Yamaha cr220 power supply help

usamike10

New Member
One day I turned on the system and audio slowly went down to nothing within 5 seconds.
I downloaded the schematic, did some checking and found that the -24vdc bleeds down as the +24vdc bleeds up. This all happens within 5 seconds of powering on.
I’m measuring on the filter caps c805 and c806.
I’ve opened the +/- 24 directly after the caps removing the load.
I’ve swapped the two filter caps with each other, tested the diodes supplying the +/- 24, and opened the 4 small ceramic caps that are in parallel with the bridge diodes.
Measuring on the filter caps now I have a stable -24 but the +24 climbs to upper +40’s before I power it down.
By opening the load for the +/- 24, is it normal to see the + side climb, seems odd? I’m running out of ideas for troubleshooting.
 
check d805 d806 c807
also clean fuse holders and check grounds .
but first check AC voltages to bridge rectifier .
 
AC feeding the bridge is 37vac, 18vac on each side when referenced from the transformer mid point 'E', so that looks good. d805 and d806 check good, removed c807.

I went ahead and replaced both filter caps with some lower voltage 47000uf caps I had just in case, but the problem remains.

Where would you suggest checking the grounds?
 
I replaced the bridge diodes and still have the problem. The scenario is this:
With +/- 24 load open (J104 and J105 open), the -24 is stable but the +24 climbs into the +40's.
With +/- 24 load connected, the -24 drops as the +24 climbs.
I also lifted the jumper J130 which feeds the 'E' midpoint 0v of the transformer to some of the other circuitry.

What is causing C805 to charge up past +24vdc? Or is it being caused by opening jumpers J104 and J105? Even with the jumpers in place it charges up but when the jumpers are in C806 also bleeds down.
 
I didn't with a meter, just looked at them and saw the filaments were in tact. But in fact F804 was open when checked with a meter!!

Now to solder everything back in place and see what happens, damn.
 
Tighten all ground screws between the pc board and that center steel rail. Most CR220s blew up because the screws did not maintain ground. If your iron is heavy enough you can solder jumper wires in parallel with the screws.
 
Okay Pete, you're good! All is good now, it was just a simple open F804 going back to the center of the transformer.

It's not the first time i've missed the simple cause in search for a more complicated approach!!

Nakdoc, I'll take your advice on the grounds, thanks!
 
Yes, 4700uf.

I put original 50v caps back in, just used the 35v caps for troubleshooting. Thanks again for the help.
 
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