HELP! Rescuing Dad's old PL400 S2 (pics)

[laatsch55]

No need to worry about discharging the PS caps yet....we're a loooooooooooooong way from putting power to this puppy....

 

[lightfall]

roger that, thanks. I will update here as soon as I do the tests you suggested. Sorry for the post edit, that was sloppy of me.

 

[Northwinds]

You have a mess, it would be cheaper to get the WO board populated and all new transistors. There is no cheap fix for the 400. Popping a 14A fuse where a 5A is supposed to be, as Lee said, is BAD. I would not even think about powering that beast up unless you need some extra illumination and heat for a microsecond or two. My first 400 was worse then yours though so take heart, she will live to sing again

On a side note, how the amp sounds is irreverent in stock configuration. It will sound ok to you but once you go Full Comp, there is no comparison, it's like night and day the difference between a stock PL and a WO'd one

Welcome aboard Brother!

 

[laatsch55]

I'm irreverent....I don't think the amp is.

 

[Northwinds]

I'm irreverent....I don't think the amp is.

You know what I mean Lee

 

[laatsch55]

Yes I do. Can't help giggin ya though...

 

[gadget73]

hmm, someone has been doing naughty things. Overly large fuses and mismatched output transistors is a no-no.

One nice thing about the PL manuals is they explain the troubleshooting process fairly well. The first solid state amp I ever did any real amount of work on on was a PL 700-II. Its basically just the big brother of what you have in front of you, not terribly different other than its just got more transistors on the back. I was able to find the bad outputs, and with help from the guys here and on AK, I got it back together with a complete set of new output transistors. I also did some other troubleshooting to fix distortion and oscillation problems, but that turned out to be just some bad resistors. All in all, I wouldn't say these are a terrible amp to start with. They're pretty simple inside, and physically they aren't horribly difficult to deal with. You can actually access everything you need to access, which is more than I can say about some things.

 

[lightfall]

I really appreciate the feedback, I am committed to restoring this unit now, so forgive my ongoing newbie questions but I will get a handle on this. It holds sentimental value for me, and I have always loved the way it looked. My Dad would have rather had the 700 unit, but he says I was born and he had to save a little cash...heh.

I am going to start testing the outputs today with my multimeter after re-reading the manuals and will report back with the results. I am really tempted by the suggestions to just buy the WO replacement board, but at $170 it isn't cheap. I think I would still have to replace many of the emitter resistors that are cracked anyway, and I would worry about ruining a brand new $170 part. And I will have to match up the output resistors since mine are all mixed it seems. The fuse issue of course scares me as well; I checked with my Dad, apparently there was a business here in town that specialized in phase linear and stereos who last touched the unit, they are no longer in business. I don't know why the outputs would have been mismatched and why those ridiculous fuses would have been installed and he cannot recall either.

So where do I buy the output transistors, mica insulators, emitter resistors, and test equipment and such?

Do you think any damage could have occurred in the capacitors and power supply? What do I refer to the brown square units with the emitter resistors on it on the inside opposite the outputs? And the yellow circles on the control board a few appear to have small cracks in them, does that make them bad and what are they referred to as?

 

[laatsch55]

The ceramic disc capacitors on the board are fine. The brown things on the back wall are SOCKETS . The power supply caps rarely fail. Neither does the transformer. The bridge rectifier ( the small square thing between the PS caps ) sometimes will. Don't worry about buying any parts yet. They need to be identified first and you need to know enough to order the right thing.

 

[lightfall]

I am adding a picture of the preamp; it cleaned up really nicely. My Dad says it was working well last he checked, so I am going to not mess with that aside from attaching a new power cord end. Unless you think I need to do a run down of that unit as well. It was very clean inside.

 

[laatsch55]

One thing at a time. You are going to need to need to get some De-oxit for pots and switches. You get it at Parts Express.

Caig De Oxit. 2-1/2 ounce spray can of D-100 and a 5 ounce spray can of D5.

 

[laatsch55]

Ron. I'm in the field. Could you link AKs testing transistors basics thread here?

 

[lightfall]

Is it this thread? http://www.audiokarma.org/forums/showthread.php?t=43186

 

[laatsch55]

That's the one. That's for testing single transistors out of circuit.

 

[NavLinear]

Another link to AK - MTF transistor advice.

http://www.audiokarma.org/forums/showpost.php?p=8197765&postcount=85

 

[lightfall]

I am going to have to re-read this 10 more times to understand it. Are there any picture diagrams anyone knows of the specific components on THIS unit that I should be testing in my particular scenario? I haven't even gone back down to the basement with the multimeter yet I just keep rereading these posts trying to understand the concept and how it relates to the practical problem at hand.

 

[laatsch55]

It doesn't until you start pulling individual components. For now follow the service manual on testing the output transistors. It's a very well written manual for troublke shooting. Test the outputs and get that narrowed down, then we move on. We're not gonna be jumping all over and doing things 3 times. We're going to systematically go through the steps..

 

[MarkWComer]

I do not have a..., dim bulb tester,....

The DBT is something you'll build for yourself. It's a simple circuit and there aren't many parts to it.



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[lightfall]

Quick point of clarification: "Connect the negative lead of your DMM to the collector bus wire on the left bank of outputs, then check at the transistor side of the emitter resistors for each output."

Which wire is the collector bus wire? I assume it is a wire near the brown sockets on the left inside panel.

Also, which is the transistor side of the emitter resistor? I have a few, I think, of these that are cracked on the set of 8 sockets for the right side of the case.

 

[laatsch55]

Look at the row of sockets on the left.....the bus bar with the black cylinder on it is the BASE bus bar.....mewaning it connect all the BASES of the output transistors together. The bus bar to the right of it is the COLLECTOR bus bar. Put your negative lead on that bus bar. Those brown resistors are emitter resistors. Where they tie to the terminal strip is where you put the positive lead. A normal reading is around 10 ohms. A shorted output will show less than one ohm usually...

Do this on all 4 rows of sockets...the 2nd and 4th rows have the COLLECTOR bus bar on the left of the BASE bus bar.