• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

Pioneer SX-980 Stereo Indicator Lamp Failure

Z

zatchison

New Member
Hello all, hope I'm posting this in the right forum as this is my first thread.

Service Manual
I have a SX-980 that is working in all but one area, the Stereo Indicator lamp. From what I know, it is either the lamp or the MPX Decoder. I'm having trouble locating the MPX Decoder for further troubleshooting by using the manual. I'm not sure what to proceed with next here for this repair, should I replace the lamp first or rule out the MPX?

Would love some advice, thanks.
 
Register to hide this ad
One side of the stereo lamp is connected to plus 13 volts
The other side of the stereo lamp is connected to pin 15 of the AWE-094 tuner board.
There is a 160 ohm Resistor R37 connected between pin 15 and Q6 PA1001-A pin 6 the MPX Decoder integrated circuit.

When there is no stereo signal the stereo decoder, Q6's PA1001-A pin 6 sits off (not conducting to ground),
with pin 6 resting at plus 13 volts when the lamp is good, and far less if the lamp is damaged.

When a stereo signal turns on the stereo decoder, Q6 PA1001-A pin 6 turns on and conducts to ground, allowing current to flow to ground which lights the lamp.

WARNING,
too much current flowing through Q6 PA1001-A pin 6 will hurt Q6.
the resistance of the lamp is counted on to control the current.
Also changing to a LED means adding an extra, and significant resistance to the circuit.

the stereo lamp is an 8 volt 50 milliamp lamp, R37 saves Q6 when an 8v, 35 milliamp lamp is used in that 13v circuit.
shorting the 8v lamp will destroy Q6.
 
Last edited:
markthefixer said:
One side of the stereo lamp is connected to plus 13 volts
The other side of the stereo lamp is connected to pin 15 of the AWE-094 tuner board.
There is a 160 ohm Resistor R37 connected between pin 15 and Q6 PA1001-A pin 6 the MPX Decoder integrated circuit.

When there is no stereo signal the stereo decoder, Q6's PA1001-A pin 6 sits off (not conducting to ground),
with pin 6 resting at plus 13 volts when the lamp is good, and far less if the lamp is damaged.

When a stereo signal turns on the stereo decoder, Q6 PA1001-A pin 6 turns on and conducts to ground, allowing current to flow to ground which lights the lamp.

WARNING,
too much current flowing through Q6 PA1001-A pin 6 will hurt Q6.
the resistance of the lamp is counted on to control the current.
Also changing to a LED means adding an extra, and significant resistance to the circuit.

the stereo lamp is an 8 volt 50 milliamp lamp, R37 saves Q6 when an 8v, 35 milliamp lamp is used in that 13v circuit.
shorting the 8v lamp will destroy Q6.
Click to expand...
Mark, in your vast experience is it more likely to be a lamp issue or MPX issue?
 
Lamp
listen to FM stereo with headphones, toggle on and off MONO, if good you will unmistakably hear the difference.
We don't need no steenkin lamp !!!
 
You must log in or register to reply here.
Back
Top Bottom