Phase Linear 400 Series 2 Repair

[rwagoner]

(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

[Netlist]

Richard,

Change them all and make sure you have them from a good source.
Do yourself a favor and check all other semis AND diodes as well.
Replace the mica and grease and measure for shorts between TO3 cases and chassis.
Work patiently and accurately and use a variac.

/Hugo

[rwagoner]

Thank you.

In general on these, do the outputs usually blow themselves, or are they taken out by other problems? Or do they take out other parts? I have not had a problem since the last repair in 1988 or so, and the amp is used in a mobile DJ system.

Thanks again,

Richard

[Netlist]

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

[Bigred]

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/

[Netlist]

Take your time to wade through this nice site. There's a wealth of info from first hand.
http://hometown.aol.com/phasetek/

/Hugo

[poynton]

On my 400, all the emitter resistors had gone, either out of spec or cracked although none were burned.

I replaced them all with metal clad ones glued to the chassis.

Al the output transistors and a couple of the drivers had gone!


Andy

[anatech]

Hi Richard,

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.

Then, they are hacks. Run and never go back.

My old really good service tech is out of business.

I understand that. He may do work from his basement. Ask him if you can find him.

Hugo (Variac) is steering you in the right direction for sure.

-Chris

[jblmar]

Do you see any burned components?

Ron

[rwagoner]

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