CR-2040 power supply failure

Gregory

Soundco Kid
A Yamaha CR-2040 Receiver is now on my bench after an AK'er purchased it recently, and he asked me to take a look. The power supply for the lamp circuits is reportedly dead and blowing fuses, though power has not been applied and no fuses have been sacrificed yet to verify this. :cool:

I've been able to trace the problem (theoretically) thanks to the excellent factory Service Manual. Apparently D912 is connected to the power transformer center tap (25 VAC) YE (yellow) wire and is filtered by C927, a 470uF, 35V electrolytic. From there it feeds 8 panel lamps, and the dial pointer lamp through parallel resistors.

PS_schematic_09.jpg


A photo of the PCB with empty fuse holders.

D912_diode_05.jpg


Just so everything is perfectly clear, the schematic is marked-up below.

PS_schematic_01.jpg


I'm 80 - 90 % sure the problem is a blown diode D912, P/N W03B, also 1S1885.. 1A, 100 PIV silicon rectifier, commonly known in the USA as 1N4002?


Wanted to run that by some of you experts here.


Original thread: http://audiokarma.org/forums/index....p-when-turned-off-only-not-on-turn-on.493168/


-Greg
 
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This is the 'sister' receiver acquired along with the unit @Gregory is repairing - FM tuning is balky but once it settles on a station, all is good. I do have it connected to my garage antenna.

IMG_2828.JPG
 
5 each Paralleled .. 1KΩ 1/4 watt = 200Ω / 1.25 watt ;)

Of course, thanks for the correction. Obviously they're in parallel. :confused:


1) Could one of you gents comment on the best or appropriate replacement diode for D912? I'm thinking 1N4002.

2) What's the recommended lamp configuration for this Rx? One guys says "the correct lamps" (originals?) and others mention LEDs.


Below I have the dial lamp string pulled out. It doesn't look like stock wiring, though I have no Yamaha experience.

dial_lamps_LEDs_18.jpg


And the dial pointer lamp removed.

dial_pointer_lamp_17.jpg


Not to mention the lamp diffuser assy.

cover_lamp-bar_16.jpg


-Greg
 
What's the recommended lamp configuration for this Rx? One guys says "the correct lamps" (originals?) and others mention LEDs.
Flip a coin.Personally I prefer the OEM lamps. Your project. Your decision.:thumbsup:
 
Highly recommend dgwojo.com for your illumination needs.:thumbsup: Dave will hook you up.
 
I'm betting some one botched up the LED wiring and thats whats blowing your fuse.Or even possibly damaged the diode D912.
 
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I'm betting some one botched up the LED wiring and thats whats blowing your fuse.Or possibly damaged the diode D912.
If so.. Who knows what other " changes :rolleyes: " you may find on the lamp assembly circuit board.
 
Sacrifice a fuse. And power up with the LED's disconnected. If the fuse does't blow. Then measure your DC voltage out of the cathode end of the diode.
 
Sacrifice a fuse. And power up with the LED's disconnected. If the fuse doesn't blow. Then measure your DC voltage out of the cathode end of the diode.

Went ahead and powered it up with the Kill-A-Watt meter inline, and fuse F902 blew in ~3-sec. That was with four meter lamps (with original wire) CONNECTED, and four dial lamps & one dial pointer lamp DISCONNECTED.

The MAX wattage draw observed was 149W, and then it settled to 33-36W. I smelled something burning (or getting hot) but saw no smoke. Could not determine if any components were not to the touch.

Testing rectifier D912 in-circuit, it measured a virtual short in both directions. Time to replace the rectifier, or at least remove it from PCB and test again.


-Greg
 
Now the wrench in the works.. If using LED's with this lamp circuit power supply/ protect relay power supply. Yamaha depended on all the incandescent lamps to be functional to correctly operate the relay.Otherwise you would get power down "thumps" in the speakers. The LED's will need to do the same.
Hence if a lamp or two were burnt out you will get a thump.
 
Am about ready to pull that rectifier and order some parts.. you know, get the bench mat and tools out etc.

Was thinking about the LAMP situation – we used to call those originals "grain of wheat" bulbs back in the 70's. Here's the plan. Step 1: characterize how much current a single lamp draws. Step 2: determine a "dummy load" needed to operate five LEDs in place of the originals. The four meter lamps are still original.

-Greg
 
Greg, I am the guilty party who shorted the lamp circuit while working on a LED conversion like the one jbailey930 pictured above. After my short it immediately blows the fuses you see removed. I suspect something in the power supply circuits, but this was beyond my limited skills. As you can see from the LED upgraded 2040 that jbailey930 is running it is possible to swap bulbs for LEDs and not have a turn off pop. If you are missing any parts (bulb holders, screws etc.) let me know.
 
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