(Now that I can post this as a new thread, I am doing so to hopefully get more replies)
I loaned my PL 400 Series 2; when I got it back it had blown protection fuses. Three output transistors (using the service manual procedure) showed as bad (shorted). I had used it the day before loaning without problems.
The outputs are relatively cheap (ON 15024) ... about $5 each. Would it be worth just changing all of them on the bad channel, or is there a good possibility that other parts are bad? Last time it was serviced it had only bad outputs, but that was back in 1988.
I did take it to a recommended local service outlet, but they don't agree with all the service bulletins regarding transistor substitutions, and I really don't know if they know what they are doing. They say six outputs are bad, though. They want to use NTEs. My old really good service tech is out of business.
My thinking is to try changing them all and sending it to a Phase Linear expert if that doesn't work, unless someone here has some hints otherwise.
Thanks,
Richard Wagoner
I loaned my PL 400 Series 2; when I got it back it had blown protection fuses. Three output transistors (using the service manual procedure) showed as bad (shorted). I had used it the day before loaning without problems.
The outputs are relatively cheap (ON 15024) ... about $5 each. Would it be worth just changing all of them on the bad channel, or is there a good possibility that other parts are bad? Last time it was serviced it had only bad outputs, but that was back in 1988.
I did take it to a recommended local service outlet, but they don't agree with all the service bulletins regarding transistor substitutions, and I really don't know if they know what they are doing. They say six outputs are bad, though. They want to use NTEs. My old really good service tech is out of business.
My thinking is to try changing them all and sending it to a Phase Linear expert if that doesn't work, unless someone here has some hints otherwise.
Thanks,
Richard Wagoner
Hard to tell why an amp blows up.
It could have had a low impedance peak, loose TO3 cans, a bad soldering...
They take out other parts, randomly.
That's why you need to check all other transistors and diodes too.
Look for burnt resistors and replace the (I think two) electrolytes on the driver board.
/Hugo
It could have had a low impedance peak, loose TO3 cans, a bad soldering...
They take out other parts, randomly.
That's why you need to check all other transistors and diodes too.
Look for burnt resistors and replace the (I think two) electrolytes on the driver board.
/Hugo
Its possible the outputs originally got taken out from other problems in the circuit and vise versa. Some typical blown output occurences would from shorted speakers and connects, being over driven or impedance loading etc.. I would use NTE as a VERY LAST resort. As Hugo suggested be sure to check the other semis like the drivers, diodes, and look for burnt/open resistors (you don't want to blow up new outputs needlessly). Its wise to replace the entire channel. I honestly don't know if these require matching. Search the forum, I believe there are some other threads on these PL400's regarding the outputs and substitutes.
edit: some good info here also http://hometown.aol.com/PhaseTek/
edit: some good info here also http://hometown.aol.com/PhaseTek/
Take your time to wade through this nice site. There's a wealth of info from first hand.
http://hometown.aol.com/phasetek/
/Hugo
http://hometown.aol.com/phasetek/
/Hugo
I've asked around, and my old tech is nowhere to be found. I don't remember his last name, unfortunately. His first is Mike, and the busines was The Sound Eye in Torrance, CA.
Nothing is burned; nothing smells burned either. But I haven't gone too far into it. I need to get it back from the hacks, though ... I pick it up unrepaired Monday.
Thanks for everything so far!
Richard
Nothing is burned; nothing smells burned either. But I haven't gone too far into it. I need to get it back from the hacks, though ... I pick it up unrepaired Monday.
Thanks for everything so far!
Richard
I picked up the amp today. They found the same bad output transistors that I found; at least they did want to change all 6 rather than just the bad 3. They said they checked everything and that the outputs were all that was bad. I don't necessarily believe them. Interestingly, they switched one of the driver transistors with an output transistor on the "good" channel; I'll have to switch that back.
Now ... should I buy MJ15024, or would the MJ21196 be a good upgrade? (supposedly more able to dissipate heat).
Now ... should I buy MJ15024, or would the MJ21196 be a good upgrade? (supposedly more able to dissipate heat).
Hi Richard,
This would be a great time to strip the entire amp. Separate the bad transistors (all from the bad channel) and strip, then clean the heat sink assembly. Clean the old transistors completely. Reassemble the "good" channel and use new mica heat sink insulators and thermal compound. Do not fail to use new stuff here!! Repeat the same process for the blown channel, installing new transistors. Clean the new parts first, do not assume they are clean. Snug up the parts without "cranking" them down too tight. Motorola (On Semi) has an information sheet on this. I think the pressure was around 8 inch pounds (that's not much!).
Before cheaping out on replace the parts you should, please consider this. One bad insulator, bad grease (the original stuff) or a bad transistor can blow the entire lot. Even if it didn't and you were able to prevent further damage, you would have to redo the job. Your time is worth something. Don't forget to check the emitter resistors and base resistors (if used) while the transistors are out! Also test the bias transistors and any protection transistors while the heat sink is out and things are easy to get to. Make it easy on yourself.
Replace the smaller electrolytics while you are there. You will hear the difference.
-Chris
I hate to say this, but you must replace all the outputs and drivers on the blown channel. Sorry. Like numbers should be matched for beta. Some would match VBE, but they will match from the same lot. Buy from Digikey or Newark.
They may have attempted to power the amp up by switching parts around. Very bad practice! Check that driver very, very carefully. You really ought to simply replace it though.
MJ21193 and MJ21194 or MJ21195 and MJ21196. These are slower than the MJ1502(2,3,4,5). I like these parts but they may cause issues in your older amp.
