phase linear 400

[Vynuladikt]

I am confused with your description of the timeline. You mention C8 being wrong and you corrected it but it tested fine. What is the value/type of C8, and where is it in the circuit?

 

[Gepetto]

Even more to the point Gene, what was in that kit that you swapped components out with? Can you provide the reference designators for each component you swapped?

You may have broken one or more of the leads on the bias transistor whilst doing your board rework. If you break a lead and the bias transistor becomes 'open' as a result, all hell will break loose on the back wall. And in the process of taking out (damaging them) the 4 outputs, you may have opened one or more emitter resistors which will make the subsequent DBT test look fine when it actually isn't fine.

 

[Vynuladikt]

I am confused with your description of the timeline. You mention C8 being wrong and you corrected it but it tested fine. What is the value/type of C8, and where is it in the circuit?

Went back through the thread, C8 would not have caused that failure. As Joe mentioned it probably was runaway bias. Time to find the culprit and trace damage. Or better yet, get a White Oak board.

 

[gene french]

The old CRTs were high voltage, but much lower joules/capacitance. Read as a mild pop. The PL 400 amps with 80 volts and 5900 uF on each rail can be used as welders. Upgraded power supply caps with 10,000 to 15000 will disintegrate a screwdriver. But I guess you know that now.

I am confused with your description of the timeline. You mention C8 being wrong and you corrected it but it tested fine. What is the value/type of C8, and where is it in the circuit?

100uf 25v...circled in pic...the top one i had reversed....
after recap....it played 4 or 5 seconds...then quit...was scratchy....
i noticed the cap reversed....i discharged the caps and switched it around...
has not played since...

 

[gene french]

Even more to the point Gene, what was in that kit that you swapped components out with? Can you provide the reference designators for each component you swapped?

You may have broken one or more of the leads on the bias transistor whilst doing your board rework. If you break a lead and the bias transistor becomes 'open' as a result, all hell will break loose on the back wall. You in the process of taking out the 4 outputs, you may have opened one or more emitter resistors which will make the subsequent DBT test look fine when it actually isn't fine.

here was the work sheet....i got one for the sx...much more professional and documented...

 

[Vynuladikt]

100uf 25v...circled in pic...the top one i had reversed....
after recap....it played 4 or 5 seconds...then quit...was scratchy....
i noticed the cap reversed....i discharged the caps and switched it around...
has not played since...

I think it was possibly blown when it quit playing after 4 - 5 seconds. again, I don't think C8 could have played any part of the failure.

 

[FredR]

Shorted the capacitor plus and minus accidently one time. Scared the shit out of me.

 

[gene french]

i was afraid of my sweaty hand getting too close to the cap....i discharged....
those are huge....after turning the amp off....it still played 6 seconds or so...
that scared me....thought jesus came for me...

 

[gene french]

Shorted the capacitor plus and minus accidently one time. Scared the shit out of me.

my son had the bubble wrap the light bar came wrapped with...and waited until i was elbow deep into the 400....started popping the wrap....
he slept outside....i had to change underwear....my wife is still laughing...

 

[gene french]

Went back through the thread, C8 would not have caused that failure. As Joe mentioned it probably was runaway bias. Time to find the culprit and trace damage. Or better yet, get a White Oak board.

or an error on my part ....i sent pics of both sides...of the driver board....
the dot map in the service manual has some bad spots...i did the best i could....
but, i feel i did somethiing on the 400c board...

 

[gene french]

here was the work sheet....i got one for the sx...much more professional and documented...

yes sir i certainly could have damaged something...and evidently did...

 

[WOPL Sniffer]

now how much fun would that be???
some enjoy the idea of exploring new avenues..
i am doing this for my pleasure and entertainment...
not an investment...

Yeah, sounds like fun

 

[gene french]

it gives me a chance to learn, improve, and get to know some nice people in the forums!!!

 

[WOPL Sniffer]

yeah.... I forgot..... The Big Boy Club

 

[gene french]

now you got the idea!!!
any idea on the 400c board???

 

[WOPL Sniffer]

now you got the idea!!!
any idea on the 400c board???

Don't know what a 400c board is, I use white Oak 14_20 boards. Anything else is old junk

 

[gene french]

Even more to the point Gene, what was in that kit that you swapped components out with? Can you provide the reference designators for each component you swapped?

You may have broken one or more of the leads on the bias transistor whilst doing your board rework. If you break a lead and the bias transistor becomes 'open' as a result, all hell will break loose on the back wall. And in the process of taking out (damaging them) the 4 outputs, you may have opened one or more emitter resistors which will make the subsequent DBT test look fine when it actually isn't fine.

is q6 the bias trans

here was the work sheet....i got one for the sx...much more professional and documented...

both q6s check fine in circuit....i will poke around a little more....so far i see nothing obvious...

 

[Gepetto]

now you got the idea!!!
any idea on the 400c board???

Sadly the PL 400C schematic that I have does not match the board you have Gene so the schem I have is kind of worthless for helping you. You sure you have a 400C?

 

[gene french]

Don't know what a 400c board is, I use white Oak 14_20 boards. Anything else is old junk

it written on the back of the driver board...

Sadly the PL 400C schematic that I have does not match the board you have Gene so the schem I have is kind of worthless for helping you. You sure you have a 400C?

here is a pic of the board

Sadly the PL 400C schematic that I have does not match the board you have Gene so the schem I have is kind of worthless for helping you. You sure you have a 400C?

Sadly the PL 400C schematic that I have does not match the board you have Gene so the schem I have is kind of worthless for helping you. You sure you have a 400C?

looks like 3 versions???
i have the hifi engine version of 1976

 

[gene french]

with no inputs or outputs connected to the 400
and no transistors installed in the back plane...
the dbtester lights on power up and immediately dims....as it should....
the new light bar lights as it should....
that is a neat bar....the adjustment was the touch!!!!

havent had a chance to check much else....
thanks ....