SX-828 Issue--wire on tone board came loose...

[EastPoint]

With headphones and the balance turned to the right, I get no sound. With the balance on the left, I get sound from just the left on the phones.

At first I got it on both sides of the phones, but the headphone adapter was bad. I tried a different one and it's just the left now.

 

[backinthelou]

Have you deoxited the switches?

 

[EastPoint]

Yes, pretty well. It was playing out of both channels just fine when I got it. Then I recapped the tone board and snapped that wire and it was down to one channel.

 

[backinthelou]

Make sure you didn't create a solder bridge anywhere.

 

[markthefixer]

Ok, next step:

So let's work BACKWARDS... The AF unit, AWK-012 that has the volume and balance controls on it, pins 1 and 2, do they have wires on them? white an pink pair?
pins 15 and 17, also a pink and white pair? Be SURE the wires aren't just held close, but actually connected.

Temporarily short pins 1 and 2 and see if the sound comes back
then do the same for pins 15 and 17.

We're looking for "the break in the chain"....

IF that does not bring out sound through both channels: on the AF unit AWK-012, did you just re-cap it or did you replace ANY transistors? If you did transistors, how did you determine the proper lead installations? Remember, there are 6 ways to install a transistor and only ONE works...

Of course it goes without saying to check for reversed capacitors and such other things.

 

[EastPoint]

I tried jumping 1 and 2 and no sound out of that channel. I tried jumping 15 and 17, still no sound. I did not replace any transistors or anything else--just the caps on that board.

 

[markthefixer]

It used to work before the recap? It is possible that neither are related, as long as all the caps went in correctly. A reversed cap looks like a short circuit.

wet your finger and touch pins 14 and 13 separately and see if there is hum you can hear, on each channel, one at a time...

If so, then do the same (touch) for the base leads of Q7 and Q8 (use the on-board symbol). If you can hear hum on one but not the other, that is a clue

IF you hear hum on both, then do the same (touch) for the bases of q5 and Q6.

If you can't get your finger in there you can take a wire or paperclip that you hold (and INSULATE all but the tiniest portion of the tip and also leave bare where you are holding it with moistened fingers to prevent shorts) and use that instead.

You could try it on the bases of q3 and q4 BUT I expect those to be the problem. They have a bad reputation. I ALWAYS replace them to eliminate call-backs.

 

[EastPoint]

Where are the Q5-Q8? Are they on the tone board, or a different one? I didn't see anything on the circuit board labelled with Q.

 

[markthefixer]

all this right now is the tone board. The q label is on the schematic and the foil side board layout diagram. It is what a transistor is called.

you need to work from the service manual, the foil side board layout diagram, looking at the pictures you posted, I can SEE the transistors.

The group of four close together is q1, q2, q3, q4, with q7, q8 further over and q5, q6 very close to the end of the board between pin 18 and the tone pots.

edit - this is a double sided board - perhaps without plate throughs between pads (copper conductor on the WALLS of the drilled hole!!) on opposite sides, or they could have been damaged when removing the capacitors for replacement. In that case the cap lead has to be soldered on both sides of the board to make contact.

Either way, the preceeding procedure will help localize the problem.

this might help:

Use the symbol silk screened onto the board.

every Mouser transistor has a data sheet available for download.... download them and look them up. then install as per the symbol printed on the pc board at that location.
never ever use the original transistor to determine how the replacement will go in.

from an earlier post:



First you need to learn about what the three transistor leads are about, and identifying which is which and where it goes according to the symbol. Then you will see that my parts list include lead arrangements - which assume the transistor lettering (and flat) are facing you and the leads are facing down, then go left to right.

Q13 2sc938 150v 0.05a 0.6w
512-KSC2383YTA to-92L ecb 160v 1a .9w 50mhz 160-320hfe $0.17

The big TO-220's with the metal mounting plate are hard to reverse, but the smaller ones are, but my specified replacements are usually E C B as a rule of thumb BUT we ALWAYS CHECK...

But you really should start here and follow ALL the links...

http://www.audiokarma.org/forums/showthread.php?t=331932&page=5

here's a preview, DO YOU SEE these symbols on the boards you are working on?:

e is always the arrow on one angled line (direction can be out (npn) or in (pnp) towards the base)
b is always the flat line the other two lines come out if at an angle
c is always the angled line without the arrow

letters can be smudged or illegible, while the symbols are hard to mistake and pretty language independent
pioneer doesn't use letters, if there is a symbol. sometimes in a linear hole arrangement, there is only an 'e'.... with no room for a symbol.

-----------------------------------------------------

now a quick lesson on installing a small transistor in a traditional triangular hole arrangement with a symbol printed in the center of the triangle

1. find the LEFTmost lead on the package and identify it's designation (emitter? base? collector?)
2. look at the symbol on the board, find the corresponding hole
3. insert that lead into that hole
4. find the RIGHTmost lead on the package and identify it's designation (emitter? base? collector?)
5. look at the symbol on the board, find the corresponding hole
6. insert that lead into that hole
7. the center lead will now need to bent forward or back to go into the leftover hole.

