Schematic for RCA RS2640

[shortcircuit]

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

[The Dude]

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.

[shortcircuit]

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

[g1]

You should have about 6.8V at Q401 emitter. Replace Q401.

[shortcircuit]

You should have about 6.8V at Q401 emitter. Replace Q401.

Looking for a replacement as you replied, thank you very much

[The Dude]

I would first check the resistance from emitter to ground to rule out a near short on that 6.8V supply line. Something could be shorted loading down that supply.

[shortcircuit]

I would first check the resistance from emitter to ground to rule out a near short on that 6.8V supply line. Something could be shorted loading down that supply.

powered up 11.98 M ohms ,powered off starts around 3k and climbs I quit around 10k and climbing.

[The Dude]

Ok, firstly, don't ever measure resistance with power applied. You could cause more damage. If you measured a short it would be zero ohms or something near. Infinite is no resistance or open. Since you measure above 10k or in the M ohms, I don't think we have a short, so go ahead and replace the transistor.

[shortcircuit]

Ok, firstly, don't ever measure resistance with power applied. You could cause more damage. If you measured a short it would be zero ohms or something near. Infinite is no resistance or open. Since you measure above 10k or in the M ohms, I don't think we have a short, so go ahead and replace the transistor.

Thank you ftkita, lesson learned , I don't have a suitable replacement on hand , only npn I have are 2n3904's

[The Dude]

The 2N3904 is rated for only about a quarter of the current as the original part. I doubt it would last. FYI, here's a datasheet for the original part.

http://pdf.datasheet.live/datasheets-1/kec/KTC3203Y.pdf

[shortcircuit]

The 2N3904 is rated for only about a quarter of the current as the original part. I doubt it would last. FYI, here's a datasheet for the original part.

http://pdf.datasheet.live/datasheets-1/kec/KTC3203Y.pdf

believe it or not I actually figured that out 200ma instead of 800,( wondered on a formula for emitter current usage with voltage info I have)but doubted it was going to be that low , have to order transistor , so it will be a few days before we get any results , again can't thank all supporters enough....on to a 70's vibro champ

[The Dude]

I don't usually recommend NTE parts because they're often a poor cross and cost more than original parts most of the time. That said, since this transistor has to match nothing, you might think about using an NTE or ECG 382. It's rated higher and has a bigger body to dissipate more heat. You might even have a dealer nearby saving you shipping cost making it cheaper than ordering. The basing diagram is also the same.

[shortcircuit]

I don't usually recommend NTE parts because they're often a poor cross and cost more than original parts most of the time. That said, since this transistor has to match nothing, you might think about using an NTE or ECG 382. It's rated higher and has a bigger body to dissipate more heat. You might even have a dealer nearby saving you shipping cost making it cheaper than ordering. The basing diagram is also the same.

thanks for the info, dealer near me, I WISH, one horse town, two weeks from everywhere

[The Dude]

[shortcircuit]

I don't usually recommend NTE parts because they're often a poor cross and cost more than original parts most of the time. That said, since this transistor has to match nothing, you might think about using an NTE or ECG 382. It's rated higher and has a bigger body to dissipate more heat. You might even have a dealer nearby saving you shipping cost making it cheaper than ordering. The basing diagram is also the same.

Finally received NTE382 to replace Q401 , Success !!! we have audio. Thanks to all the support members for your patience and knowledge , I learned a lot on this one.