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Where to buy replacement outputs

Ok, so that makes sense. Given that I have Sylvania ECG247 and ECG248 which do you think would have been used to replace the original Motorolas? Just going on the principle of number differences, I'd think the ECG247's were replacements for the SJ1902's and the ECG248's were replacements for the SJ1903's - can anyone confirm this for me? Or maybe the even-odd similarities...247's replaced the 1903's and 248's replaced the 1902's. AGH, I still have no clue. I don't guess there's any reading I can take on the outputs to determine which way they should be put in the amp?

I'm not familiar with doing a lot with outputs, but would these outputs actually work if they were installed backwards or does that literally toast something immediately? I wonder this because I question if the person who put these in might not have put them in backwards and that would explain the excessive heat generation.
 
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check all transistors and resistors and diodes in that channel if it was smoking no sense in making 2 orders and chancing blowing the outputs again .
 
Ah! I found it. So the ECG 247 is the NPN and the ECG 248 is the PNP. Which means the 2N6284 = ECG 247 and the 2N6287 = ECG 248. Great!

So as far as testing the other channel, I have powered the receiver up without any outputs in on that side and nothing gets hot. An examination of the amplifier board or whatever it is for the left channel shows no signs of anything not being correct. I don't think it would do me much good to go putting a meter on the stuff there because I have no service manual to know what values the diodes and such should be equal to.

Thanks for all this help guys, valuable information for me. I've never delved quite this technical into an amp before, I replaced a pair of STK Darlington power packs on an old Technics before but that was far less technical than this. I see this requires more tech sheet reading, but thanks so much for ID'ing the correct original outputs. No idea how you guys found that out, but it's very helpful to say the least!
 
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resistors have colour codes or its wrote on them .. transistors all test the same except darlingtons or fets or germanium which i doubt there are any . rectifier diodes will test same too .. except for zener diodes that generally have a higher reading on diode test .
if you check the bad channel against the good one you should see any faults . or you could try the good outputs in bad channel to see what happens ..you will be replacing all 4 after all .
 
Well, you were all very helpful - but yes Overload you did find the originals :p:

I did end up trying to swap the outputs. I put the good ones on the good channel on the side the bad ones were on - sounded very weak and crackly. So I put the good outputs back on the good channel - sounded fine. I put the bad outputs on the good channel...this was probably the stupid thing to do (Yeah I know...don't say it). In my defense, I wasn't sure the outputs were bad since the good outputs sounded crappy on the bad channel - made me think it was the driver board. I turned it on, got pure AC and in less than 1 second I saw something light up - I literally had enough time to turn it on, keep my hand on the knob, then turn it right back off.

Switched the good outputs back on the previously good channel - now it sounds crackly and weak just like the other side. So I'm under the impression something on the driver boards is bad. There are two metal transistors that are getting VERY hot on these boards (On the original bad channel, this is where the smoke was coming from) and I'm wondering if that's what's wrong. I lack proper test equipment to put a signal through and check it with a scope or I would. I tend to risk gambles on parts being bad as I have a friend with technical experience that recommends what's usually wrong - and he's usually right. He's suggesting those metal transistors are what's probably gone bad.

So would these two very hot transistors on the driver boards be what you all would possible suspect? Or has this proceeded to a level that I really need to take it to a technician? I'm perfectly able to desolder and solder new transistors in but without a schematic I have no idea what to test on the driver boards.
 
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My advice to you is to stop before things get any worse. Giving advice to put good parts from a working channel into a known problem channel is just moronic imo. Frankly there are a number of individuals throughout the forums who like to "help" people with their technical troubles but in all honesty, could REALLY help by simply sitting on their hands. Sounds harsh? You betcha! It needed to be said and I just said it :grumpy:
 
I think I really just need to stop buying vintage amps. While I've done well many times, I never have much trouble with newer equipment. While opinion may be (and truth may be) that a lot of BPC surround receivers aren't the most amazing sounding stuff, all the ones I've ever had worked. The only one that had issues had a volume knob issue that was rectified by using the remote. Even the cheapest, crappy looking receivers have worked ok. OTOH, I've had a great looking 9090 which was as dead as could possibly be imaginable for a piece of equipment, a 771 that looked great but has lots of issues, an old H/K that one channel intermittently works but sometimes doesn't and has no rhyme or reason for it, and now add the Sherwood to the list.

