RCA RT2770 Reciever (Home Theater?) Need help!

[Wolf_Punch]

Re: RCA RT2770 Reciever (Home Theater?) Need help!

There is a small value cap which is in series with the resistor to create RC Snubber circuit to reduce the Diode switching noise, if that cap is shorted or it has low leakage resistance, the resistor will burn up since the current will also flow through the resistor for full cycle.
example:
https://www.badcaps.net/forum/attach...9&d=1354513907

So it not the fact the diode it a puny, underated component? because this has happened to alot of ppl that have this model.

[Home_Command_Center]

Re: RCA RT2770 Reciever (Home Theater?) Need help!

the 3 leg transistor did not fail in my case, when I removed the resistor, nullifying the snubber circuit, the thing powered up and didnt really make a lot of hiss without it.

as for the sub switch, it's a little two pin connector you see for fans in PC's. just cut the lead off an old PC fan with the correct connector, plug it into the back, and use the two wires to complete the circuit. then your sub channel will work.

I caution you though, check the ohm load of your sub first, it needs to be 8ohm or greater, as when I had a 4ohm sub attached, the IC for the center channel and sub turned to toast, and that is what killed the resistor/snubber circuit. I've searched the earth for a good audio impedance matching transformer for this application and not found anything that will work for a subwoofer at a cost reasonable for use with a HTIB. your best bet if your sub is below 8ohms is to find a cheap home mono-block amp for the sub and run it from the RCA subwoofer output.

[Wolf_Punch]

Re: RCA RT2770 Reciever (Home Theater?) Need help!

Oh, and another question, did this happen to anyone else?

There are some chips on my other RT 2770 (a 2009 model, well, at least the power board seem to be) in the dolby section and I believe they are voltage regulators, might that be another one of the causes of poor dynamics in the music being outputed? The chips have burn marks on the top of the pcb but not in it, maybe the resin from the solder on the tiny little heat sink caught but I can't tell if the chip is fried a half of it is buried under that tiny tab of stainless steal thats supposed to be a heat sink. |:[

unfortunately I don't know the ratings of it and doubt id be able to read it as it probably burned off the white marking that denote what type of regulator it is.

There are three of these little pests and I don't think all of them are regulators, but at least one or two of them are.

I'm pretty much a n00b so plz help me understand :S

[Wolf_Punch]

Re: RCA RT2770 Reciever (Home Theater?) Need help!

I caution you though, check the ohm load of your sub first, it needs to be 8ohm or greater, as when I had a 4ohm sub attached, the IC for the center channel and sub turned to toast, and that is what killed the resistor/snubber circuit. I've searched the earth for a good audio impedance matching transformer for this application and not found anything that will work for a subwoofer at a cost reasonable for use with a HTIB. your best bet if your sub is below 8ohms is to find a cheap home mono-block amp for the sub and run it from the RCA subwoofer output.

That perfectly fine I was using a 8 Ohm sub already with my old receiver (another Rt 2770 but a 2009 model).

Btw, did you happen to have any mildly burnt and possibly fried voltage regulators in the Dolby/Input section of the amp, because my old one (The 2009 one) is has that problem, I wonder if that mainly what's causing the minuscule grit and lack of dynamics along with the bulging caps here and there, more noticeably the one's on the Final stages of the amp?

[Wolf_Punch]

Re: RCA RT2770 Reciever (Home Theater?) Need help!

8.2 ohms is too low, much too low.
You need about 1~100kohm 3W.

Depends on the output voltage of that PSU and breakdown voltage of diode.

If output is 50V and breakdown is 200V, worst case is 250V across resistor.

So calculate (MaxVoltage^2)/Resistance <= 1.5W (half rating of 3W to limit dissipation)
and that will give you a decent lower bound... Example 47kohm works here.

Ooooooh.... *idea

would a wire wound resistor of that resistance be a good idea for it's more efficiant cooling, I could heatsink to the case, no?

[tom66]

Re: RCA RT2770 Reciever (Home Theater?) Need help!

A higher value should be fine. Just poor design has lead to the failure of the resistor. If you have to heatsink the resistor, you doing it wrong!!

[Home_Command_Center]

Re: RCA RT2770 Reciever (Home Theater?) Need help!

That perfectly fine I was using a 8 Ohm sub already with my old receiver (another Rt 2770 but a 2009 model).