DON'T THINK "WHERE IS THE FLAT FACING"
think
"outside leads" and THEIR holes...

this one's ecb....

and two transistor layouts, ebc and ecb with the same triangular target hole arrangement

well, you do need to get the parts, first....

and when ordering the transistors, mouser has links to the transistor's data sheets, DOWNLOAD the data sheets!!! THEY are your BEST guide as to the correct lead connections for THAT particular transistor.

Do you understand the transistor symbol? enough to identify the emitter, base and collector from it? Because most boards (Pioneer) have the symbol printed on it, with holes around it, and it is orientated so there is an emitter hole, a base hole and a collector hole. And obviously, only the transistor's emitter goes into the emitter hole, the base into the base's hole and the collector into the collector's hole. IF you want it to work...

oh, and by the way, the symbol usually DOESN'T have the E, C and B letters ON on it... :stupid:
there are two flavors,
pnp: arrow pointing in, 2sa,2sb, ksa, ksb part number prefixes
npn: arrow pointing out, 2sc,2sd,ksc,ksd part number prefixes

hint: if "rotating" it in your mind is a puzzler, orient it in the hole this way(transistor hole arrangements are usually triangular):

choose the leftmost lead, use the data sheet to identify it... for example it is the emitter
put it in the emitter hole

choose the rightmost lead, use the data sheet to identify it... for example it is the base
find the base hole, rotate the transistor line of leads around the inserted leftmost lead to point at the base hole
put the rightmost (base) lead in the base hole.

the THIRD hole is now either in front of or behind the transistor, in this example the collector is "left over"
bend the center lead forward or back to go into the hole.

easy...

notice that this example had the lead order of emitter, collector, base which is a common lead arrangement

that means that:

looking at the transistor, with the leads pointing DOWN, and the flat part (or lettering in the case of some zetex transistors) FACING YOU
going from left to right has the lead order of emitter, collector, base

This is NOT your board, but it should convey the idea:

 

[EastPoint]

I tried with the pins 13 and 14 and I got a very very faint hum. I then tried with the 4 base pins you suggested. On two of them I got a nice loud hum, and on the other two I got huge pops, one of which put the receiver into protection for a minute.

While I was doing this, I looked at the cluster of 4 transistors (Q1-4). One of them was mashed down onto the board, and two of its legs were touching each other. How likely is it that this is the culprit? If I pull it, can I test it with a multimeter?

 

[markthefixer]

if mashed together, straighten it so the wires are not touching, then recheck for sound. It may have survived. Fingers crossed....

VERY likely that is it...

 

[EastPoint]

Yep, unbent them and still getting it on only the one channel. It looks like it's the 2SA725G. I saw a bunch of 2SA725 transistors on eBay--should I just grab those and replace both of them?

 

[markthefixer]

no no no no no......!!!!!!!!!

you haven't been in the Pioneer Audio Forum much, have you?

the 2sa725 transistors are replaced by the ksa992, and the 2sc1312 transistors are replaced by the ksc1845. Their pinouts are ECB.

512-KSA992FBU (ln)to-92 ecb 120v .05a .5w 100mhz 300-600hfe
512-KSC1845FTA (ln)to-92 ecb 120v .05a .5w 100mhz 300-600hfe

mouser.com.

There are other transistors as well, but since they aren't giving trouble and you are new to this, we'll let them be for now.
The phono amp for example takes 6 ksc1845's.

You SHOULD notice an improvement in the sound as well.

What (pre-existing) list did you use for the caps you used, please post a link to it. The transistors should be (put) in it.

 

[backinthelou]

Wow!! That's a lot of help you are offering Mark. Kudos, sir.

 

[markthefixer]

I've been doing that and more since 2005, 18 thousand plus posts with a majority of them more technically detailed and involved than that liddle un...

The whole thing about lists here - I instigated it, posted work I had to do during repairing many many units. Then it snowballed.

did you see this:Pioneer Recap Lists" Sticky suggestion! thread??

 

[EastPoint]

I swapped the transistor today but managed to snap the resistor next to it in the process. Orange orange orange gold is 33k, right? I ordered a batch of those and will get that swapped when it comes.

On another note, the large 330k resistor that I replaced before is still running extremely hot. I bought a gigantic resistor to swap in there but it is too big to fit in that spot. I can put it in kind of around things. Is that a good idea? I don't like it running that hot. I have attached a couple of pics so you get the idea.

 

[larryderouin]

I swapped the transistor today but managed to snap the resistor next to it in the process. Orange orange orange gold is 33k, right? I ordered a batch of those and will get that swapped when it comes.

On another note, the large 330k resistor that I replaced before is still running extremely hot. I bought a gigantic resistor to swap in there but it is too big to fit in that spot. I can put it in kind of around things. Is that a good idea? I don't like it running that hot. I have attached a couple of pics so you get the idea.

Yes for the 33K.

Not a good idea for the 330K putting a 5w resistor in there. Better to determine if the wattage on the original is correct 1st, and 2nd determine the actual current flow thru the circuit. If it's within limits leave it alone. I would raise it up away from the board a bit to help with airflow around it.

 

[EastPoint]

I managed to fix this three years later. It's funny how intimidating that receiver was back then and how easy it is to work on now. Thanks again for everyone's help on this one.