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Discussion Starter · #1 · (Edited)
All,

I have RCA RT2770 and have diagnosed the problem.

R202 along with C211 make up the "snubber network" for the fast action diode pack (TO5 Tab mounted on 2nd large heatsink) labeled D207. This resister is so burnt, on my unit, the color bands are not readable, so the value can not be determined. Obviously, by size, this is a 1 watt resistor. This resistor goes out when C211 shorts out at high voltages. Normal testing will not show the short, since it is an arching short at high voltage. On my system C211 has no markings so I need this value also.

From my knowledge of High Efficiency Switching Power Supplies, they use high frequency switching (pulse width modulation is used to vary signal width to increase amperage under load). Snubber networks are needed to chop off the high voltage spikes that occur. These spikes vary as the input voltage varies. Typical voltage here in the US varies from 105 to 125 VAC. Therefore the spike voltages at the upper end can easily exceed 30 KVAC.

Since I used to repair switching power supplies, the design engineers typically under rate the capacitor at 10-25 KVAC, which should be 35-50 KVAC. So when you replace this capacitor, get one with same capacitance rating (critical for resonance with the frequency of the design) but add 10-20 KVAC to the voltage rating from the schematic (35-50 KVAC).

I'm trying to find the value of these 2 components, so please share if you have this knowledge.

This power supply is used in many similar surround sound and audio amp system by RCA, so this solution will be good for other models also.

Failure of the snubber network is the most common failure in switching power supplies, so hope this is added to a FAQ section, if it exists here on this forum.

Cheers!

OMR
 

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For burned resistors, you can estimate the value pretty closely if you gently scrape back the surface to the conductor and find the open segment. You can then measure from there to each end and add the resistance. You have to be very careful, but larger resistors are often wire wound and pretty easy to do this with.
 

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Discussion Starter · #3 ·
For burned resistors, you can estimate the value pretty closely if you gently scrape back the surface to the conductor and find the open segment. You can then measure from there to each end and add the resistance. You have to be very careful, but larger resistors are often wire wound and pretty easy to do this with.
LC,

Is film type resister and burnt to bad to attempt any such thing. Need someone with actual schematic on this. Reached out via email to RCA, but no response yet.

Will submit values when I find them as I see lots of posts on this here on this board!

Cheers!

OMR
 

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Discussion Starter · #4 · (Edited)
All,

OK RCA, sent me email, but no values yet. Replied and gave tech there the breakdown on this. Hope I get answer with values soon!

Per write up, see Bad Caps links previously entered, some models have this resister valued at 8.5 ohms 5Watts, but as I said earlier, must replace C211 also as it is shorting so takes out R202.

Cheers!

OMR
 

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Hello, I have the same problem, except I'm changing the resistance and r202 and C211 condansator. settle the problem was and after some time the system has its start and turn close to nothing, like when I listen to a movie for example.
 

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@OldManRiver, I'm not sure if RCA will give you values of their components like that, it's mostly their business policies that stop them from giving such information. If you have some soldering skills, you can just take the capacitor out of the board and measure it yourself, that's the easiest way around this problem. And you're quite right about using the capacitor of higher rating, people generally don’t care about these things but one gets so much more reliability out of so less additional cost. Anyways, do let us know how you managed to solve this issue.

low volume pcb assembly
 

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did anyone ever find the R202 size for RT2770? I have one RCA RT2770 that works and one that does not work. Both have the R202 resistor burned such that it can not be read. Both have the March 23, 2007 manufacture date. Thank you
 
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