Btw, did you happen to have any mildly burnt and possibly fried voltage regulators in the Dolby/Input section of the amp, because my old one (The 2009 one) is has that problem, I wonder if that mainly what's causing the minuscule grit and lack of dynamics along with the bulging caps here and there, more noticeably the one's on the Final stages of the amp?

not in my case. after removing the burnt ic for the center channel and sub amp part of the D-AMP board and taking the burnt resistor out of the snubber circuit it works perfectly fine on the remaining 4 channels. all the other features work and the RCA un-powered sub output is even controlled by the signal processing board.

if the filter caps on the output side of the D-AMP board (the rows of black ones between the row of ICs and the speaker terminals) are bloated then I would definitely pull the heatsink off the row of ICs and check to make sure they aren't overheating...

[Wolf_Punch]

Re: RCA RT2770 Reciever (Home Theater?) Need help!

not in my case. after removing the burnt ic for the center channel and sub amp part of the D-AMP board and taking the burnt resistor out of the snubber circuit it works perfectly fine on the remaining 4 channels. all the other features work and the RCA un-powered sub output is even controlled by the signal processing board.

if the filter caps on the output side of the D-AMP board (the rows of black ones between the row of ICs and the speaker terminals) are bloated then I would definitely pull the heatsink off the row of ICs and check to make sure they aren't overheating...

they are slightly bulged, hence the reason I'm thinking about replacing them with same capacitance electrolytics at a higher voltage (100v instead of 63v) and a higher max. operating temperature (105*C instead of 85*C). It may sound a bit over the top, but the added protection helps when blasting music .

So, anyway, you think I should just put new thermal grease on it? It sounds gritty when you start playing music without it being warm in the first place, hence the reason i might upgrade the caps on the amp's final stage.

Oh and the fan in gonna be replaced, but i think the damage may already have been done .

It still works, that's a good sign.

[budm]

Re: RCA RT2770 Reciever (Home Theater?) Need help!

If you want to improve reliability of that ClassD output filter network, you should change those lytics cap to poly film instead, it will be more expensive and larger. Manufacturers always skimp on using quality parts like this Infinity sub woofer.
http://s807.photobucket.com/albums/y...inity%20PS-10/

[Wolf_Punch]

Re: RCA RT2770 Reciever (Home Theater?) Need help!

If you want to improve reliability of that ClassD output filter network, you should change those lytics cap to poly film instead, it will be more expensive and larger. Manufacturers always skimp on using quality parts like this Infinity sub woofer.
http://s807.photobucket.com/albums/y...inity%20PS-10/

It's actually class B, well, at least it says it is.

But do they even do poly film caps at 1000uF? the highest i could find were in the single and double digit uF range. :S. and I'm not gonna build sloppy cap banks that'll have to be on there own bread boards.

Wait, R U talking about the Dolby section? because it is possible to replace some of the caps their that are 1uF or 2.2 uF. in that case yes. But the final stage amplifier electrolytics would be an absolute pain to replace with poly films.

[budm]

Re: RCA RT2770 Reciever (Home Theater?) Need help!

"RCA RT2770' uses Class D amp as you can see from the picture and the spec. No audio amp uses Class B, too much distortion, most uses Class AB amp, or more expensive one will use Class A. Where did you get that Class B info from? the Class B label on the back is for FCC Class B compliance because it uses switching power supply and switching amplifier.
Learn more here about Class D output filter network.
https://cdn.badcaps-static.com/pdfs/...974574fbd7.pdf

[tom66]

Re: RCA RT2770 Reciever (Home Theater?) Need help!

The only reason 1000uF filter caps are used is to get the ESR lower. You just need a 1000uF electrolytic plus a few 1~3.3uF poly caps.

[Wolf_Punch]

Re: RCA RT2770 Reciever (Home Theater?) Need help!

The only reason 1000uF filter caps are used is to get the ESR lower. You just need a 1000uF electrolytic plus a few 1~3.3uF poly caps.

So would it be wise to up the 63v electrolytic 1000uF caps to 100v caps, because the cheapo one's they used are bulging.

[Wolf_Punch]

Re: RCA RT2770 Reciever (Home Theater?) Need help!

