Replacement filter caps for SX-3900

[Raccoon1400]

Mark:

I'm thinking I will revisit this one. I'd like to think I've learned a few things since I last tackled it.

Previously, we found pin 4 voltage on the driver board was way too low. Yet protection was engaging. Then it blew up for no apparent reason. This may have been because I broke a lead on one of the STV diodes. I replaced the blown outputs with ones from a parts 3800. But I saw a post that says you haven't had luck doing that, due to the parts not being matched.

So I'm thinking I'll shotgun the driver board and replace the outputs with new parts you suggested. Do you have an up to date parts list? I found a old list of yours but some parts are NLA. (See link in post #37)

 

[markthefixer]

That is NOT the correct parts list. NLA parts are only the tip of the iceberg. Speed and distortion problems with the to-220's and other stuff happened. You do NOT want to use that list.
iirc, these were used, but the mix is a bit counter-intuitive...
512-KSA992FBU (ln)to-92 ecb 120v .05a .5w 100mhz 300-600hfe $0.17 ea
512-KSC1845FTA (ln)to-92 ecb 120v .05a .5w 100mhz 300-600hfe $0.05 ea

512-KSA1220AYS to-126 ecb 120/a160 1.2a 1.2w/20w 175mhz 35-320hfe $0.39 (R=60-120, O=100/200, Y=160/320)
512-KSC2690AYS to-126 ecb 120/a160 1.2a 1.2w/20w 175mhz 35-320hfe $0.40

757-2SA1930(Q,M) pnp to-220 bce 180v 2a 20w 200mhz 50-320hfe 200mhz nsa driver
757-2SC5171(Q,M) npn to-220 bce 180v 2a 20w 200mhz 50-320hfe 200mhz nsa driver

and for outputs, I don't remember if they were:
863-MJL1302AG pnp TO-264 bce 250V 15/30A 200W 30mhz 45-150hfe $3.57 ea
863-MJL3281AG npn TO-264 bce 250V 15/30A 200W 30mhz 45-150hfe $3.57 ea
OR
863-njw1302g pnp TO-3P bce 250V 15/30A 200W 30mhz 45-150hfe 2.55
863-njw3281g npn TO-3P bce 250V 15/30A 200W 30mhz 45-150hfe 2.32

and a few others...




This thread: Pioneer SX-3900 - Idle current too high we are currently dealing with the ramifications.

Watch that thread for a while, and somehow, sometime, the parts list will be updated or posted. I already checked my electronic notes, and it's not there, so it has to be in my paper notes, because I have successfully done several of these (3900/d7000) amp boards. So it's going to be an archeology expedition through a mound of paper - on top of EVERYTHING else I have to do.

 

[bktheking]

I ended up buying this 3900 from Raccoon and fixed the hum issue yesterday. I want to post the fix in case someone else runs into this issue- i'm guessing this would apply to any of the receivers in this series. The solve- as mentioned by Raccoon, the previous owner had been in the unit prior and had done some repair work. There are 2 black ground wires going to pin 6 and 7 of the amplifier board. I was checking grounds, when I grounded pin 3 of the PS board the hum got cut in half- that's odd i thought. So i followed the schematic grounds and discovered the previous owner had reversed the grounds. Once I swapped them around the hum is now gone.

Cheers

 

[markthefixer]

I ended up buying this 3900 from Raccoon and fixed the hum issue yesterday. I want to post the fix in case someone else runs into this issue- i'm guessing this would apply to any of the receivers in this series. The solve- as mentioned by Raccoon, the previous owner had been in the unit prior and had done some repair work. There are 2 black ground wires going to pin 6 and 7 of the amplifier board. I was checking grounds, when I grounded pin 3 of the PS board the hum got cut in half- that's odd i thought. So i followed the schematic grounds and discovered the previous owner had reversed the grounds. Once I swapped them around the hum is now gone.

Cheers

Thank you for the follow up.

That makes sense.
The pin 6 ground is a current return path (pin 3 awr-210) and reference from the protection circuits back to the power supply, and they are purposefully isolated from the amplifier.
The pin 7 ground is a signal ground reference and slight (quiet!) very low current return (pin 21 awr-210) from the input stage of the channels.

on the power supply board there DELIBERATELY is no connecting foil between pin 3 and pin 21.
A power return ground can constantly vary a bit due to the current flowing interacting with the resistance of the ground path. If there's AC current on that - you hear hum.

Imagine the nightmare of hum between the grounded center tap of a transformer secondary and the main storage capacitors.

That is why grounds are not confused, or interchangeable.