Larry's Phase Linear 700B

[laatsch55]

Once again thanks Doug. And I was serious about changing out the LED's.

 

[mlucitt]

We know one thing fur shur. The PL will not take 6.5V on the input for very long.

Mark

 

[orange]

Not sure anybody's already answered this before, but since this is a thread about Larry's amp,

WHERE THE HELL IS LARRY?

Did I miss something? Get his butt back posting!

 

[laatsch55]

Steve I think he's takin a break.

 

[laatsch55]

We know one thing fur shur. The PL will not take 6.5V on the input for very long.

Mark

Longer than a 13 volt square wave.

 

[laatsch55]

Joe, I'm trying to decipher why Q4 has 100 volts on the collector, and from studying the schematic, the way I see it is if D4,D5 get blown through. but they can handle 100. If Q5 took a hit, then R14 or R16 would had to give up the ghost also. If C5 got shorted, R11 would have had to go too. Am I barking up the right tree??

 

[Gepetto]

Lee
Are you sure you are looking at the collector of Q4? The pinout is E-B-C from left to right when looking at the flat on this transistor. Opposite pinout from the TIS 97 devices that you normally use for Q1 and Q2. The collector of Q4 should be closer to -100V unless the trace connecting Q4-C to Q5-B blew off the board.

 

[Gepetto]

And you are barking up the right tree Lee.

 

[laatsch55]

Yep. Collector. D5 was wounded, replaced Q5,Q7, C5 and D4 while I had them out.

 

[laatsch55]

yes the collector ties directly to D4 ,R11,R14, and the base of Q5. Q5 had -101 all the way around.

 

[Gepetto]

Let me know what turns up bad after you replace the parts Lee. D4 and D5 should have survived. Did R8 suffer any damage?

 

[laatsch55]

And after trying it again, still have 100 on the output. From A ground reference with the DMM on 5l, I'm getting PLUS 100 all the way through the protection circuit from the anode of D9 to the cathode of D10 and all points in between. And I might add, it goes up slowly like it has to charge a cap to get the 100 on the output. Hmmm.....

 

[laatsch55]

Joe D5 was wounded. .132 forward voltDC and .118 reverse volts DC.

 

[laatsch55]

On R8 I have 9.82v on one side and 9.85 on the other. With the DBT in line so it's gonna be a little low.

 

[laatsch55]

And the +20/_20 regulators are good.

 

[laatsch55]

Everything still points to Q5.

 

[laatsch55]

Got a weird short accross the base/collector of the minus RCA-410's. My meter shows in diode test mode OL short?? That coulkd be due to the 100 all accross the D9-D1- road there. It's not the drivers, pulled and checked them. BTWE that symptom is common to both channels.

 

[laatsch55]

Check that with Q12 out of the left channel I'm getting different reading on Q12 on the right channel. In diode test meter says 1.82 .........hang on ...

 

[mlucitt]

Lee,
I had the similar symptoms on my PL 700B. Did you lift one end of those clamping diodes D14 and D15? That' s how I found my shorted diode - B+ to the output.

 

[laatsch55]

No I haven't yet Mark, but it was on my to-do list.