phase linear 400

[gene french]

ok...as instructed....

both 10 ohm resistors are good....both 150 ohm resistors are good on left back plane
no inputs connected....no speaker outputs connected....
right channel is fully populated with the new transistors i just got from joe....left channel transistors checked and rechecked...4 were bad...tossed
left channel has the bottom row populated only....2 checked transistors in the bottom row on the left channel....i checked 95/96 location...all is correct...with them alternating with 96 closest to the transformer....
all fuses good 2 on back plane 2 on chassis on left side...and the main ac fuse also good...
dcprotect relay engaged....i watched the reeds....and the blue led lit after a few seconds...i watched the relay disengage when i powered down...and the blue led went out...
the relay is not welded....it is functioning properly....
b+ is +82.4 and b- is -82.4 on the back planes test points...both sides
+- 15v test points on control board are +- 15v...both sides
the left bias is 13 to 14 mv and does not respond to bias adjustment...
right bias is 365...as i set it the other day....still exactly where i left it...midway the recommendation of 350 to 380mv...
dbt bright then dim as expected....
meters lit....no response from needles upon relay engage...nor disengage
after the testing...i rechecked all fuses....they are fine...
i did NOT reinstall the legs i removed to confirm the bad emitter resistors and r1 and r3....

 

[MusicSteve]

ok...as instructed....

both 10 ohm resistors are good....both 150 ohm resistors are good on left back plane
no inputs connected....no speaker outputs connected....
right channel is fully populated with the new transistors i just got from joe....left channel transistors checked and rechecked...4 were bad...tossed
left channel has the bottom row populated only....2 checked transistors in the bottom row on the left channel....i checked 95/96 location...all is correct...with them alternating with 96 closest to the transformer....
all fuses good 2 on back plane 2 on chassis on left side...and the main ac fuse also good...
dcprotect relay engaged....i watched the reeds....and the blue led lit after a few seconds...i watched the relay disengage when i powered down...and the blue led went out...
the relay is not welded....it is functioning properly....
b+ is +82.4 and b- is -82.4 on the back planes test points...both sides
+- 15v test points on control board are +- 15v...both sides
the left bias is 13 to 14 mv and does not respond to bias adjustment...
right bias is 365...as i set it the other day....still exactly where i left it...midway the recommendation of 350 to 380mv...
dbt bright then dim as expected....
meters lit....no response from needles upon relay engage...nor disengage
after the testing...i rechecked all fuses....they are fine...
i did NOT reinstall the legs i removed to confirm the bad emitter resistors and r1 and r3....

Good job reporting, Might want to check the Bias Pot

 

[Gepetto]

ok...as instructed....

both 10 ohm resistors are good....both 150 ohm resistors are good on left back plane
no inputs connected....no speaker outputs connected....
right channel is fully populated with the new transistors i just got from joe....left channel transistors checked and rechecked...4 were bad...tossed
left channel has the bottom row populated only....2 checked transistors in the bottom row on the left channel....i checked 95/96 location...all is correct...with them alternating with 96 closest to the transformer....
all fuses good 2 on back plane 2 on chassis on left side...and the main ac fuse also good...
dcprotect relay engaged....i watched the reeds....and the blue led lit after a few seconds...i watched the relay disengage when i powered down...and the blue led went out...
the relay is not welded....it is functioning properly....
b+ is +82.4 and b- is -82.4 on the back planes test points...both sides
+- 15v test points on control board are +- 15v...both sides
the left bias is 13 to 14 mv and does not respond to bias adjustment...
right bias is 365...as i set it the other day....still exactly where i left it...midway the recommendation of 350 to 380mv...
dbt bright then dim as expected....
meters lit....no response from needles upon relay engage...nor disengage
after the testing...i rechecked all fuses....they are fine...
i did NOT reinstall the legs i removed to confirm the bad emitter resistors and r1 and r3....

BUMP...

You will get very low bias readings if you do not install the bottom row of transistors. Have you installed the bottom row?

If no, install them and recheck.

If yes, measure the voltage at the collector and emitter of the bias transistor at the control board connection points with your DVM black lead connected to the single point ground.

 

[gene french]

BUMP...

You will get very low bias readings if you do not install the bottom row of transistors. Have you installed the bottom row?

If no, install them and recheck.

If yes, measure the voltage at the collector and emitter of the bias transistor at the control board connection points with your DVM black lead connected to the single point ground.

yes sir...

 

[gene french]

yes sir...

i am trying to be thorough and careful....i will get there...

 

[Gepetto]

Remember the DBT is your friend...do not skip it.

 

[mlucitt]

Joe, a lot of my friends are dim bulbs. Is that what you mean...?

 

[Gepetto]

Joe, a lot of my friends are dim bulbs. Is that what you mean...?

 

[gene french]

i ALWAYS have the dbtester in circuit...
results...
with the left bias control set to min...
c= +1.05
e= -1.05
with the right bias set to 365mv
c= +1.46
e= -1.46
just in case you wanted me to test that side too...
maybe i wont need another bump...
naaahhh....
i will need it...

 

[gene french]

and again....this is with the right side fully populated...
and two transistors completing the bottom row....on the left side

 

[Gepetto]

i ALWAYS have the dbtester in circuit...
results...
with the left bias control set to min...
c= +1.05
e= -1.05
with the right bias set to 365mv
c= +1.46
e= -1.46
just in case you wanted me to test that side too...
maybe i wont need another bump...
naaahhh....
i will need it...

BUMP...

And how about with the pot set to max?

 

[gene french]

crap....i did not think of that....
ok...

 

[gene french]

no change....+-1.05

 

[gene french]

i am touching the screws on the phoenix bias connectors btw...on the back of the control board....just to be sure i am where you want me...

 

[Gepetto]

i am touching the screws on the phoenix bias connectors btw...on the back of the control board....just to be sure i am where you want me...

yes, did not know you had the board swung down or not

 

[Gepetto]

Well, knowing what you did to the amp and blowing open all those emitter resistors, my next spot to look is did you fry the protection circuit in the process of taking out those outputs and emitter resistors. The likelihood is high.

So I would next lift the anode end of D13L and the cathode end of D14L and recheck the bias range when adjusting the pot.

 

[gene french]

check the range by reading c/e voltages or reading bias from bias test point and speaker out

 

[Gepetto]

check the range by reading c/e voltages or reading bias from bias test point and speaker out

C-E readings would be preferable.

 

[gene french]

never mind...bias is adjustable now...
checking control point test point and white speaker post...set to 365mv

 

[Gepetto]

never mind...bias is adjustable now...
checking control point test point and white speaker post...set to 365mv

Hopefully this was valuable in learning how to debug. Now you have to trace down which of the limiting transistors you fried, or both...the MPS651 and MPS751. They are rugged transistors, but not that rugged.