Phase Linear 400 Repair

[Brettl]

New here, I ordered the White oaks board and Power supply, should be here this week. I also just purchased a Variac.

I have built a tube preamp in the past and multiple crossovers, I can solder quite well. I also know enough to be dangerous.

The 1st question I have is:

1) on the output board there are 16 Outputs if I take them out 1 by one can I test them with an Ohm meter to see if any are burned out? The current should only flow one way correct? If two ways the output would be defective correct? What should the ohm meter be set on ( I have heard 10K ohm but my meter does not have that setting )?

OK, Let me rewind for a minute:
This amp was running fine when I bought it other than a faulty VU meter and lights ( i did plan on upgrading ), I installed the White oaks light upgrade kit and I broke a golden rule. I was buttoning up the amp and wanted to make sure the meters were working ( power on, I know very dumb ) as I was screwing down the last wire to the back of the meter the wire flung back and hit the board ( the little thing that looks like a flower, then a large bang through the speakers, fuses blew and then no power to the one channel ).

So now I figure to just rebuild the main board and power supply as I wanted to anyway but I don't want to build the board only to blow it out. Looking for help as I get started. I also bought a second PL400 as a parts unit, to my surprise this amp also powers up but only also plays music from one side.

Looking forward to this project and any support you can lend.

Thanks, Brett

 

[laatsch55]

Pull and test the outputs on the non-functioning channel. It sounds like one of the meter wires that comes from the output stage to drive the meters shorted against the ground. You will probably find at least one output from each vertical row blown. Do you know how to test bi-polar transistors?



BTW....one of the few ways i HAVE NOT blown up a 400!!

 

[Fishoz]

You came to the right place for PL help. These guys know their shit!

And.....welcome! Why don't you hit introductions and tell us a bit about yourself.....we need ammo!!!

 

[Brettl]

Do you know how to test bi-polar transistors?

Well not really other than what I read, could you please give me the procedure again

Thx​

 

[Brettl]

You came to the right place for PL help. These guys know their shit!

And.....welcome! Why don't you hit introductions and tell us a bit about yourself.....we need ammo!!!

I added a small snippet.

 

[Brettl]

New Variac & the right side board damage & culprit with his scar! ( see arrows ). The channel now just has a solid buzz and the meter is pegged full out.

 

[Gepetto]

New Variac & the right side board damage & culprit with his scar! ( see arrows ). The channel now just has a solid buzz and the meter is pegged full out.


View attachment 20466 View attachment 20467 View attachment 20468

Well each meter red lead is ground and you shorted the collector of Q7 to ground likely shorting it out and causing the negative half of the amp to be driven active all the time (meter peg). Meter pegged on both channels?

Are you blowing the rail fuses?

 

[Brettl]

Well each meter red lead is ground and you shorted the collector of Q7 to ground likely shorting it out and causing the negative half of the amp to be driven active all the time (meter peg). Meter pegged on both channels?

Are you blowing the rail fuses?

Just pegged on the one side ( one meter, i think the right ). Yes, blowing fuses! Yes, bad mistake

 

[Brettl]

Looked great for 10 minutes. LOL

 

[Northwinds]

There is an art to blowing up an amp, I salute and welcome you. Nav will send a medic shortly

 

[Gepetto]

Just pegged on the one side ( one meter, i think the right ). Yes, blowing fuses! Yes, bad mistake

Hi Brett
Well on the right channel, all outputs could be mortally wounded then. Take each out, using your DMM on the diode scale, check each junction.


DMM Red lead on Base, you should get approx. 0.65V to the Emitter and Collector when touching with the DMM Black DMM lead
DMM Black lead on Base, you should get infinity or open to the Emitter and Collector when touching with the DMM Red lead
DMM Red lead on Emitter, you should get infinity or open to the Collector when touching with the DMM Black DMM lead
DMM Black lead on Emitter, you should get infinity or open to the Collector when touching with the DMM Red DMM lead

Repeat for all 8 devices in that channel. Mark any defective ones with a magic marker, a big black X on the back side of the case.

If you find a single bad device in the channel, replace all of the upper 3 rows with MJ21196 instead of the original PL909 transistors. If you find a bad device in the bottom row, replace BOTH right channel devices with RCA410 transistors in this location only.

Clear? If not, come back with questions and we will get you more help.

 

[Gepetto]

Hi Brett
Well on the right channel, all outputs could be mortally wounded then. Take each out, using your DMM on the diode scale, check each junction.


DMM Red lead on Base, you should get approx. 0.65V to the Emitter and Collector when touching with the DMM Black DMM lead
DMM Black lead on Base, you should get infinity or open to the Emitter and Collector when touching with the DMM Red lead
DMM Red lead on Emitter, you should get infinity or open to the Collector when touching with the DMM Black DMM lead
DMM Black lead on Emitter, you should get infinity or open to the Collector when touching with the DMM Red DMM lead

Repeat for all 8 devices in that channel. Mark any defective ones with a magic marker, a big black X on the back side of the case.

If you find a single bad device in the channel, replace all of the upper 3 rows with MJ21196 instead of the original PL909 transistors. If you find a bad device in the bottom row, replace BOTH right channel devices with RCA410 transistors in this location only.

Clear? If not, come back with questions and we will get you more help.

Some pictures:

 

[laatsch55]

Joe, that 179 looks awfully fresh!!

 

[ksrigg]

MEDIC

 

[Gepetto]

Joe, that 179 looks awfully fresh!!

Farm fresh as they say Lee...I even have a pouch that I keep it safe in...

 

[laatsch55]

Mine too, but I have taken it to the field a few times and have not cleaned it up afterwards...

 

[R1200S]

This is obviously not the right thread for this but I have to ask. I have a couple of rebuilds in my future and I'm in the market for a new multimeter before I get started. (Landed a screamin deal on a 15 amp variac!)
Fluke always seems to be the default out there. Is the 179 a good choice and will it do what's needed for the PL rebuilds? Any other DMMs pop in your mind as a good choice? Would more than 1 DMM be a good way to go?

Thanks!

 

[Brettl]

I just did 2 so far. I watched a few videos on U tube and I know this stuff is so basic but I am still not sure if this is right... here goes. I am holding the black lead to the casing of the unit and touching the red lead to each pin.

U tube I watched, forward to minute 11:52 this is the process: https://www.youtube.com/watch?v=nxuRSEtjaCo

So...do I have to do all tests on each?

Unit 1 has no black dot unit 2 has black dot ( see arrow )

1) looks good from the test - Please confirm
2) has a black spot - looks bad please confirm

 

[laatsch55]

Ok, basics again. All your outputs are original PL correct?

 

[laatsch55]

In pic #3, the red lead is on the BASE lead, and the black probe is on the case or COLLECTOR. The other lead sticking up is the EMITTER lead. In an NPN bi-polar transistor the BASE lead should have the red probe and the EMITTER, COLLECTOR leads should have the negative probe. With you DMM in diode test mode those two measurements should be around .(point) 560DC volts.