RCA RT2770 Reciever (Home Theater?) Need help!

[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.

[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

[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!

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!

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.

[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...

[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!!

[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?

[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!

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

[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!

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.

[budm]

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

[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.

Oh and I forgot to mention I live in bahamas and the U.S, though I still am from Guernsey, Channel Islands, U.K

sry for the confusion

[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.

I don't know all these formulas. :S I am a n00b.

Bur, I can tell you that I drive my speakers quite strongly usually, so wouldn't (for the sake of the amp) a high resistance be appropriete?

I was already getting some static noise from the speakers evan on volume level 1 without the sub (I can't get that sub working as I don't have the switch/button to complete the relay circuit thing that is reffered to as "subwoofer control" (that's another story)

Ah... progress... how I hate thee .

Anyway, back to the topic at hand: I guess the stattic was due to the bad resistor (well, it probably is, I mean, It's color coding rings where burnt off,
almost like how the sun bleaches a dead starfish). The capacitor that completes the snubber probably suffered due to burns present on the epoxy close to the end of one of it's leads, most likely caused by resistor leaning on it.

Lol, sorry I talk so much. I'm just a very inquisitive person ^_^.

I already have 2 (sligthy different) RCA RT 2770's so i may as well revamp one of them.

Plz give your honest opinions about each of the ideas I descibed.

I'm not trying to be a pain in the ... but I do like to understand how things work, for mental and physical benifits. I don't wanna set any boards up in flames.

[tom66]

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.

[Wolf_Punch]

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

I may be a novice but I no what a snubber is.

Anyway I have a whopper 8.2 Ohm resistor on my other RT 2770 (bare in mind it's got a different lay out ). Would that work in place of the burnt one of the other board?

It in the same basic area that the burnt resistor on the other board is right by the 3-pin heat sink mounted diode.

OH, and fyi, my board still works (Well probably not now since the resistor wiggled free of it's soldered terminal) but that slightly burnt resistor haunt's me .

I'm also thinking about upgrading all the 63v 1000uF caps for 100v 1000uF caps (Extra 27 volts of overvoltage cushioning ) along with the 2, 200v 330uF caps, to 250v 330uF caps. I blast my systems constantly, when they work, lol

[tom66]

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

The resistor is a snubber for the diode. Due to poor design, the wrong value has been chosen, which has led to early failure. Increasing the value should be harmless.

[Wolf_Punch]

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

BudM I hope these will do for pics. I dunno how you would prefer offsite photos or on site so I figured I'd post them on site.

Dude, that's like the same resistor that is burnt on mine, though mine still works, oddly.

I can't tell the bands on it eighther because it burnt a little too.

Oh, and another thing? How do I get this stupid subwoofer output to switch on?
I don't have the stupid sub control button and the relay that controls it is switched off

why, oh, why?

[budm]

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

Lol.