Onkyo TX-4500: distortion driving me nuts

[Bert Beukema]

Here is a scan of the basic adjustments:

The service manual is incorrect in this regard, those setup terminals do not exist on the 4500 MK1
I am checking my previous repair notes on this.

BB

 

[Bert Beukema]

Yes, but requires a signal gen. and O'scope, I think.

Signal generator is't an issue but my scope is in repair with a scope specialist until next week.
Hope to get this thing done before that time.

BB

 

[Bert Beukema]

So finaly done. For those struggling with the center voltage and idling current:
This is for the left channel. Right channel is the same procedure. Just change where it says 5 for 6,
So R536 (left) = R636 (right).

CENTER VOLTAGE
---------------------------
Add a speaker or an 8ohm 50w resistor.
Connect multimeter; black = earth and red = SP terminal. (SP left side)
Set trimpot R504 to 20mv (+/- 5mv).

IDLING CURRENT
---------------------------

Connect mutlimeter across R526 (orientation does not matter).
Set trimpot R518 to 20mv (+/- 5mv).

That's it, good luck!

Again many thanks for all your help, without it I would have been stuck in purgatory forever .

BB

 

[gadget73]

so what was the problem, just incorrect adjustment or was there actually something wrong ?

 

[Bert Beukema]

so what was the problem, just incorrect adjustment or was there actually something wrong ?

A somewhat hidden 2W resistor was high ohms (in the millions).
Despite checking the board over multiple times that one I constantly missed.
But the remarks here prompted me to desolder all resistors and recheck them out of circuit.

BB

 

[gadget73]

aha. I've found stuff like that before, things that seem to measure OK in circuit but out of circuit are junk. Have been mislead by that more than once.

 

[Bert Beukema]

Yup, another example why testing out of circuit is the smart move.
Especially when an apocalypse happened to your circuit.
But always in a hurry and so much work to do. So I cut corners in this case.
Lesson learned (again) .

 

[janjaap]

Hallo, ik zoek Bert Beukema, student electrotechniek vanaf 1974 aan TU Twente. We organiseren een reunie voor de Witbreuksweg. Je kan mij vinden op Linkedin.