Pioneer SA-9800 with stuck meters

[whatisnext]

Hi All,

I have a Pioneer SA-9800 with power meters that are stuck. The top shows the meter at full power. The bottom meter shows 2-bars. They stay at these fixed positions no matter what volume I have it set to.

The dimmer and source selection are working properly. My tech is stumped and has replaced the Toshiba TA-7318P IC. Has anybody had this issue before?

Thanks for your help!

 

[Bryan Farmer]

Just curious does the meteor go back down when the speaker selector switch is selected to the off position.

 

[Bryan Farmer]

Disregard that last post as it would still be sending signal to the op amp with speaker selector in any position.

 

[whatisnext]

Thanks, Bryan. I tried it just to be sure and the meters are still stuck when in the off position.

 

[Hyperion]

Power meters reading with no output could suggest 'DC offset' present on the power amp output, have you checked this? I am assuming the unit powers up ok and isn't in protection mode. (check the supplies to the display section, make sure the voltages are in spec')
The only other cause that I can think of is a logic fault with the meter driver(s), but you say you have changed the TA-7318. There must be something (a ladder of diodes or transistors?) in between that driver chip and the fluorescent display to enable it to work - the answer may lie there.

Not a Pioneer expert by any means, and I haven't referred to a schematic in giving my input.

 

[rcs16]

I agree check out the power supply voltages first as with most repairs
Do the segments for indicating the function or tape monitor work properly?
You can test the ta 7318 in circuit. It provides a dcv relative to the Ac coupled signal at its input.
Possible that it is the ha12010 as well.

 

[whatisnext]

Thanks, all. I have no experience with testing circuits and will have to pay my tech to do the work.

The HA12010 was also replaced. I’m guessing that one of those ICs is defective. I’ll see if I can find OEM ICs. My suspicion is that a TA7318 that was sourced on the auction site is the issue.

 

[whatisnext]

Everything on the display works as expected. The Integrated Amp puts our wonderful sound without going into protection mode.