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Yamaha CR-820 - guidance and possible help needed

Hi!
So I re-measured the D812 and D813 with my analog multimeter. From what I can see they measure ok, so I resoldered them back into the circuit.

With the amplifier fuses (F801, 802) pulled, I went a head and fired up the unit with no luck. The DBT still lits up like before and I only get a few volts (around 3-4V) between the secondary outputs (re-red)

Could it be that the diods test ok out of circuit, but when soldered in, they short out? The diods where soldered in place the same way that they were fitted before I took them out. The SS-3R sits closest to the filter caps. See added picture.

Update: So I desoldered the diods again and then the voltage returns to the prevoius measrued level (67V-ish) (between red-red). Seems that the doids somehow shorts out the circuit. I also measured the voltage over the filter caps (with diods in circuit) and I only have 2.7V and -2.7V respectively.
 

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With an analog multimeter. One test lead to the metal arch and the other to the pin.

SS-3 - Red test lead to metal arch, black test lead on pin on diod for continuity.

SS3R - Black test lead to metal arch, red test lead to pin for continuity.

Reversing the test leads on both gives no continuity.

Hope this makes any sense.
 
JorgenSWE said:
With an analog multimeter. One test lead to the metal arch and the other to the pin.

SS-3 - Red test lead to metal arch, black test lead on pin on diod for continuity.

SS3R - Black test lead to metal arch, red test lead to pin for continuity.

Reversing the test leads on both gives no continuity.

Hope this makes any sense.
Click to expand...
:thumbsup:
 
Measure the continuity between the output transistor cases ( collector) and metal chassis ground..
 
Well, decided to review some of my previous work. :) When measuring between chassie and collector when all screws are in place, gives full continuity on all four, collector to chassie ground. But when all screws are out, only held in place by the paste, I get continuity only on the 4G (second and last seen from front to back)

I mounted them with new mica insulators and new paste. Made sure they seated correct in the socket. Screwed them gently to the chassie. Am I missing something here?

Hmmmm... Just relized that there are no nylon washers between the chassie and the collector to isolate the screws (ie chassie ground) from the collector. The odd thong is that there were no washers there in the first place.
 
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Check that the transistors are not mounted 180° out. ie. upside down .. This would allow the screws to contact the heatsink.
 
Looked to see if I had any washers, found only four. So I will have to order those.

Yes, this is defenitley what is causing the problem and shorting the rails to ground. It was a solid short, since the DBT lit up like it did.

How could the unit eve have funcioned earlier when this was such a major fault. Well I guess we will nevwr know.

Report back when washers are mounted.

The
 
avionic said:
Check that the transistors are not mounted 180° out. ie. upside down .. This would allow the screws to contact the heatsink.
Click to expand...
Ok, well since the e,b is not centered on the chassie, can they be mounted in any other way? It will not fit the holes for the screws. But I will check!!

Now they are mounted "upside down" looking from the side. Text is upside down.
 
A solder bridge on the circuit board is also a possibility... Shorting out the sockets collector pin connection.
 
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