Pioneer sx-434 would like to recap

[bktheking]

I wouldn't do that, you took pics of the orientation of the wiring and the filter cap leads- believe me, if you had them backward you'd know it.

 

[varox84]

True, but as I said, how I installed the new filter caps is far from tidy cause the replacement caps where small and had really short poles... The wires which were properly wrapped to the original caps I had to solder on top of each other on the replacements. Could this be a problem?

If I dont find any cap polarity issue, where would you look next? Maybe the traces of the PCC where i soldered? to check whether solder went where it shouldnt?

 

[Bill S]

Solder bridge? Check back of PCBs for any solder bridges. Sounds like you have snap caps for replacements. Condiser soldering a lug onto each snap terminal before you mount the wires. Otherwise, that 's a lot of wire on a small terminal.

 

[varox84]

Not really snap ins but just regular capacitors with really short legs... I used these ones: http://www.conrad.nl/ce/nl/product/445898/Radiale-serie-048-elco-25V-3300F

You can see it clearly on the photo how short the pins are..

 

[varox84]

So,

1) I checked for solder bridges and could not find anything..

2) Cap polarity is ok, I was also careful during the process so I am comfortable regarding this.

3) Tried the old filter caps, no improvement.

I read somewhere that whenever recapping the amp board I should be careful with 2 particular diodes (Varistors D1 and D2) . Well I wasnt. I did not know, I read that advise too late. How do I check with the multimeter whether I blew these up?

If these are ok then I will throw the old transistors back in and go on from there...

Thanks again!

 

[bktheking]

Use the diode function on the meter, you will get a reading in only one direction while measuring, the other should read infinity.

 

[varox84]

The two sissy diodes tested ok, both exactly the same... So i'm kinda lost... I will throw the old transistors in to try, otherwise Im out of ideas...

 

[bktheking]

You could try that, maybe the ones you got are fakes- i'm out of ideas.

 

[varox84]

voila! I decided to try each time I took one (new) transistor out and soldered the old one back in... after the second one: MAGIC, my amp works again!

Thanks for all your help, brainstorming was the key here.

 

[varox84]

it was probably just a faulty new transistor as i did not remove all of them... and the amp works already.

 

[bktheking]

Good news, congrats!

 

[varox84]

oh, im not done... i was testing with only one speaker plugged in... I get music from one speaker and the same hum as before from the other speaker.... I will remove all the new transistors and let you know whether I can finally bother you with questions about light bulbs and such..

 

[markthefixer]

This is significant:

AWK-034: Q10: 2SA725: KSA992FBU
AWK-034: Q11: 2SA725: KSA992FBU
AWK-034: Q12: 2SA725: KSA992FBU
AWK-034: Q13: 2SA725: KSA992FBU

The 2sa725 is a BCE lead arrangement, the ksa992 is an ECB arrangement - THEY ARE OPPOSITES!!!!!!!!!! PIONEER'S MANUALS STATING ecb FOR THE 2SA725 are wrong!!!

This is a very big, OLD gotcha...

edit- AND when swapping in and out transistors in the power amp is PRECISELY when the "light bulbs and such..." is NEEDED. The low power of the 434 is the only reason bigger problems have not occurred.

The stuff below is just so that we are completely on the same page. Copy and paste, so some may not be exactly appropriate to this situation.

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

 

[varox84]

HA! the legend comes by pops a few words and voila... mystery solved. Thank you your greatness!

 

[bktheking]

What datasheets was I looking at I wonder, could have been the the manual as mark pointed out? Could have sworn the were ecb, usually I catch that, my sincerest apologies . So swap it the leads around on the new ones, insulate a lead to be prevent shorting.

 

[varox84]

I did not understand the following two comments:

1)

AND when swapping in and out transistors in the power amp is PRECISELY when the "light bulbs and such..." is NEEDED. The low power of the 434 is the only reason bigger problems have not occurred.

What do u mean?

2)

So swap it the leads around on the new ones, insulate a lead to be prevent shorting.

What do you mean by insulating a lead to prevent shorting?

Thanks!

 

[bktheking]

In order to use your new transistors, as mark pointed out, the lead arrangement on the new ones are different. You will need to make sure the leads are in the correct holes, E AND B are swapped.

This statement- The 2sa725 is a BCE lead arrangement, the ksa992 is an ECB arrangement

Looking at the front of the transistor- the flat side, left to right is ECB. The old ones were BCE left to right. So you need to make sure E and B are in the right place when you install them on the board. If your markings are the same on the board as Mark posted you may not need to insulate a lead- The leads must not touch each other.

 

[Loalaweiter]

Tuner: If the tuner is working leave alone, other than the few caps that Mark the Fixer will allude to.

There is some excellent advice. I currently am refreshing capacitors to keep alive the SX-434 of my childhood and just held my soldering hand in time.

Which capacitors could be changed on the tuner board without voiding tuner calibration?