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Overprotective Yamaha CR-820

R

rauridh

New Member
Hi. I picked up a Yamaha CR-820 a month ago and thought I had fixed it three weeks ago but...nope.


When I got it, I had power, no relay click.
Read some threads here, downloaded schematic, parts list and service manual
Replaced capacitors on main power board, output transistors and built up some solder around the plate where the board grounds to via 4 screws.
Turned it on and heard the click. Adjusted the bias took it into the living room and enjoyed it for about 5 days.
The 12v lamps were burnt out so I decided to replace them, with 12v lamps. Turned it on and no click.
Removed lamps and wires for lamps from the main board. Turned it on, no click and R702 popped.
Noticed I mistakenly put a polarized cap for C752, corrected mistake.
Replaced R702, R764, D712, TR720, TR721, TR722, TR719.
Removed and tested output transistors, all good.
Turned it on and no click.
This is where I am now:

No relay click, TR720 gets really, really hot. No DC voltage on TP1 to TP2 or TP3 to TP4. No voltage on gold coils. Lamps are still disconnected.

Any suggestions on what I should do next would really be appreciated. I am currently giving it dirty looks when I pass it and I am usually not that way. It is a nice looking unit and the sound was great for the five days it made any.
 

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Or was it FR702 ? 68Ω 1/2 watt ? (68Ω @ 85ma)
 
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Thanks for responding avionic. It was FR702. 68Ω @ 85ma and I just noticed I replaced it with 68Ω @ 1/4 watt. Could this be the issue?
 
Looked over things, found that I replaced FR702 with a 2ohm resistor (mouser sent me two different value resistors in one bag). I replaced it with a 68ohm 1/2 watt. TR720 now gets just as hot, just faster. Any suggestions from anyone that knows anything would be welcome. Thanks.
 
Check D712 out of circuit. Have you tried to check/adjust the bias on the left channel?
 
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rauridh said:
Could this be the issue?
Click to expand...
These are fusible resistors. Putting a 1/4 watt where a 1/2 watt belongs is like putting a 5 amp fuse where a 10 amp belongs. If it was and issue the 1/4 watt would have smoked by now.
 
Any who.. First you need to verify that your regulated and unregulated DC power supplies are all working. And getting to there proper destinations.
 
Check all the fuses for continuity with your multimeter . Might want to also check FR801 in the PS.
If FR801 is bad it is and 1/2 watt as well @ 22 Ω
 
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TR720 (MJE15030G) tested against new out of circuit, same values as new transistor. I did the same for D712 (1N418), same value as new diode and C752 has a new 1uf 50v bipolar capacitor.
 
FR801 is fine. Pulled pads when removing TR720, ugh. I will check bias when I get TR720 to stay put. Thanks again for your help avionic.
 
The OP hasn't been active in over 4 years. Don't hold your breath.. :biggrin:
 
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