I know age brings on issues, but I don't really like having to operate on all my amplifiers. I wouldn't mind paying the money to have one restored, but not on a receiver - maybe for something like a nice vintage Threshold or Krell amplifier or something else very impressive but not just a receiver. Newer equipment may be more difficult to work on, but I have to give credit where due it fails far less often. You'd be amazed how much abuse a bass head friend of mine puts his beat up '90s Kenwood receiver through and it always works. Ah well, I'm going off on a tangent - the point is I appreciate all the help here, you're all a great resource for this kind of thing. I'll consider my options with the Sherwood, I'm not thoroughly convinced on repairing it personally so I may pass it off and just take my losses and consider it a learning experience (Don't switch in suspected bad outputs, putting a big check next to "Don't do this" :nono:)
 
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OverLoad said:
My advice to you is to stop before things get any worse. Giving advice to put good parts from a working channel into a known problem channel is just moronic imo. Frankly there are a number of individuals throughout the forums who like to "help" people with their technical troubles but in all honesty, could REALLY help by simply sitting on their hands. Sounds harsh? You betcha! It needed to be said and I just said it :grumpy:
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in retrospect i shouldn't have written it like that ..i was just trying to say what i said already and check everything on the driver board .as good outputs are likely to suffer plus more damage likely .
i will be more careful with my wording in future ..
 
Pete you're fine, I decided to swap the outputs on my own accord not based on anything anyone here said. I think Overload was just making a blanket statement about people who don't know what they're talking about (Like me :p:) telling people what to repair on their equipment, especially without having it in front of themselves. FWIW, I took what you said to mean use a meter on the blown channel's driver board and test everything on that to make sure if I bought new outputs that they didn't get toasted by the driver board.
 
Ok I revisited the amp, I still want to fix this and I'm suspecting these round silver transistors. There are two on each board, and for sure one is getting very very hot. I have no idea how to figure out what these are though. It says RCA in the middle, then around the edges looks like it says RCA/A10 or RCA/AID it's too hard to tell and it says CE 505. It does apparently pop out of the little socket, but I have no clue where to find info about this. This thing seems like it will be good for nothing but parts if I can't figure out what these transistors are - but without a service manual I have no clue and googling the transistor turned up absolutely nothing.

Any ideas, or is it done for and should I just move on?
 
Vistance said:
Ok I revisited the amp, I still want to fix this and I'm suspecting these round silver transistors. There are two on each board, and for sure one is getting very very hot. I have no idea how to figure out what these are though. It says RCA in the middle, then around the edges looks like it says RCA/A10 or RCA/AID it's too hard to tell and it says CE 505. It does apparently pop out of the little socket, but I have no clue where to find info about this. This thing seems like it will be good for nothing but parts if I can't figure out what these transistors are - but without a service manual I have no clue and googling the transistor turned up absolutely nothing.

Any ideas, or is it done for and should I just move on?
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Do you have a meter? You need to test the transistors.
I don't know what the transistors you are mentioning do in the circuit, but getting hot does not necessarily mean they are the problem. Something else could be drawing too much current through them. I'd suggest comparing the temperature to the good channel, but since you toasted it too...
Definitely sounds like you have blown outputs, and they took something else out when they blew. You then put shorted transistors in the good channel, shorting something else out there too. Next suspect would be the driver transistors. Fixing blown amps can be tricky, depending on how much has been damaged.
If you want to proceed, you definitely need a meter. Also soldering/desoldering equipment to remove parts for testing without damaging the traces.
I'd say you are better off taking it to a tech.
 
I have a meter with a transistor checker on it - but I haven't a clue which one of the legs is the emitter, the base, and all that. Nor do I know what the value should be. Wish I knew what did these outputs in. I was playing them on a pair of normal speakers, nothing special at normal volume levels. It always did get kind of hot, but this time it was very hot on the back and I was suspect of something being wrong with it. Then suddenly while it was playing, the receivers power just went off. It had apparently blown the fuse. When I put a good fuse back in it, smoke came out of it - but it didn't blow the fuse. So I'm not sure what to make of it.

At this point I'd just like to know what happened so I can see warning signs if it ever happens on another amp.
 
If there is <1ohm resistance (short) between any of the legs, it is bad. There is a thread around here somewhere about testing transistors, but a dead short is easy to identify.

There are a few things that can toast outputs. Could be the transistors themselves wore out. More likely the outputs were NTE crap replacements. Another is the bias pot going open. This results in way too much current going through the outputs, and frying them. The only warning sign you are likely to see is the one you saw, the unit getting much hotter than usual. You could do preventative maintenance, but I would not recommend messing with things you don't understand, you are just as likely to make it worse.

When you put a new fuse in, was it the same value? The fuse may not save all the components, but it will prevent further damage. When you put another fuse in, more short circuit current went through the outputs, further toasting things. If you used an overrated fuse, it would not have blown when it was supposed to, more short circuit current would have been allowed to flow, again toasting things further.
 
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The On Semi site is actually pretty good if you are are of the engineer persuasion. And some pn's are available as samples if you have those credentials....a nice thing! :D
 
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