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SX-650 recap questions

J

jboerger3

Member
I started a recap job on an SX-650 given to me by my big brother a year ago. It is the version that has IC's in the phono section. The cabinet is in rough shape, but the faceplate is clean and it has all the knobs. This receiver has been worked on before. The power switch had been bypassed with a switch mounted through the top of the cabinet (not where I would put it). I put it on the dim bulb, checked it for DC on the speakers before trying it out. I deoxed the volume and balance pots. Both channels work, but they are noisy. Thankful that the power packs work. If they didn't, I would have stopped there.

I replaced all the caps and transistors on amp board 1 (GWH-101) without issue. I did not replace the 2SA798's - yet. I guess I should at least remove them and test? I do have (4) 992's that match pretty well if I need to replace the 798's. GWR_101 was pretty dirty on the foil side (see Pic). It appears to be a white powder residue. Anybody have any ideas? I sprayed with 91% IPA, but I need to get out the q-tips and wipe it down.

I replaced C23, 24, 28, and 29. All of the caps on the amp boards appear to be OEM as they are all the light blue Nichicons. When I pulled C36 it was a 100uf 16v. The service manual documents it as a 220uf 16v. I don't understand schematics enough to know if the circuit around Q14 and Q15 should have a 220uf or a 100uf. And I don't know if C36 had been replaced. Has anyone run into this on an SX-650?

Lastly, Q5 and Q6 appear to be matched as they have yellow paint on top (see pic 2). The schematic doesn't present them as a normal differential pair. But, should I match any replacements? Pic 2 also shows the empty space for C36.

I appreciate all the help that I received when I recapped my SX-950 a couple years ago (still sounds great) and also the SX-434 that I finished a couple of months ago.
 

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I'm not familiar with the SX-650, but on numerous occasions I've found a cap in a Pioneer unit that doesn't match what the SM shows. If you're fairly certain the cap in the unit is original it's best to use that same value - not what the SM shows. Pioneer didn't update their SM's for design updates during their production runs, and unfortunately it appears they didn't produce any other documentation listing those design changes (at least nothing that's still available today).
 
Thanks for your response Shakira. I am aware of undocumented changes mid-production. There were three versions of the phono stage during the production run of the SX-650. I was hoping that someone could say that my version (likely the last version), with the 2 IC's, had the change to C36. I saw another SX-650 post, with a picture of a 220uf cap in C36. Unfortunately, my unit doesn't sound right and I don't know if whoever worked on it in the past made a change or not.
 
I checked my notes on a SX-650 I restored last year and yep, C36 on PCB GWR-101 was a 100uF/16V contrary to the 200uF specified in the SM.
 
As for the transistors, Q5 and Q6 were 2SC1649. To my knowledge these are not known to be troublemakers. The 2SA798 however are problematic and recommended to be replaced. Matched pairs of KSA992 will work as you noted.
 
Thank you Ray66. Did your SX-650 have ic's in the phono section? I am curious about when during the production run this change was made.
 
Do you have a scope? If so, you can trace the signal from the function switch to the outputs to see where the noise starts. Once you have identified where the noise starts in the signal path you can start checking components.
 
jboerger3 said:
Thank you Ray66. Did your SX-650 have ic's in the phono section? I am curious about when during the production run this change was made.
Click to expand...
Yes @jboerger3, mine had a pair of 7-pin SIP (single inline package) ICs located near the phono inputs located at the rear of Tuner/AF Assy AWE-075 PCB. You are correct, the SM does reference earlier versions that had a separate phono PCB (Equalizer Amp Assy AWK-065).
 
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