Pioneer VSX-1021-k volume decreases 3db every few minutes

[culcuhain]

Good afternoon!
I have a Pioneer VSX-1021-k that the volume lowers 3db every few minutes until it reaches -80db then it goes ---.

I have no voltage across the inducer when it auto drops but I do when I manually move the volume knob. I have deoxited it too with no changes.

Any suggestions on the next steps? I do have the service manual. No errors displayed and none in memory. Have done both soft and factory resets.

[madan1]

Re: Pioneer VSX-1021-k volume decreases 3db every few minutes

factory reset?

[culcuhain]

Re: Pioneer VSX-1021-k volume decreases 3db every few minutes

Yup. Done both soft and factory reset (multiple times).

[madan1]

Re: Pioneer VSX-1021-k volume decreases 3db every few minutes

Oops sorry, did not see that on my phone.
I just reviewed the service manual and damn... that unit is a nightmare to diagnose!
So... BD3473KS2 is the switching and volume control chip. It gets its control data on pin 11 - VLSO.
I traced VLSO through CN2202 (3) -> CN2108 (3) -> cn1502 -> connt_emma which seems to be going to IC101 UPD61283F1-407LU2A-K.

On the other end - s3024 is the rotary knob. It uses volA and volB to transfer data. The volume control data goes to pins 33 and 34 on "event ucom ic3004 lc87f5nc8a-e" ( pg73 ). This is a microcontroller which then communicates with the rest of the system and I guess the volume data goes in the datastream with the rest of the front panel functionality.

Since you do not see any other artificats, I would focus my attention on the rotary knob and its connection to the microcontroller.


By the way, have you tried to update the firmware?

[culcuhain]

Re: Pioneer VSX-1021-k volume decreases 3db every few minutes

thank you. Finally saw it in the service manual on page 32. The 2nd issue from the bottom. Overheat detection. Process after Detection, 3db down. TEMP L (TR DET) pin 81 on IC3004. Time to do some more digging.

[madan1]

Re: Pioneer VSX-1021-k volume decreases 3db every few minutes

Hmm shouldn't bad temperatures throw errors?
Anyway, check all connectors and then check the temperature sensor(s).. that's the easiest thing to start with.
See also if there's system menu that shows the sensor readings.

[culcuhain]

Re: Pioneer VSX-1021-k volume decreases 3db every few minutes

If the AMP overheats it throws an error. I think this is it's way of preventing it from overheating. Time to go through the schematics to find where the thermistors (@$$uming) are found.... This is a fun project.

[culcuhain]

Re: Pioneer VSX-1021-k volume decreases 3db every few minutes

Ok. Thermistors are SMD (1.6mm X 0.8mm) on the AMP7 board and one per channel. Looks like a channel is getting ready to short out....Will test tonight when I get home from work....

[culcuhain]

Re: Pioneer VSX-1021-k volume decreases 3db every few minutes

Thermistors checked fine. Looks like someone has been in this board before. Finger prints of thermal paste and gnarled heads on transistors. The dig gets deeper.

[culcuhain]

Re: Pioneer VSX-1021-k volume decreases 3db every few minutes

Pics of potential previous work. Gnarled Philips head slot and thermal paste finger prints...

[culcuhain]

Re: Pioneer VSX-1021-k volume decreases 3db every few minutes

Ok. Unscrewed the ones that looked to have been tampered with. Applied the correct amount of thermal paste and snugged it all back up. No change. Still dropping the volume 3db every 2 minutes. So I have a thermal issue. I rigged up a fan and then had it blow all over the board.... Same issue. volume still drops. My hand says no excessive heat coming from anywhere.

Next steps are:
1. put a stronger fan to confirm thermal issue
2. double check the thermistors
3. compare resistance in all thermistor circuit for abnormal resistance
4. replace thermistors
5. Replace Transistors
6. Pull hair out.

[budm]

Re: Pioneer VSX-1021-k volume decreases 3db every few minutes

Can you please upload the service manual?

[madan1]

Re: Pioneer VSX-1021-k volume decreases 3db every few minutes

here they are




p.s. page 33 -> front assy board -> ic3004 ( event ucom ) pins 81 and 72
normal readings should be 5V

connect that pins to 5V and see if it will continue dropping the volume. Meanwhile do not forget to check if any of the channels is overheating

[culcuhain]

Re: Pioneer VSX-1021-k volume decreases 3db every few minutes

Will check those voltages tomorrow.

[budm]

Re: Pioneer VSX-1021-k volume decreases 3db every few minutes

TR_DET:
In normal operation Q531 is OFF so the Collector Voltage will be around 5V, when temperature goes up, the PTC R406 resistance will go up which will bias on Q403 which in turn will bias on Q531 which will cause the Collector Voltage to go low.
So I would check the DCV of Q531 to see if it low or not. You can also cool down PTC using canned air duster upside down to see if it will cause the Collector Voltage of Q531 to go up.
I would not connect 5V directly to anything without using resistor to limit the current in case you slip up or connect that 5V to the wrong point such GND and damge the 5V supply or to the Collector of the Transistor that is in Saturation condition (fully on) which then the Transistor will be damaged.

[madan1]

Re: Pioneer VSX-1021-k volume decreases 3db every few minutes

If I remember right the front pcb is connected with a ribbon cable.... probably before everything else I would thoroughly inspect that ribbon cable. I've had a cable which had lost few connection pads in the end and other one with broken wire in the middle.

[culcuhain]

Re: Pioneer VSX-1021-k volume decreases 3db every few minutes

The collector on Q531 shows 0.07 VDC and volume drops. So it sounds like I need to check Q403 and R406, correct? Sorry about the delay in respond. Life got in the way.

[culcuhain]

Re: Pioneer VSX-1021-k volume decreases 3db every few minutes

Looks like there is a PTC for each channel.... New OEM AMP7 board $100.... so... I get to play with a dead board later. I appreciate everyone's help. Will update when it arrives.

[culcuhain]

Re: Pioneer VSX-1021-k volume decreases 3db every few minutes

Parts are backordered with anticipated delivery date of Mid June. Will update everyone then.

[culcuhain]

Re: Pioneer VSX-1021-k volume decreases 3db every few minutes

and back ordered parts are NLA from the manufacturer... Looks like I am back to checking the AMP7 board again. Sounds like a good Father's day project!