This would be a great time to strip the entire amp. Separate the bad transistors (all from the bad channel) and strip, then clean the heat sink assembly. Clean the old transistors completely. Reassemble the "good" channel and use new mica heat sink insulators and thermal compound. Do not fail to use new stuff here!! Repeat the same process for the blown channel, installing new transistors. Clean the new parts first, do not assume they are clean. Snug up the parts without "cranking" them down too tight. Motorola (On Semi) has an information sheet on this. I think the pressure was around 8 inch pounds (that's not much!).
Before cheaping out on replace the parts you should, please consider this. One bad insulator, bad grease (the original stuff) or a bad transistor can blow the entire lot. Even if it didn't and you were able to prevent further damage, you would have to redo the job. Your time is worth something. Don't forget to check the emitter resistors and base resistors (if used) while the transistors are out! Also test the bias transistors and any protection transistors while the heat sink is out and things are easy to get to. Make it easy on yourself.
Replace the smaller electrolytics while you are there. You will hear the difference.
-Chris
Bigred said:It seems like quite a few have had good success with the MJ15024's. Why mess with success
No real reason; I just read (here I think) that MJ21196's are electronically identical but dissipate more heat. Digi-Key has them both for a good price (MJ15024G for $4.73; MJ21196G for $3.78; I assume the "G" version is fine ... I hope)
Richard
Hi Bigred, Richard,
Look at the fT. You really want to use the slower parts. Those would be the MJ2119X part numbers. I have had issues with oscillation using the MJ1502X parts. Remember, I like the MJ1502X numbers a lot. Just not in older amps that used slower outputs originally.
Using those faster transistors would be messing with success.
-Chris
Simple.
Look at the fT. You really want to use the slower parts. Those would be the MJ2119X part numbers. I have had issues with oscillation using the MJ1502X parts. Remember, I like the MJ1502X numbers a lot. Just not in older amps that used slower outputs originally.
Using those faster transistors would be messing with success.
-Chris
Hi, Chris.
I had read that in the service manual, so I did plan to do so. What amazed me is that the repair place actually knew that. Perhaps because I left the service manual with them!
Ooh, I hadn't thought if that. Is there a good replacement for RCA 410's? Should I replace both in the channel? I don't have an actual transistor checker.
The other channel has NEC 2SD555. Are they any more different than MJ21196 compared with the original MJ15024?
I did not see any grease on any of the outputs, either side (actually, I did not remove the "working" side outputs myself, so I will have to look). There are insulators.
I think I may have some fun with this.
By the way, what is the difference between quasi-complementary, as mine is, and full complementary output stages? I have the service bulletin that shows how to make the change, but is it worth making the change?
Richard
anatech said:
I had read that in the service manual, so I did plan to do so. What amazed me is that the repair place actually knew that. Perhaps because I left the service manual with them!
Ooh, I hadn't thought if that. Is there a good replacement for RCA 410's? Should I replace both in the channel? I don't have an actual transistor checker.
The other channel has NEC 2SD555. Are they any more different than MJ21196 compared with the original MJ15024?
I did not see any grease on any of the outputs, either side (actually, I did not remove the "working" side outputs myself, so I will have to look). There are insulators.
I think I may have some fun with this.
By the way, what is the difference between quasi-complementary, as mine is, and full complementary output stages? I have the service bulletin that shows how to make the change, but is it worth making the change?
Richard
Hi Bigred,
Slower than the MJ1502X types. I'm sorry, I seem to disagree with you a lot. This is not by intent.
It's very good practice to use a part as close to the specs of the old one as possible. A few years ago I would have said the same thing that Nelson did. The MJ2119X parts were not out yet and so there was no choice. And yes, I did have to work with the compensation on more than one amp. The Japanese amps were no problem as their parts were typically much faster than US parts anyway.
Some circuits are tolerant of a faster part, some aren't. Why go looking for trouble? My Marantz 300DC could use either. An older amp like a Crown DC300 wouldn't take kindly to faster parts. A Marantz 240 may not either as it used slower parts.
Also, MJ15003 / MJ15004 are pretty tough. If you exceed the SOA on those, you may have easily done so with the MJ15024 and MJ15025. I used both types extensively and so could use either. I learned the hard way to look carefully at what you are replacing before just sticking in a TO-3 power transistor.
If Nelson used the MJ1502X numbers without problems, good. I just think you may be closer to "the edge" with those.
-Chris
Slower than the MJ1502X types. I'm sorry, I seem to disagree with you a lot. This is not by intent.
It's very good practice to use a part as close to the specs of the old one as possible. A few years ago I would have said the same thing that Nelson did. The MJ2119X parts were not out yet and so there was no choice. And yes, I did have to work with the compensation on more than one amp. The Japanese amps were no problem as their parts were typically much faster than US parts anyway.
Some circuits are tolerant of a faster part, some aren't. Why go looking for trouble? My Marantz 300DC could use either. An older amp like a Crown DC300 wouldn't take kindly to faster parts. A Marantz 240 may not either as it used slower parts.
Also, MJ15003 / MJ15004 are pretty tough. If you exceed the SOA on those, you may have easily done so with the MJ15024 and MJ15025. I used both types extensively and so could use either. I learned the hard way to look carefully at what you are replacing before just sticking in a TO-3 power transistor.
If Nelson used the MJ1502X numbers without problems, good. I just think you may be closer to "the edge" with those.
-Chris
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