The only reason 1000uF filter caps are used is to get the ESR lower. You just need a 1000uF electrolytic plus a few 1~3.3uF poly caps.

Oooh, does that mean I could change the crossover frequency of the sub channel by changing one of the poly films to a higher capacitance, or would that mess with the chip :/, because all the channel are copies of them selves so it probably wouldn't like diversity when it comes to its apperently symetrical channels. It also seems to look like it has a possibly bad input stage (it always freezing).

The 2007 model one I recently bought only has a pesky relay, which apparently, since it's a self powered relay circuit, just need a jumper across the two terminals for the switch to impermanently close the circuit.
Not pesky anymore ^_^

It also has some bulging lytics in the power section, that I might swap out for the good lytics on my 2009 with a higer temp rating with that pesky snubber resistor that burnt its self right up but still somehow works |:/.

Btw, anyone know anything about that snubber resistor: Can anyone recommend a wire wound replacement for that snubber resistor, I know one of you send something about a 47 kOhm resistor, but I think that was just for example purposes.

Also, btw, if I remember correctly, that snubber cap is a high voltage,blue epoxy coated, 2200pF 1KV ceramic capacitor. If I'm not correct on the ratings, then the marking (if you need correct me) are
222K 1KV, and another letter, but I don't think the other letter really means much, as a guess it's probably just to denote the size.

i know K denotes a certain tollerance, the first 2 numbers denotes the capacitance rating without the multiplier, which is the 3rd number. Everyone know what KV mean's though .

Can the snubber resistor resistance value be determined by the snubber cap value?

[budm]

Re: RCA RT2770 Reciever (Home Theater?) Need help!

Where are these 1000uf caps you are seeing, not in the Output filter network for the Class D amp for sure. The cross over circuit is done BEFORE the sub woofer power amp section.

[Wolf_Punch]

Re: RCA RT2770 Reciever (Home Theater?) Need help!

Where are these 1000uf caps you are seeing, not in the Output filter network for the Class D amp for sure. The cross over circuit is done BEFORE the sub woofer power amp section.

I kinda said it wrong.

I'm newb. :$

anyway, i don't really truely know what the hell it is, but there's lytics and poly films in the same general area of the amps output stage, like right before the inductors around the speaker terminals. The black (sometimes blue depending on models since i have two RT 2770's but different year models) are slightly bulged. The same is true for my other RT 2770. They have been bulged for a while, so I don't know why the receivers are giving me grief.

I think the 2007 model has a bad resistor (that I already removed) and the 2009 model has a bad votage regulator (there are brown markings on the little heat sink metal tab thing.

My guess is the 2007 model will be easy to fix, well as the 2009... well that'll be a challenge. Does anyone know the part numbers for the 3 SMD chips on the dolby/input board of the 2009 model. They have three leads so they're probably some small MOSFET or voltage regulator of some sort i guess.

[hardwareguy]

Re: RCA RT2770 Reciever (Home Theater?) Need help!

The 4 large lytics on the amp board are rail stiffening caps. DO NOT replace them with film. The small film caps present on the board are part of the output filtering network.

Mine has no audio....I think something is FUBAR on the DSP board.

[siski123]

Re: RCA RT2770 Reciever (Home Theater?) Need help!

the r202 is RESISTOR 8.2ohm +-5% 5W. confirmed for rca

[OldManRiver]

Re: RCA RT2770 Reciever (Home Theater?) Need help!

pics of my resistor:

HCC,

I'm not sure of the color bands I'm seeing here. Is it Brown, white, black, gold? Gold is the tolerance percent rating (5% for Gold) and always must be the 4th band, so what is it.

If it is Brown, white, black, gold then value is 190 ohms, which should be right for this "snubber network".

For more info on this ckt and snubber networks, see my thread at:

http://www.hometheatershack.com/foru...er-supply.html

Cheers!

OMR

[OldManRiver]

Re: RCA RT2770 Reciever (Home Theater?) Need help!

the r202 is RESISTOR 8.2ohm +-5% 5W. confirmed for rca

siski123,

My model PWR brd (MAR/23/2007) the resister is film type like pix shown and is a 1W resister. However it is not the resister that is the problem. It burns only when C211 shorts, under high voltage. Spikes on this exceed 30KVAC.

You have to replace the cap or resister will continue to burn out.

Cheers!

OMR