PL-700 OTW

[VSAT88]

Phase Linear 700 series 1 amps built from January 1971 until approximately July 1973 all used a PL0171 pc board.

I have (2) very rare 700's made in 1970 with two different pc boards which came out before the PL0171's did.

Ed

Exactly, this board is the PL0171.

 

[VSAT88]

Also check Q7, D3/4... I've seen q7 cause that issue or something down there in that circuit. Look at the schematic, there are voltage measurements on the schematic. Slow and steady. And, don't slip.... KABOOOOOOM

Done and it all tests good...

 

[WOPL Sniffer]

Done and it all tests good...

Did you try cleaning the bias adjustment pot? And measure it?

 

[VSAT88]

Did you try cleaning the bias adjustment pot? And measure it?

I did clean it but test it I did not. I will do so and get back with. Thanks again.

 

[VSAT88]

You are right Perry. I will just have to wing it. None of the drawings I can find are clear enough to read. I wonder If there is somewhere I could buy one ? If anyone can help with that please let me know.

 

[Northwinds]

Ed should be able to hook you up with a readable schematic (if anyone can)

 

[VSAT88]

Ed should be able to hook you up with a readable schematic (if anyone can)

Check that, Oldphaser it is. Thanks.

 

[VSAT88]

L chan. bias Pot reads 17.4 Ohms open all the way. The Right chan bias pot reads 10.5 all the way open. That is 7 ohms, a lot. I think I should pull them out of the board and check them. Should I do so ?

 

[oldphaser]

I will check out my collection of Phase Linear 700 and 700/700B service manuals and get back to you later.

Ed

 

[VSAT88]

L chan. bias Pot reads 17.4 Ohms open all the way. The Right chan bias pot reads 10.5 all the way open. That is 7 ohms, a lot. I think I should pull them out of the board and check them. Should I do so ?

Went ahead and pulled them both. Out of circuit they read the same.

 

[laatsch55]

Now you know....

 

[VSAT88]

Now you know....

Yes I know. I know how little that I know and I know why you guys WO instead of trying to repair these really old amps !

 

[laatsch55]

Check the resistors and caps around the VR...

 

[laatsch55]

And for broken wires...

 

[THD+N]

Phase Linear 700 series 1 amps built from January 1971 until approximately July 1973 all used a PL0171 pc board.

I have (2) very rare 700's made in 1970 with two different pc boards which came out before the PL0171's did.

Ed

THOSE would be the grand dad of Kaboom...

 

[oldphaser]

I will check out my collection of Phase Linear 700 and 700/700B service manuals and get back to you later.

Ed

OK its later now.......

I scanned the schematic from a first generation copy of the 700 service manual. Unfortunately the original schematic is a little blury.

So I spent some time generating a parts list for the resistors and capacitors used on the PL0171 pc board over the years since that is where most of your questions about component values will probably be. If my memory serves me correct, there are some errors on the pc board layout as well as schematic. So, please double check everything very closely.

Ed

 

[VSAT88]

OK its later now.......

I scanned the schematic from a first generation copy of the 700 service manual. Unfortunately the original schematic is a little blury.

So I spent some time generating a parts list for the resistors and capacitors used on the PL0171 pc board over the years since that is where most of your questions about component values will probably be. If my memory serves me correct, there are some errors on the pc board layout as well as schematic. So, please double check everything very closely.

Ed

Thank you Ed. I am slowly going through it part by part and checking resistors, transistors, pots and caps. I think I may have found a bad capacitor.

 

[VSAT88]

Thank you Ed. I am slowly going through it part by part and checking resistors, transistors, pots and caps. I think I may have found a bad capacitor.

C 11 was/is bad. A 10uF at 50v. I replaced it and tried bias again. Bias still low on L chan. I am going to check DC offset now and try it all over again. Mr. Ed. Thank you again for the diagram, it is better than the one I had. Oh, and according to the "700 Board History" .PDF you sent it says this about C 11. "C11 47MF/40V and 10MF/50V - 10MF/50V on earlier units and 47MF/40V on later units".

 

[VSAT88]

Well now. Perry asked me if I had checked the fuses. I had at that time. Now after a many more attempts at this thing I re checked the fuses because as I said below, I was going to start all over. I checked them again. Low and behold, Left channel - rail fuse was blown. I do not have any replacements for this size so I took the good ones from the right and fired it up left channel only. DC offset looks good initially and if anything the bias is running a bit high.

 

[laatsch55]

Does it adjust?