Onkyo A 8450 Vollverstärker

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CarlM.
Inventar

#101 erstellt: 06. Jul 2025, 20:54

Look into #11, where Johannes postet his optimized schematics:

http://www.hifi-foru...-marked_1245973.html

It is not 100% identical but very close to it. It offers a good orientation.
Remember: in most cases the difference of potentials between emitter and basis must be about 0,6V ...
NPN B>E
PNP B<E

[Beitrag von CarlM. am 06. Jul 2025, 20:56 bearbeitet]

gemaux
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#102 erstellt: 06. Jul 2025, 21:27

Thanks for your help.
I'll check all that again but I suspect D 509 D511 which light up little

Best regards

gemaux
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#103 erstellt: 08. Jul 2025, 14:39

Hello

Between B and E (B - and E+) I find :
Q515 : -0,644V
Q511 : +0,786V Q512 : 0,704V
Q513 : +0,665V
Q601 : -0,516V
Q603 : +0,569V

D505 lights up a little and lights down after a second

D505 : +1,35V D506 : +0,637V
D507 : +0,2V
D509 : +0,54V D510 : +0,577V
D511 : +1,78V D512 : +1,73V

I suspect D505 D511 and D512 (?)
What do you think ? Should I change them?
LTZ R15 are difficult to find . Which ones may I change them with?

Regards

[Beitrag von gemaux am 08. Jul 2025, 14:46 bearbeitet]

CarlM.
Inventar

#104 erstellt: 08. Jul 2025, 21:54

Here you find the datasheet:

https://datasheet4u.com/pdf-down/L/T/Z/LTZ-R15_Rohm.pdf

All the LTZ-R15 should produce a difference between 1,70 to 2,30V.

Max. forward voltage of 1SS133 is about 1,2V (see datasheet for values depending on current) .

https://mm.digikey.c...s/docus/9/1ss133.pdf

Suspect: D507

p.s.
if you are not sure:
desolder and test outside the circuit.

[Beitrag von CarlM. am 08. Jul 2025, 22:20 bearbeitet]

gemaux
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#105 erstellt: 14. Jul 2025, 12:52

Hello
I have 1,47V between anode D505 and cathode D507 (0,76V between D 506/D508)
and 2,3V between anode D509 and cathode D511 (2,28V between D510/D512)
R527 : 46,8 kohms.

The values seams to be good when I measure separately from the board

D505,D507 and Q511,Q513,Q515 will be replaced
I already changed Q517.

And I hope it will be the solution .....

Regards

CarlM.
Inventar

#106 erstellt: 14. Jul 2025, 22:39

Don't forget:
There's a feedback line from the output to the first stage (differential amp).
Therefore a fault will cause anormal values all over the complete circuit.

If the actual focussed stage is okay I would seach the faulty part in the first stages.

In some cases I unsolder all of the transistors to check them unconnected. Then it is possible as well to proof theother parts on the pcb.

Good luck!

[Beitrag von CarlM. am 14. Jul 2025, 22:40 bearbeitet]

gemaux
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#107 erstellt: 16. Jul 2025, 16:37

OK
I checked separately Q503 Q505 Q507 Q509 .They are good.
When I remove only one of them the lamps light on .

The lamp lights off and the relay switches only when I remove Q515 alone.....

I have a doubt : On what reference point are the voltages indicated on the diagram measured? ground?
Ex :-48,8V on B of Q515
I find strange measures.

Maybe a short circuit as well

Thank you again..
Regards

CarlM.
Inventar

#108 erstellt: 16. Jul 2025, 19:46

gemaux (Beitrag #107) schrieb:

On what reference point are the voltages indicated on the diagram measured? ground?

Yes. I always fix the black cable (= COM) of the multimeter to the metal of the chassis. Then I can focus on the red cable (= 0..200 VDC).

The lamp lights on in two cases:
- shortcut
- the bias is not limited (faulty bias circuit)

[Beitrag von CarlM. am 16. Jul 2025, 19:49 bearbeitet]

gemaux
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#109 erstellt: 19. Jul 2025, 10:30

Hello

I finally found a short circuit .....
C of Q517 was not isolated from the heatsink.....I had replaced the original one with a equivalent and did not notice this difference ....
Bad mistake
Everithing works fine now .
Many thanks for your help and patience

CarlM.
Inventar