Repair Note: Pioneer SA-9100 Power-off Pop AWM-025C Protection Board

[merder]

Most SA-9100 schematics (all that I could find, anyway) show the AWM-025A board, mine has an AMW-025C with a resistor (R29) that doesn't appear on the AWM-025A board.The person who worked on this before me replaced R29, a 47k resistor per the AMW-062 schematic, with a 2.2k resistor. The result was -10v on the base of Q6, which caused the unit to make a popping sound when powered off.

The AWM-062 board layout does appear to be the same as the AWM-025C as far as I can tell... see the thread below:

https://audiokarma.org/forums/index.php?threads/sa-9100-protection-light-on-and-off.793948/

I realize this error was unlikely and specific to the unit I repaired, but hopefully the info will help someone. The only reason I can think that someone would have done what they did was that the A board schematic shows a 22 ohm resistor in a place where someone might be confused if they didn't realize they were looking at the foil side, but I have no idea. I am not a tech, by the way, I am a hobbyist, please correct/advise/add info if needed. If someone could link to the proper AWM-025C schematic that would be great.

 

[markthefixer]

the popping sound on power off is the loss of protection.

I do believe that if tested, the DC detect protect and the over current detect protect are not working

The R29 47k goes from the -13v supply into Q6 base. This is a delicate balance of currents and voltages controlling the operation of the Q6 protection trigger transistor, who's function is to discharge the timing capacitor and thus drop the protection relay connection between the amps and the speakers.
In other words: "trigger protect!!".

It was intended that the loss of the -13v should trigger the protect, just as if pin 12's 7.5vac signal was missing.
The Q3 & Q4 DC detector didn't fail into fault when loosing the -13v.
Other changes are R23 from 8.2k to 12k and R25 from 3.9k to 2.2k.

you can find an AWM-062 schematic and board layout as part of the SX-939 service manual.


In other words: if it pops on power-off, it's BUSTED!!!

 

[LesE]

AWM-025-C was also used in the SX-737 and SX-838.





SX-737 SM Hires