Marantz 2245 - Right Channel - R763 not adjusting mV for idle-current

[Magnus Back]

Getting ready to go through the whole board. Can anyone tell me why there are caps between J758 - J753 and J761-JJ758 (0.1uF) and there is one on the underside of the board by H758 (c) and H758(b)? Are they necessary?

If I read the diagram correctly J758 is GND, J753 is 37V and J761 is -37V.
I don't see any 0.1uF in between in the circuit diagram.
Do you have a photo?

 

[Paul Malloy]

Both boards are the same. Looks to be factory. The ones on the jumper pins are 0.01 uF and the one on the backside at H758 is 500K (not sure what the unit it's in? Has a "yp" printed above the "500K", maybe pF?)

 

[Paul Malloy]

It is a chore to repair them, but I have done so just because subs just don’t work the same. I documented a repair here:
https://audiokarma.org/forums/index.php?threads/salvage-of-an-sv03-diode-from-a-2230.909528/

Steven-

I looked through your thread and these are the diodes that was on the board. I repaired the one that did still had one wire intact. It looks like you used silicone to seal the ends. I was thinking of encasing the ends in JB Weld to keep the wire ridged at the solder joint.

Again, the diodes are different, but not sure if it's just a different case or if one may have been replaced at one time. The one I repaired reads 637 mV, 31 pF. I couldn't test the other one (nothing I can connect to yet).

Paul

 

[bktheking]

Going back to an old thread, i broke one of these in a 2270 and used a 1n4007 as a replacement. Tom had the same findings. as a test. IIRC I covered it with shrink tube and covered it with thermal to help with the heat sensing.

Using my Fluke meter in the diode test position, which I believe feeds a 1mA current through the diode, an original 2270 Bias diode (SM-150-01) has a forward biased voltage drop of 0.558V and a new, unused On-Semi 1N4001 has a forward biased voltage drop of 0.557V. I don't see why a 1N4001 wouldn't work in place of the SM-150-01.

 

[bktheking]

Most of the time a zero bias condition will be a bad soldering job on a replaced component , an open resistor or a transistor that was installed with the incorrect pinout.

 

[Steven Tate]

Steven-

I looked through your thread and these are the diodes that was on the board. I repaired the one that did still had one wire intact. It looks like you used silicone to seal the ends. I was thinking of encasing the ends in JB Weld to keep the wire ridged at the solder joint.

Again, the diodes are different, but not sure if it's just a different case or if one may have been replaced at one time. The one I repaired reads 637 mV, 31 pF. I couldn't test the other one (nothing I can connect to yet).

Paul

View attachment 2138652

I used JB Weld on mine. That’s the grey material you see at each end of the diode.

 

[Paul Malloy]

Going back to an old thread, i broke one of these in a 2270 and used a 1n4007 as a replacement. Tom had the same findings. as a test. IIRC I covered it with shrink tube and covered it with thermal to help with the head sensing.

Using my Fluke meter in the diode test position, which I believe feeds a 1mA current through the diode, an original 2270 Bias diode (SM-150-01) has a forward biased voltage drop of 0.558V and a new, unused On-Semi 1N4001 has a forward biased voltage drop of 0.557V. I don't see why a 1N4001 wouldn't work in place of the SM-150-01.

Did you mount it to the heat sink like the original SM-150-01 was mounted or is it just on the board at that position like:

 

[Paul Malloy]

I used JB Weld on mine. That’s the grey material you see at each end of the diode.

Thanks-

 

[Paul Malloy]

Most of the time a zero bias condition will be a bad soldering job on a replaced component , an open resistor or a transistor that was installed with the incorrect pinout.

I did check the transistor pinout orientation and reflowed the whole board. Checked each solder joint for bridging.

 

[bktheking]

I mounted it to the heatsink, it had to go there as it's there to track heat changes of the heatsink.

 

[Paul Malloy]

I mounted it to the heatsink, it had to go there as it's there to track heat changes of the heatsink.

That's what I thought. So, you heat shrinked the exposed leads, and applied therma past to the diode body and had the body of the diode touching the heatsink.

That's how I did it when I replaced H760/761:



Thanks-Paul