Need help with RCA rt2870 PSU

[ultimate360]

Hey guys, I have an rca rt2870 system here with a couple burned spots on the power supply PCB. (Photos will be attached)

It was just moved in a car and it didn't work when it was hooked up again. So I opened it up and right away noticed a couple black spots on the PSU. It looks as if one of the resistors near a MOSFET heatsink got knocked into it and shorted out and left a huge black area on PCB. I removed the resistor already, there is nothing left to see of it. I also noticed a slightly cooked looking diode as well which I included a photo of. Anyways, as you would assume, it doesn't power on, it clicks on then back off right away. I need some help to get this thing back to functioning order. I'll need to know what that resistor was first of all so I can replace it.

I'd really appreciate whatever help you guys can give me, thanks in advance!

[budm]

Re: Need help with RCA rt2870 PSU

That is an RC snubber network for that diode mounted on the heatsink. Did you verify if the diode is still OK?
the ceramic disc cap by the white connector in pix 3 is also broken.
So right now you are not getting and DC voltages from those three white connectors (they have label for each pin) at all?

[ultimate360]

Re: Need help with RCA rt2870 PSU

I haven't checked that mounted diode or the voltages on the cable connectors yet. I will look at those in about 2 hours. But visually, the diode looks fine

[budm]

Re: Need help with RCA rt2870 PSU

You should read this thread:
https://www.badcaps.net/forum/showth...ghlight=rt2870

[ultimate360]

Re: Need help with RCA rt2870 PSU

So from what I saw at that thread, that resistor isn't needed?

I'm not sure, he drifted off into another problem and started to ignore the resistor

[budm]

Re: Need help with RCA rt2870 PSU

The resistor-capacitor network for protection of the diode, for testing at this point you can leave it out since it will not stop the unit from functioning. You should remove the diode off the board and test it.
We still need to know what Voltages you are getting on those 3 connectors.

[ultimate360]

Re: Need help with RCA rt2870 PSU

Alright sorry for the wait budm, I have the info you wanted. First of all, here is the voltage test results on those 4 connectors off to the right, listed from top to bottom.

Plug 1:

fl+,fl- =.604
-26v = -5.09
5vs = 4.96
PC = (varies around -1)


Plug 2:

PD = 4.95
5v = 1.5


plug 3:

3v3 = .73
12v = 3.15
9vm = .76
-12v = -3.2
mond = -3.2


plug 4:

All 3 pvcc= 19.5




After I ran the voltage tests, I then isolated the diode from the circuit and tested that. It appears to be a PNP type. I believe it may be bad because I got a good test on one side (.4, then OL when flipped), but the other side is at 0 both ways, so I think that it's bad. (correct me if i'm wrong)

Anyways, hope this will help you spot the issues, thanks!

[budm]

Re: Need help with RCA rt2870 PSU

That diode is a dual diode with common Cathode in the middle pin, the two outer pins are the Anode.
So when the meter is in diode mode, black probe on middle pin, the red probe on each out side pin one at a time it should show as diode, and when you reverse the probe then it should show no conduction.
You are correct that it is NPN junction, so it does look like one of the 2 diode inside is bad.

[ultimate360]

Re: Need help with RCA rt2870 PSU

That diode is a dual diode with common Cathode in the middle pin, the two outer pins are the Anode.
So when the meter is in diode mode, black probe on middle pin, the red probe on each out side pin one at a time it should show as diode, and when you reverse the probe then it should show no conduction.
You are correct that it is NPN junction, so it does look like one of the 2 diode inside is bad.

Thanks for the info!

So i'll buy a new diode and get that installed probably tomorrow, along with the broken disk cap over by the pin connectors. Will this be enough to make this unit function?

[budm]

Re: Need help with RCA rt2870 PSU

That burnt out section of the board is the power supply for the power amplifier section and it is commanded to turned on by the processor for the logic board when the power switch or the power button on the remote is activated.
The other power supplies are for the logic board which is always running the minute the unit is plugged into the outlet.
The standby voltage 5VS is fine. The other readings do not look right. So you just have to replace the bad diode first.
BTW, the dual-diode is connected in parallel to form one diode as you can see the copper trace connects the two Anode together, it is a half-wave rectifier setup.

[ultimate360]

Re: Need help with RCA rt2870 PSU

Sorry for being so slow, I finally got around around to looking for that diode. Only one issue though, I have no idea what i'm looking for.. lol

What do I need to buy?

[ultimate360]

Re: Need help with RCA rt2870 PSU

Anyone know?

[Neelix]

Re: Need help with RCA rt2870 PSU

Can you see any numbers on the outside of the diode package?

[ultimate360]

Re: Need help with RCA rt2870 PSU

Can you see any numbers on the outside of the diode package?

Sorry for wait, yes I do:

HERI604CT


the "I" might actually be a 1, not sure

[ROGERIO RODRIGUES]

Re: Need help with RCA rt2870 PSU

Good morning,

Do you own the circuit diagram of the RCA RT2781BE? I need to service my device. or do you know where I can get it?

att, Rogerio..