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Thread: Schematic for RCA RS2640

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    Schematic for RCA RS2640

    Does anyone happen to have a schematic for this all in one stereo ?? Was cutting out once it warmed up , now it just buzzes no audio .

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    Old Timer Leo_Gnardo's Avatar
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    Quote Originally Posted by shortcircuit View Post
    it just buzzes no audio .
    Classic symptom of a failed main filter capacitor. I don't have a schematic. It shouldn't take too much head-scratching to find that cap and clip another similarly rated one in its place, see if your prize starts working again.

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    Quote Originally Posted by Leo_Gnardo View Post
    Classic symptom of a failed main filter capacitor. I don't have a schematic. It shouldn't take too much head-scratching to find that cap and clip another similarly rated one in its place, see if your prize starts working again.
    Thank You , actually got one of them to spill it's guts , all my replacements are to low voltage ,will be on my next order.

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    Quote Originally Posted by shortcircuit View Post
    Thank You , actually got one of them to spill it's guts , all my replacements are to low voltage ,will be on my next order.
    Replaced both main filter caps plus one other, still just a buzz , you can hear the volume click up on the speakers, no audio output from any of the functions cd,tape etc or headphones. any suggestions ?? , start tracing
    100_2535.jpg
    Last edited by shortcircuit; 03-28-2018 at 07:00 PM.

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    Supporting Member The Dude's Avatar
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    Schematic is here:

    https://elektrotanya.com/rca_rs2640.pdf/download.html

    I would start by checking all power supply voltages.
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    Quote Originally Posted by The Dude View Post
    Schematic is here:

    https://elektrotanya.com/rca_rs2640.pdf/download.html

    I would start by checking all power supply voltages.
    Thank You very much , you are The Dude , appreciate your excellent support

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    Quote Originally Posted by The Dude View Post
    Schematic is here:

    https://elektrotanya.com/rca_rs2640.pdf/download.html

    I would start by checking all power supply voltages.
    rca-2-.jpeg
    D821= -31.47vdc
    D509-D512 =8.35vdc
    D505-D508 = 40.7vdc / -40.7vdc
    above and below 10% , bad transformer ??
    Last edited by shortcircuit; 03-30-2018 at 03:31 PM. Reason: +

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    Quote Originally Posted by The Dude View Post
    Schematic is here:

    https://elektrotanya.com/rca_rs2640.pdf/download.html

    I would start by checking all power supply voltages.
    rca-2-.jpeg
    D821= -31.47vdc
    D509-D512 =8.35vdc
    D505-D508 = 40.7vdc / -40.7vdc
    above and below 10% , bad transformer ?? not blowing fuses, I'm thinking I need to get voltages to IC501 the audio amp I don't have any

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    Supporting Member The Dude's Avatar
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    My apologies, I haven't gone through your measurements. A bit slammed at work today. If you don't have voltage to your audio amp, look at that rectifier circuit consisting of D505-D508. That's where supply comes from. Check the fuses F503 & F504. If one or both is open, it's likely one of your audio amps shorted. Check the audio amps supply pins to ground and to each other and make sure there are no shorts. If there are, you will just blow the fuses again. If those fuses are good, measure the AC voltage at N801A and make sure there is AC supplied to the rectifier circuit.
    “Yeah, well, you know, that’s just, like, your opinion, man.”

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    Quote Originally Posted by The Dude View Post
    My apologies, I haven't gone through your measurements. A bit slammed at work today. If you don't have voltage to your audio amp, look at that rectifier circuit consisting of D505-D508. That's where supply comes from. Check the fuses F503 & F504. If one or both is open, it's likely one of your audio amps shorted. Check the audio amps supply pins to ground and to each other and make sure there are no shorts. If there are, you will just blow the fuses again. If those fuses are good, measure the AC voltage at N801A and make sure there is AC supplied to the rectifier circuit.
    fuses are good, have 29.25vac at N801a , have 40.7vdc & -40.7vdc from D505-D508 , thanks for the reply , no apologies necessary ,appreciate all you do and have done
    ?? even if the amp was shorted wouldn't I have voltage to the pins 2&15 that should have 29.8v??
    Last edited by shortcircuit; 03-30-2018 at 11:24 PM. Reason: +

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    Supporting Member The Dude's Avatar
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    So you have DC out of the rectifier, but not at the IC suppy pins? If that's the case, you must have connection problems- cold solder, burnt trace, etc. Check continuity from your rectifier supply to the IC supply pins and verify that the connection is good.
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    The +/- 40V should be showing up at pins 7 and 8 of the amp IC's, they are not there? It should be a straight run from the rectifiers, no burnt traces?
    You said 8.35V at D510? What are voltages at pins 1&3 of IC503?
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    Old Timer J M Fahey's Avatar
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    As a side note, I wouldn´t worry about finding +/-41V rails instead of +/-31.

    TDA7293 are happy with both, 2 possibilities to explain the difference:
    1) a plain old typo. Happens in the best families. The writer might have wanted to say "31V **AC** ... which will give you about 41V DC rails.
    2) factory variation.
    Maybe original version used 31V rails, then they improved it and offered the higher ones, which increase power out.

