Aleph 30 problem - half of power supply voltage on speakers output

[aparatusonitus]

Measure Vbe (voltage between base and emitter) of ZTXs, not the base voltage per se, although it won't hurt.

[MEGA-amp]

also check that you have 4-5v between E-C at Q4

[yoke]

O.K.
top view ( o represents pins )

Q5 o 4.62V o
3.9V o 0.64V

Q4 o 5V o
4V o 0.6V


not shure but this should be like when woching from component side

c e
b


whell it looks diferent when I post, so if I'm right bouth have around 0.6V betwin b and e, and 5 or 4.6 be twin c and e.

[Zen Mod]

yoke , it's useless ( at least to me ) to post without known nomenclature ;

use this schematic , and just disregard part names on pcb ;

I know ( and have in my PC ) too much Aleph schematics , to even remotely be sure what you're talking about , without exact schematic ...

I hope it will help

[yoke]

Originally posted by Zen Mod
yoke , it's useless ( at least to me ) to post without known nomenclature ;

use this schematic , and just disregard part names on pcb ;

I know ( and have in my PC ) too much Aleph schematics , to even remotely be sure what you're talking about , without exact schematic ...

I hope it will help

you are rigth
there are several schematic of Aleph30 with diferent markings...
and it's been a while since I build this ;-)


lets resume
power is +/-22V

I have around 13V on the output
R11 - 5V
R14 - 2,5V
Z5 - 9V
Q5 - from c to e 4.6V from b to e 0.6V
Q4 - from c to e 5V from b to e 0.6V
Q 6-8 source resistors 0.5V
Q 9-11 source resistors 1V

[Zen Mod]

something is wrong

you can't have in same time 2V5 across R14 , and 5V across c-e of Q4

what value of source resistors you have , and how many output pairs ?

[yoke]

you are right - I have problems indetifaing resistors but voiltage is 5V on ztx

I have 2 x 3mosfets (just like original) and source resistors are 0.5Ohm

[Zen Mod]

in my xperience ( lifetime as repair techie ....... lousy one ) - fastest and most convenient way of repair - for simple circs as A30 is - is simply to pull out ( ONE BY ONE , to ensure possible mixing ) all semis

desolder it , pull out , measure
if good - solder it back , if suspicious - replace , if broken - replace


check input LTP ( both IRF9610) , for start ;

what WAS initial current through outputs - when you made amps ?

to me - seems that even 0V5 across each source resistor is on highish side ...... not to mention 1V ..........

[yoke]

Yes it seams that would do the trick...resolder everything...

The thing is that I can't keep amp on for a more than a fiew sec since the side with 1V on source resistors start to smell ;-)

so I have to turn it on and off...

About voltage on source resistors, 0.5V is normal....I think it drops to 0.45 once the amp heat's up. I think that this 0.25V on original shematic is wrong. It should be like 0.5V.

1V is to much and I have to find out what is cosing it.

will try to mesure some voltage over input pair of mosfets.