M-70 Needs Help

Ok so I'm starting my own thread that continues the discussion started on the recap thread for this same amp...

Here's where I'm at:

Picked up an M-70 that was in protection mode continually.

I recapped the power board (it had visibly leaking caps), C701 to C706 and the infamous .22mf 250v x2 cap (C607) on the control board. I also dismantled the relays and cleaned them.

It powered up and came out of protection which is good, but I'm not getting any sound (that I'm supposed to get)

Initially, it was making a high pitched hiss/squeal that went away after checking everything but I think it may have been a result of warming up. Because this morning when I started it up cold it had the same high pitched squeal. After 15 minutes of warming up with no signal applied and not touching a thing it slowly went away and is now non-existent. As the sound dissipated so did the meters from about 5 bars down to no bars. Might be from the relays because if I jack with them i can get remnants of the whine to come back. Not sure what's going on there but no sound coming from the source regardless.

Anybody know of a matching replacement to the DEC type MSJU 12vdc #531 speaker relays?

What's up with those magnets taped to the case on the side of the relays?

Here's what I've tested...

-B power supply voltage is at 69.1v
Photo coupler voltage is at 1.26v
DC offset at the speaker terminal with the relay off is -.7v left and 0.0v right

Any suggestions on how to proceed?

So after letting it set off for a couple hours to completely cool...I turned it back on and the whine is only there for about 30 seconds...maybe 20.

One thing I was wondering...I have the amp fairly disassembled is there anything in particular that needs to be grounded that would cut the sound otherwise? I have the power board grounding screw in and the longer screw that connects on the bottom of the capacitor board...are there any others that matter?

Obviously I want to get this guy working before I upgrade anymore parts...too much guessing otherwise.

These should fit
http://www.onlinecomponents.com/omron-industrial-my2-02-dc12.html?p=38193919

Yep I may replace those but I'm pretty confident these aren't the issue into no sound. I can visually see them working with the cover off and hear them
Properly clicking when they are covered.

My bottleneck is likely somewhere else.

Should I work my way back from the speaker terminals or forward from the source input?

DC offset at the speaker terminal with the relay off is -.7v left and 0.0v right

Click to expand...

Relay off ???

Do you mean set ( 1 click) or reset (no click)..You can't measure DC offset from the speaker posts if the relay hasn't "set".

.7volts---700mv way to frick'n high..

Actually my probes might not have been behaving...I may be getting somewhere.

When I take a measurement for dc offset from tpo+/tpe- with relay OFF I get 0.0 mV on both left and right. BUT, adjusting vr901 or vr902 has no affect on the reading

If I take the dc offset from the speaker terminals either through the post or from the back I get around -32.7 to -32.2 volts with the relay ON

Again these numbers don't adjust when vr901-902 are adjusted either

If I take the dc offset from the speaker terminals either through the post or from the back I get around -32.7 to -32.2 volts with the relay ON

Click to expand...

Shorted output or driver transistors perhaps.

Since both channels are behaving the same would that help point in the right direction?

Relay

avionic said:

These should fit
http://www.onlinecomponents.com/omron-industrial-my2-02-dc12.html?p=38193919

Click to expand...

Or this 653-MY2-DC12 relay with this 653-PY08-Y1 socket?

(mouser)

bhuskins said:

Since both channels are behaving the same would that help point in the right direction?

Click to expand...

Just to be on the safe side--Check from emitter to collector on TR134-150 for a shorted junction.

http://www.hifiengine.com/library/yamaha/m-70.shtml

I'll just add quickly that most Yamaha gear is notorious for doing weird shit if grounds are missing.

brutal said:

I'll just add quickly that most Yamaha gear is notorious for doing weird shit if grounds are missing.

Click to expand...

Thats a very good point!

If I take the dc offset from the speaker terminals either through the post or from the back I get around -32.7 to -32.2 volts with the relay ON

Click to expand...

But..

When I take a measurement for dc offset from tpo+/tpe- with relay OFF I get 0.0 mV on both left and right.

Click to expand...

WTF is going on here..weird!
Did you lift any solder pads when unsoldering stuff?
Is this unit still all semi-tore down ?

Another thought-- Did this unit look like someone else had tried to fix it?

OK...I'm back on this amp and I aim to get it up and going.

When going through the adjustment procedures

#1 -B Power Supply Voltage Adjustment - adjusts to 70.00v
#2 Photo Coupler Voltage Adjustment - adjusts to 1.200v
#3 DC Offset Adjustment - reads -36.1V for R and -36.6v for L and adjustments to VR902 and VR901 don't affect the reading
#4 Idle Current Adjustment - reads 0.00mv for R and 0.00mv for L

Obviously #3 and #4 are not correct...what should I check to get a game plan on what I need to tackle?

to review...
I fully recapped the power circuit board and replaced the C607 Oil Cap (X2) on the Control Circuit Board and that's about it. I also replaced a couple diodes and resistors that looked damaged from leaky electrolytic on the power circuit board...I tested all of the resistors on this board to confirm they were in spec. When I got the amp it was in protection and once I recapped it, it will come out of protection but shows the issues above.

HELP

No real signs of anyone else ever jacking with the amp...

Also, I tested TR134-TR150 and all test the same from
-E to +C around .75v to .85v with the diode test. This is with them in the circuit.

Anybody have any ideas on which direction I should go?

bhuskins said:

Also, I tested TR134-TR150 and all test the same from
-E to +C around .75v to .85v with the diode test. This is with them in the circuit.

Anybody have any ideas on which direction I should go?

Click to expand...

Pull them out of circuit and check the output and driver transistors.

Ahh...I figured you were gonna say that! Do these just have grease or do they have anything else I need to be careful with? Mica etc

bhuskins said:

Ahh...I figured you were gonna say that! Do these just have grease or do they have anything else I need to be careful with? Mica etc

Click to expand...

TR131 thru TR150 need to be checked for shorted condition. They will have either mica or Kapton strips and thermal compound between the transistors and the heatsink.
I believe you can just leave the transistors fastened to the heatsink and just unsolder and lift legs away from the circuit board - make your EBC checks yada,yada,yada..

Do a quicky check on them while in circuit -- emitter to collector. If you read anything less than 10kΩ on any of them pull it and recheck it .

These are all NPN right?