    In any case, well within Power Amp ICs, so ...... no big deal.
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    Quote Originally Posted by g1 View Post
    The +/- 40V should be showing up at pins 7 and 8 of the amp IC's, they are not there? It should be a straight run from the rectifiers, no burnt traces?
    You said 8.35V at D510? What are voltages at pins 1&3 of IC503?
    Thank You g1
    Have +/-40vdc at pins 7 & 8 , I owe The Dude an apology on that , voltage at IC503 pin1 18.65vdc , pin3 11.76vdc ,
    IC501 pins 1,3,4,5,9,10,11,12 =0vdc pin 2=-1vdc , pin6 =13.35vdc (and starts dropping if you stay on it) 7&8 = 41/-41 vdc , pin13= 41vdc,pin 14= -1vdc , pin 15= -41vdc
    my mistake was was going off the voltage chart on pg7-1,which is no where close to any of these
    Last edited by shortcircuit; 03-31-2018 at 02:26 PM. Reason: +

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    Quote Originally Posted by J M Fahey View Post
    As a side note, I wouldn´t worry about finding +/-41V rails instead of +/-31.

    TDA7293 are happy with both, 2 possibilities to explain the difference:
    1) a plain old typo. Happens in the best families. The writer might have wanted to say "31V **AC** ... which will give you about 41V DC rails.
    2) factory variation.
    Maybe original version used 31V rails, then they improved it and offered the higher ones, which increase power out.

    In any case, well within Power Amp ICs, so ...... no big deal.
    Thanks for the intel , appreciate it

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    Supporting Member Jazz P Bass's Avatar
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    Pin #9 is the Standby pin.

    If it never raises above the zero volts that you measured, then the power amp ic is in standby.

    tda7293-datasheet-pinout.gif
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    Quote Originally Posted by Jazz P Bass View Post
    Pin #9 is the Standby pin.

    If it never raises above the zero volts that you measured, then the power amp ic is in standby.

    Click image for larger version. 

Name:	TDA7293-datasheet-pinout.gif 
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ID:	47921
    I get .064vdc on pin9 , with fm radio which is not 0vdc thank you, when this was working the fan only came on once you increased the volume , should this be running constantly?? It does run with direct 9v to it. I'm going to back track

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    Supporting Member Jazz P Bass's Avatar
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    Follow pin 9 (Standby) and pin 10 (Mute) on the schematic.

    Q501 (NPN transistor) is the active control element.

    rca_rs2640 Mute.pdf
    Last edited by Jazz P Bass; 04-01-2018 at 02:06 AM.

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    Quote Originally Posted by Jazz P Bass View Post
    Follow pin 9 (Standby) and pin 10 (Mute) on the schematic.

    Q50 9 (NPN transistor) is the active control element.

    rca_rs2640 Mute.pdf
    I think you meant Q501 ,this flea flea501.jpg
    testing in circuit DVM on diode mode, Blk to Base Red to Emitter .970 red to Collector 1.322 Red to base Blk to Emitter .699 Blk to collector .696
    Last edited by shortcircuit; 04-01-2018 at 12:53 AM. Reason: -

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    g1
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    How about D504 and D501?
    What kind of voltages do you get at E,B,&C of Q501 ?
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    Quote Originally Posted by g1 View Post
    How about D504 and D501?
    What kind of voltages do you get at E,B,&C of Q501 ?
    D504 cathode 11.75vdc anode 9.34vdc D501 cathode 5.22vdc anode 0vdc , Q501 E =0vdc B= .140vdc C= 5.22vdc

    in diode mode in circuit
    D504 + to C / - to A 1.163 - to C / + to A .700
    D501 + to C / - to A .683 - to C / + to A .654
    Last edited by shortcircuit; 04-01-2018 at 01:29 PM. Reason: +

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    Supporting Member Jazz P Bass's Avatar
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    "Q501 E =0vdc B= .140vdc C= 5.22vdc"

    So, if Q501 Collector is sitting at 5.22Vdc, why are the standby & mute pins (Pin 9 &10) at 0 volts?

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    Quote Originally Posted by Jazz P Bass View Post
    "Q501 E =0vdc B= .140vdc C= 5.22vdc"

    So, if Q501 Collector is sitting at 5.22Vdc, why are the standby & mute pins (Pin 9 &10) at 0 volts?
    Q501 is a problem child and not turning on

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    Supporting Member Jazz P Bass's Avatar
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    Quote Originally Posted by shortcircuit View Post
    Q501 is a problem child and not turning on
    Yeah but....

    Q501, if on, would pull the collector low and it is not low.
    It's at 5Vdc.

    So the question remains: 'why are pin 9 & 10 low?'

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    Quote Originally Posted by Jazz P Bass View Post
    Yeah but....

    Q501, if on, would pull the collector low and it is not low.
    It's at 5Vdc.

