Pioneer SX-780 problems

[Jeff Harrell]

I see it on the schematic but locating it on the pcb is tough for me. I think I found R259, it had a canvas like cover over it. Apparently its gotten hot, when I peeled back the cover the paint came with it.

I cant get a good reading on it, it bounces from 0 - 285

 

[larryderouin]

These are the 2 white rectangular modules on the top side?

Yep. Should be 4 of them. Mine had the dual .22's.

 

[larryderouin]

To measure resistors in the 780, 1st UNPLUG IT, then De-Solder one end to get it out of circuit. This is why you are getting bouncy readings. Measure resistors only when powered down and best if one end out of circuit. Measure resistor. Write down result before you do anything else. If you aren't sureof the reading, measure again. BTDT, and with increasing regularity. Anyway. once you get the reading, if it's more than 10% out of spec, hi or low, replace it. 1/4w metal film is sufficient unless the manual specifies otherwise. Use the same value.

 

[Awesomeaudio]

Ok, I'll butt out Jeff.

 

[Jeff Harrell]

Thanks guys for putting up with my ignorance. I'll reply when I have an update

 

[Jeff Harrell]

After a little rest and some coffee... Can you provide a sanity check?

R259 has a green stripe it appears, the other colors are indistinguishable

 

[petehall347]

it should be red black brown 200 ohms ..
look at the same one on other channel to see .

 

[Jeff Harrell]

I know the schematic shows 200ohm but I cant see how these 2 resistors have those ratings. R259 and R260 aren't even the same, so I'm scratching my head. I'm fairly confident that I'm looking at the correct resistors. I've read another post here that said he had 150ohm resistors from the factory on this same model unit. I'm including a high-res photo of the area... R259 could be a 150ohm but its still hard to tell for sure.

Here's a link to the photo with notes. Could be a possible arcing near the cap, and 2 resistors with shields show evidence of heat
http://imgur.com/a/v7y3N
click to enlarge

Thanks!

 

[petehall347]

r260 has heat damage by the looks of it .
what do they measure with your meter ?

150 ohms brown green brown .

 

[Jeff Harrell]

Best I can tell with this meter...

R259 & R260 = ~152ohm

 

[petehall347]

might still be ok then , i would change anyway as its been stressed and might not work as well as it should and give up later .

 

[Jeff Harrell]

yea, i'll replace them. They'll be easy enough to acquire and install

I came here to post my parts list but its proving difficult to find parts:

4x .22ohm double emitter resistors everyone seems to recommend replacing them regardless (r265, r263, r266,r264) mouser # 588-TUW5JR20E out of stock any alternatives?
2x 2sc1775a for q11, q12 (Mouser Part #: 512-KSC1845FTA will work???)
2x 2sc1885 for q13, q14 (Mouser Part #: 512-KSC2383OTA will work???)

2x 200 ohm for r259,r260 1/4w, what is an acceptable tolerance?
2x 510k ohm for r257, r258 1/4w, what is an acceptable tolerance?


The power packs should arrive tomorrow, if installed and tested, could i damage them if any of the items above are at fault?

 

[petehall347]

yes damage may be caused if transistors have gone short circuit .

 

[Jeff Harrell]

I understand

Any suggestions on the parts I've listed above?

 

[Jeff Harrell]

after more reading, it appears that mouser 71-CP0003R2200JE14 may be suitable for replacing the emitter resistors.

Still unsure about the transistors and tolerances on the resistors

 

[Jeff Harrell]

Ok, I feel pretty good about these parts:
4x .22ohm double emitter resistors = mouser 71-CP0003R2200JE14
2x 150 ohm for r259,r260 1/2w, @ 10% tolerance (Schematic shows 200ohm but i see that many 780's shipped with this, as mine appears to have)
2x 510k ohm for r257, r258 1/4w, @ 5% tolerance

Still hunting replacements for these:
2x 2sc1775a for q11, q12
2x 2sc1885 for q13, q14

Edit: I've actually found the 2 transistors on ebay, guess i'll grab them to be safe

 

[rcs16]

You should do some searching
http://audiokarma.org/forums/index.php?threads/2sc1885-closest-replacement.616822/
EW suggests to use ksc2690A as a sub for 2sc1885 could also use KSC2316
ksc1845 is a sub for 2sc1775A
check/verify the pinouts

 

[Jeff Harrell]

You should do some searching
http://audiokarma.org/forums/index.php?threads/2sc1885-closest-replacement.616822/
EW suggests to use ksc2690A as a sub for 2sc1885 could also use KSC2316
ksc1845 is a sub for 2sc1775A
check/verify the pinouts

Yea, I guess I should have been more clear earlier. I did see those replacements but mouser doesn't carry them except in the variants I listed above, at least for the ksc1845. I wasn't sure if the added suffix to the part numbers were significant or not.

 

[larryderouin]

The 1st suffix # is the gain (also listed as hFe) and the rest are packaging type. Mouser lists these if you click on the pkg type. Also the datasheets are needed for these transistors as the pinout is most likely different from the originals. Mouser has them listed also in the pull down for ordering these. Stay off E-bay for transistors, unless they are NOT available @ mouser, digikey, newark, etc. Keep with the Known reliable distributor to ensure you are not getting a fake transistor.

 

[Jeff Harrell]

Thanks Larry for the explanation.
looks like mouser # 512-KSC2690AYS has the same pinout as the original 2sc1885
and so does 512-KSC1845FTA for the 2sc1775A