct coupled. Direct coupled:thmbsp:
 
Something's amiss. The left channel works fine, the right channel doesn't. I have not hooked a speaker to the right channel yet. I have some junk speakers I will use for finding out what, if anything, is coming from the right output. I get no output reading on the meter and the overload light comes on when it is fed a signal. I have a feeling something got jarred in shipping. I guess I will start pulling boards and checking solder joints. Is there anything I need to pay particular attention to?
 
Here's some pictures. Before cleanup and some minor repairs.
 

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Here's some after repainting the top cage, repairing the cord, and a general cleaning of the interior. Looks like I will be diving back in to find out why the right channel is not working. Since I will probably wind up pulling out boards, I will be able to do a more detailed cleaning too.
 

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I've got 0 bias. There is a small 1/4 watt resistor that is burned on the output board. Looks like I may have a bias circuit or voltage regulation(?)problem. There is -+ 65volts at the test terminals on the pre driver board. I won't be able to do much more until I get the service manual. I do like the way this amp is laid out. Modular construction makes it easy to work on.

I took a couple of pics of the burned resistor and of the board, zooming out.
 

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