PL400 PL20 REV E upgrade bias problem - help

sebtus

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#1
i just got the PL20 and i put it all together. i don't have the back plane just the PL20. once i got to the bias adjustment the left adjusted fine. Right channel however i get nothing. i get no reading at the test point. i verified all my work to make sure i did not install diode or cap in reveres position and it looks good for both channels. i dont know where to start looking since i do not have the diagram. I measured some voltages and what i know is this:
there is +-81vdc, + -15 vdc. and i get 0.6vdc at the left channel bias pot and 0.1 at the right one.

i have q6 and q9 readings but im not sure which is e b c but i hope this helps:

| o |
/ | \
1 2 3

Q6L: 1=1.4vdc, 2=81.5vdc, 3=0.88vdc
Q6R: 1=-0.64vdc, 2=81.4vdc, 3=0.224 vdc

Q9L: 1=0.62vdc, 2=-80.7vdc, 3=-0.010vdc
Q9R: 1=-0.124vdc, 2=-81.5vdc, 3=-0.012vdc

Q1: 1=15.6vdc, 2=81vdc, 3=15.1vdc
Q2: 2=-16.1vdc, 2=-81vdc, 3=-15.6vdc

not sure i that helps but here it is.


Any ideas where to start looking for the problem. Thank you
 
Last edited:

Gepetto

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#2
i just got the PL20 and i put it all together. i don't have the back plane just the PL20. once i got to the bias adjustment the left adjusted fine. Right channel however i get nothing. i get no reading at the test point. i verified all my work to make sure i did not install diode or cap in reveres position and it looks good for both channels. i dont know where to start looking since i do not have the diagram. I measured some voltages and what i know is this:
there is +-81vdc, + -15 vdc. and i get 0.6vdc at the left channel bias pot and 0.1 at the right one.

i have q6 and q9 readings but im not sure which is e b c but i hope this helps:

| o |
/ | \
1 2 3

Q6L: 1=1.4vdc, 2=81.5vdc, 3=0.88vdc
Q6R: 1=-0.64vdc, 2=81.4vdc, 3=0.224 vdc

Q9L: 1=0.62vdc, 2=-80.7vdc, 3=-0.010vdc
Q9R: 1=-0.124vdc, 2=-81.5vdc, 3=-0.012vdc

Q1: 1=15.6vdc, 2=81vdc, 3=15.1vdc
Q2: 2=-16.1vdc, 2=-81vdc, 3=-15.6vdc

not sure i that helps but here it is.


Any ideas where to start looking for the problem. Thank you
Hi Sebastian
You were sent a total of 19 documents the other day. Can you confirm that you received them?
 

laatsch55

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#5
sebtus, are you getting +,- 15 volts at the test points in the middle of the control board?
 

sebtus

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#8
update....
i could not figure out what was wrong with the new control board so i decided to install the original control board back in. Once i did that i tried to adjust the bias on the problematic right channel. once i turned about 1/8 of the trun counterclockwise the was a poof, smoke and spark on the control board. I noticed that one of the resistors went out of orbit and changed its properties to open. i checked output transistors to find three bad ones on the right channel. Moreover, i noticed that there were three replacement transistors, which made me think that there was a problem before, at some point. I up-channeled all my findings to White oak and as always i got prompted response saying that there is problem with the back-plane setup. Which made perfect sense, and who am i to question the professionals. i decided to go full speed and i ordered the back-plane kit with fullQ transistors. After about 6h of building two boards and another 8h of breaking the original setup down and installing new boards, wires, transistors and all that. it was time to test it.

Well, to keep it short i went step by step, checking voltages each time as i installed each row of transistors and all checked good. once all transistors were in i did bias adjustment and it worked.... easily adjusted to 0.35vdc. It is playing now... i hope it stays that way lol. I dont have my better speakers right now to check how it sounds but im sure i wont be disappointed.
It took a while and i know White oak is glad to final stop receiving emails from me. I figured i let everybody know how everything went and i wont leave this Thread unfinished.

Thank you Mr. Joseph King / White Oak for the help and great product.

Work done to the pl400:
new PL14 board
new backplane boards
new Full Quasi transistors
new filter caps
new LED lights
Protection board
new input connectors
new output connectors
new wires
 
Last edited:

sebtus

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#10
i have played the pl400 for a bit and it sounds nice. i noticed that one of my UV meters gets stuck on the negative side sometimes. Once i tap it comes back up,it works for a while and then it happens again. Any idea what could be the reason for that?
 

laatsch55

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#13
You might try cleaning the lenses with an anti static rag also, those plastic lenses can keep a buildup of static electricity ....
 

62vauxhall

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#15
There was a sticky meter problem with a 700B I experienced. The needle would rise but not fall all the way to rest. My thought was debris was the culprit but blowing from the mouth was ineffective.

I chose to use an small compressor with an air jet nozzle. To minimize damaging the meter's mechanism, I only charged up the compressor part way and took judicious care not to have the nozzle too close, at least not untill the air pressure was nearly depleted. This method might be frowned on but it worked.
 

sebtus

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#16
you think it is safe to use my pl400 to run ar98ls speakers.. they are 4ohm imp. speakers and i already have problems running them at their full potential with other amps(pioneer sx-1250, accuphase p-300--- not powerful enough). i dont want to overcook my new pl400. Can pl400 handle my speakers? what do you think, and what might happen if i push the amp to hard?
 

WOPL Sniffer

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#19
There was a sticky meter problem with a 700B I experienced. The needle would rise but not fall all the way to rest. My thought was debris was the culprit but blowing from the mouth was ineffective.

I chose to use an small compressor with an air jet nozzle. To minimize damaging the meter's mechanism, I only charged up the compressor part way and took judicious care not to have the nozzle too close, at least not untill the air pressure was nearly depleted. This method might be frowned on but it worked.

Ive seen this problem too but mine was a crusty switch for the attenuation. You could wiggle the switch and the meter would act correctly or not.... Replaced it and worked 4.0
 

WOPL Sniffer

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#20
don't use a compressor or BLOW inside the meters. DANGER DANGER WILL ROBINSON

I had a few meters where the 40 where old tape they used to tape the face onto the meter broke and the face was sticking up about a billionth of an inch. Is it catching on the face (not the cover)
 
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