Onkyo TX-8500 mkII digital tuner indication.

[anderslober]

Meter is out again.......I need to desolder the protective shield.....then the new crystal will go in......

 

[anderslober]

Sorry to say guys.......with new crystal.....still stuck at 186.8Mhz....:-(

Any other ideas? Time to change the other IC's?

Which IC actually controls the displayed numbers correlated with the tuning needle?
Could the meter be defective? In the upper right hand corner...it does have a black spot...........

 

[anderslober]

I ordered new IC's.......HD7940 and HD74s112p........will try them too......

Now I just have to wait......2-4 weeks.....horrendously slow shipping........

 

[Binkman]

make sure ground from pcb to chassis grounds on are good. Display chip?

if plays audio? aux? use external tuner if new chips don't work. wouldn't get 5$ in usa anyway. your talents better used for better stuff perhaps?:yes:

 

[sregor]

make sure ground from pcb to chassis grounds on are good. Display chip?

if plays audio? aux? use external tuner if new chips don't work. wouldn't get 5$ in usa anyway. your talents better used for better stuff perhaps?:yes:

Tuner is analog, so chip only affects display. My 2 cents

 

[c.coyle]

Could this be a mechanical problem? Have you visually inspected and physically manipulated all foils, leads, solder joints, display pins, and grounds? Nearby discrete components? Re-flowed solder joints? Checked for shorts?

EDIT: Just so I'm 100% clear, is it actually tuning from station to station?

 

[anderslober]

Yes......it tunes fine. All stations come in with stereo light an'all. The display is stuck at 186.8mhz.........
It has worked before........that is for sure. When it stopped working, we had just had a storm and a power cut/surge.....I guess this affected the display.

I would really like it to work......so, I have ordered the chips....will put 'em in and see what happens.

I have inspected grounds, solder connections, etc.....all seem good. Therearen't many wires going to the display anyway......

 

[c.coyle]

. . .When it stopped working, we had just had a storm and a power cut/surge.....I guess this affected the display. . . .

Well, that's sure a possibility. The display itself might have been fried. Have you checked any voltages on the chips or display against the manual or schematic?

 

[Binkman]

could be a counter chip. have similar onkyo analog and perhaps another chip.. just saying if amp works.

 

[sregor]

Do you have access to an oscilloscope? Try troubleshooting. You should be able to see the oscillation of the crystal chip, and signal from the prescaler chips. If scope and probe are 100mHz, you can follow signal from local oscillator to counter.

 

[anderslober]

No scope.....yet! I am also trying to find a display.....will change that too, if I find one. Do any other models use the same display?

 

[bktheking]

Won't be the display, they either work or they don't. Focus on getting the replacement ic's.


Sent from my iPhone using Tapatalk

 

[anderslober]

Cool. Waiting for the IC's to arrive........

 

[anderslober]

I got the replacement IC's....popped them in.........ALL IC's and crystal are now new.....still no joy......display stuck at 186.8.......

What could this be? And where could in be? Is the fault on the display board? Or...?

Thanks.

 

[anderslober]

Here is a picture of the scat of the display board.....look at cap c714 and c711. Is that correctly depicted?

Shouldn't c711 have the '-' towards ground?

 

[petehall347]

those caps are both correct . one positive voltage going to + the other negative going to -
did you try changing c712 c713 yet ? if one or both of them has gone bad it may well affect the crystals operation .
on the scat i see osc in . i guess osc is oscillator .might the problem be in the oscillator rather than on the board shown ?

 

[anderslober]

Ok.....what do I test/change in the osc? Q721? If it is in the osc.....what could it be?

Caps on the display board are brand new......and double-checked.

 

[anderslober]

I found a japanese website where there was a bit of info on 2sc461 'outhouse' tr. As far as I could read, this tr can cause problems FM circuits..............q721 in the oscillator circuit is a 2sc461....

 

[petehall347]

hope i am right as it was only a wild guess .
i have never studied how these circuits work .

 

[anderslober]

Pete...I have been measuring voltages.......display board first......I have -5v where it should be +5v.......I have +7.9v where it should be -8v..........any ideas?

Also....on the tuner board where I should have -13v on -B.....I have +11.4v.........any ideas.........?

Maybe the scat is wrong......it happens...........