Yamaha CR 2020 41Vdc on outputs!

Mid-Fi

Super Member
This unit wouldn't come out of protection and I found big DC on R1 & L1. So looking into the service bulletins and inspecting the PS board sure enough, all the usual suspects. I ordered parts and swapped the resistors and caps and reflowed the joints and still...41Vdc on R1 & L1.

This unit shows ~ +/- 59Vdc B+ and ~ 110Vdc b- which the manual shows to be pretty much spot on.

I am no tech so this is as far as I know to go. Any help is appreciated. Thanks, Victor
 
Seperate the pre-amp from the power amplifiers with the coupler switch on the rear panel. Then recheck your DC offset on R1/L1.
 
Sounds like a power supply issue if its both channels.
 
If you burnt the voice coil in a speaker...
1. Someone has jumpered over the protect relay.
2. Or..Your protect relay is welded.
3.Or.. the relay driver transistor is shorted.
 
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While avionic is getting a couple of hours sleep.

First step is to identify problematic channel. LI and RI are
connected by 2x47k resistors so a dc offset on one will kinda
appear on the other. Important to know the sign of the dc offset,
looks like positive 41Vdc. Please confirm.

Measure dc voltage between RI(RED probe) and LI(BLACK probe), probably
need mV scale, important to note sign pos or neg mV.

positive xxmV indicates problem on right channel (yellow wire)
Negative xxmV points to left channel.

Man, you should be sleeping...
 
I don't have a good way of finding faulty TR, just slow voltage measurement, alternatively need to start
testing transistors, start with TR611???
 
Check your solder connections on regulator pass transistors TR712 & TR715
 
take a look at R741, 2. They connect RI and LI
To the protect circuit ? I suppose if they were both "open" that would disable the protect circuit and the relay would always "set".
 
I suspect a power supply issue for the 41 volts of offset on both R and L channel.
 
The burnt speaker is a secondary " protect circuit " issue.
 
Great, I'll check all the above as time permits but keep the thoughts coming.

To clarify, I fried the speaker because I did something stoopid by attaching the speaker leads to L1. :confused: At least I learned to test outputs for DC if the relay doesn't close. :whip:
 
90% of the time, such high dc is caused by a failed component in the power amp stage.
What's slightly confusing is both channels have same dc, this is explained since RI
and LI are connected in the protection circuit via R741 and R742.

First step, identify faulty channel by measuring voltages between RI and LI as per
post 9.

Once faulty channel identified you have a choice of a labourous hunt to track down
the source of this voltage via voltage measurement or you can diode test key transistors.
In circuit diode test will probably be ok, looking for a short. In this case I suggest
diode testing starting with TR611, TR612
 
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