help to set dc offset to threshold s450

[Zen Mod]

offset is not good , but you have bigger problems if amp is not making music on output

yes , connect cap in series with speaker (to protect it from DC) and it must make music

if that's not the case , your amplifier needs proper repairs , which I'm afraid you are not capable of

so , make test again

just to make it clear - without proper repair procedure , you can't declare what's wrong - output transistors , front end , or both

 

[alfalf1]

yes confim it, with cup in serial to speaker not make music but spike like transistor burned.

but when i remove the cap the make music but i cannot increase he volume more

so the my consideration abut problems also in the output stage was valid.

is there just one output stransistor burned can it work in the manner indicated above ?

 

[Zen Mod]

no , you can't make assumptions like that

troubleshooting broken amplifier is complex process

I'm usually working backwards , from output stage - short circuit test for each element, diode test for each transistor , checking for shorted or damaged resistors etc.

without at least some experience in that , it's best to leave repair of such complex amp to someone who knows more - that way possible damage and final cost is always smaller

 

[alfalf1]

perhaps I have found the problem

hi Zen perhaps I have found the problem

i have dismount the output stage to check all 22 power transistor

and if i test whit the test in posistion test diode between the pont incicated B and EIi see an short circuit also if i change + and - tester tip, see folloging picture:

B shold be the base of transistor and

E shold be the emitter of transistor

but betwhen b end e i see an short

si i think the transitor is damaged confirm my idea ?

or i make an error ?

so it is true for all 20 thansistors indicated in the schemaindicated
q4 q6 q8 q10 q12 q14 q16 q18 q20 q22
and
q3 q5 q7 q9 q11 q13 q15 q17 q19 q21

i wait your answer

 

[Zen Mod]

all upper ones are in parallel , same as all lower ones

so , you can't be sure which one is shorted , without unmounting them from pcb

in fact , for B-E and C-E measurement you can , desoldering emiter resistor of transistor you're measuring , but for B-C measurement , you need to pull out one by one

 

[alfalf1]

ok thanks very much

 

[miguelnoda]

hello I have a Threshold 450e stage and it has two bad transistors and they have no reference anyone can help me

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