RV-NB50 - Front panel no power

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Mehmet

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From the fact that the CD also doesn't spin up, I recon that there is some issue in the 5V VCC between the power supply and the MCU circuit, since the amplifier and tuner use 15V.
 
hopey

hopey

Member (SA)
It maybe a chip going to ground. You could try to clean all PCB's and power up with the boards floating. Good luck.
 
Wes125

Wes125

Member (SA)
i dont like those touch power buttons. its another thing to go wrong. i had a jvc video recorder what kept turning its self off after 15 minutes..i turned out to be a little strike up capacitor. 1uf 50v. i replaced it with a 2.2uf 63v one and never had a problem with it ever again
 
Wes125

Wes125

Member (SA)
the trouble with this modern stuff the heatsinks get scalding hot and some of the microchips do aswell. then the solder joints dry out and break down. thats when you start getting problems like you've got. check the circuit boards for heat damage and dry solder joints
 
M

Mehmet

New Member
Preliminary research showed this:
It is actually a 3.3V circuit, and as far as I can see, the problem should indeed be with the 0.22F 5.5V supercapacitor. After opening it up:
IMG_0185.JPG
The confirmation. Well, I cleaned it up and replaced the .22 supercapacitor:
IMG_0188.JPG
IMG_0189.JPG
For the record, the accident waiting to happen was a Starcap, manufactured by Korchip, a subsidary of Samsung. The replacement is branded Eaton (which seems to be a rebranded Panasonic EECS0HD224H), according to whose website...
Eaton's KR family of supercapacitors replace button cell batteries (and the battery holder) for real-time clock backup power, and provide ridethrough for battery operated devices to allow time for battery replacements. The KR has excellent life time in typical 3.6 V systems. The family is RoHS compliant.
Click to expand...
...it can be replaced with a CR2032 battery, which certainly would prevent this from happening again ~10 years from now.

But I digress. After replacing the supercapacitor it showed 3.3V at one end, yet the unit still wouldn't turn on. I'm going to replace the 4+3+3 resistors and the diode next, and see what happens.
 
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hopey

hopey

Member (SA)
If the IC is down to ground that would put a dead short on that battery and the supply to it.
 
M

Mehmet

New Member
R279 - Connects 15V to Q301 Mosfet (OK, since the supercap measures 3V)
D318 - Connects 3V to the supercapacitor (OK, since the supercap measures 3V)

R305 - Connects to the CD door switch (OK, but it didn't spin up)
C322 - Connects to the CD door switch (OK, but it didn't spin up)

R390 - Ground

R382 - Connects to the power LED and CD door switch
D315 - Connects to the power LED

D317 - Power supply to all things front panel related (which was indeed broken)
Click to expand...

From further study of the PCB diagrams I conclude that the only explanation which makes sense here are the D317 and D318 schottky diodes.

Also the service manual is faulty, as it lists the resistors as 100k and 37k where it should be 10k and 47k. And for the sake of argument I ordered the CR1225 (again, not CR2032) battery and holder, which should work just fine since D318 drops 0.7V.
 
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