    So the question remains: 'why are pin 9 & 10 low?'
    this is humbling , had headphones plugged in . Now on IC 501 I have 5.20vdc on pin 9 and 5.15vdc on pin 10 , buzz, no audio
    Last edited by shortcircuit; 04-02-2018 at 12:56 AM. Reason: -

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    Old Timer J M Fahey's Avatar
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    Quote Originally Posted by Jazz P Bass View Post
    So the question remains: 'why are pin 9 & 10 low?'
    Thank you JPB.

    If you don´t mind, I´ll use that as the title of my next Movie.
    Regards
    Alfred.
    Juan Manuel Fahey

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    Quote Originally Posted by shortcircuit View Post
    this is humbling , had headphones plugged in . Now on IC 501 I have 5.20vdc on pin 9 and 5.15vdc on pin 10 , buzz, no audio
    Jazz P Bass(or any supporting member) are you still seeing something obvious that I'm missing completely ?? besides my incompetence, if yes keep asking ?? don't just give the answer. Going back this actually quit while it was in standby mode , just plugged in with the clock,should I be focusing on IC401? no signal to amplify ?. This unit isn't worth a free lunch to start with , thought it would be a good solid state learning tool, and it has been with the patience of the supporting members here .
    Last edited by shortcircuit; 04-03-2018 at 10:05 PM. Reason: +

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    I think you are correct, look at IC401.
    If you are hearing hum and the volume control seems to make an audible change, the power amp is probably ok. I assume you listened to the phones and didn't hear anything there either?
    And you said the fault was originally intermittent, have you tapped around with a chopstick to see if there is a physical connection issue?
    There are some DC voltages listed for IC401 on page 20 of the service manual. Also check for any audio at the L & R output pins. If you do have audio there, then you can return to the power amp.
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    Quote Originally Posted by g1 View Post
    I think you are correct, look at IC401.
    If you are hearing hum and the volume control seems to make an audible change, the power amp is probably ok. I assume you listened to the phones and didn't hear anything there either?
    And you said the fault was originally intermittent, have you tapped around with a chopstick to see if there is a physical connection issue?
    There are some DC voltages listed for IC401 on page 20 of the service manual. Also check for any audio at the L & R output pins. If you do have audio there, then you can return to the power amp.
    Hear a hum ,and low audio clicks when volume is increased ,no audio increase , correct nothing from headphones. Here is the only ic401 voltage chart I have , and my readings
    401.jpg I don't trust the chart, voltage chart for ic501 wasn't even close. Wouldn't it be odd that both audio IC's go out ?. Thanks for the reply

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    Well, hopefully it's the correct schematic, otherwise we're probably beat.
    Look at the audio switching IC page (pg.13 of pdf), there should be 6.8VDC coming in on pin 4 of P301 connector. Do you have that? You have nothing on pin 24 of IC401, which is supposed to be the supply pin. The unit is not in stand-by mode is it? Does the part number on IC401 match what the schematic shows, TDA7440 ?
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    Quote Originally Posted by g1 View Post
    Well, hopefully it's the correct schematic, otherwise we're probably beat.
    Look at the audio switching IC page (pg.13 of pdf), there should be 6.8VDC coming in on pin 4 of P301 connector. Do you have that? You have nothing on pin 24 of IC401, which is supposed to be the supply pin. The unit is not in stand-by mode is it? Does the part number on IC401 match what the schematic shows, TDA7440 ?
    yes IC401 is correct , confident in schematic it came from The Dude post #5 , voltage charts are just goofy. Do not have 6.8vdc , have .765vdc on pin 4 so I have a good connection between pin 4 of P301 and pin24 of IC401, just no voltage , have my 11.71vdc on pin 2 .01 on pin 7 and 4.44vdc on pin 10 . 0vdc on the rest
    unit is on FM radio tuned to a station less than 2miles down the road, no headphones plugged in , not in standby according to display. move on to cassette board , .765vdc on pin 4 of N302 , following pin4 from n301 and pin 1 on n302, not familiar with points symbol
    Last edited by shortcircuit; 04-05-2018 at 02:12 PM. Reason: -

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    Supporting Member The Dude's Avatar
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    If you don't have the 6.8V supply on pin 24, IC401 won't work. Look down below IC401 on the schematic at Q401. Do you have the 10V supply going to the collector (P101 connector)? Also check the emitter voltage just in case R420 is open.
    “Yeah, well, you know, that’s just, like, your opinion, man.”

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    Quote Originally Posted by The Dude View Post
    If you don't have the 6.8V supply on pin 24, IC401 won't work. Look down below IC401 on the schematic at Q401. Do you have the 10V supply going to the collector (P101 connector)? Also check the emitter voltage just in case R420 is open.
    Yes I have 11.73vdc at the collector of Q401 , .780vdc at the emitter, 7.56 at the base. 11.75vdc at P101. R420 56ohms

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    You should have about 6.8V at Q401 emitter. Replace Q401.
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    Quote Originally Posted by g1 View Post
    You should have about 6.8V at Q401 emitter. Replace Q401.
    Looking for a replacement as you replied, thank you very much
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