Restoring Pioneer sx-1250

Just following along trying to learn... The service manual shows Q8-Q11 all using 2SC945A-Q and Q7 using 2SC1312-G. I realize the numbers Mark gave are modern equivalent numbers, but shouldn't Q8-Q11 be the same number and Q7 be a different number? Maybe their is a mistake in the service manual?

craxx6969,
transistors on that board were physically damaged; (see post #1)

Mark,
thanks for your help. I do have plenty of those. It's always good to have extra.
Thanks

buildingnut,
I'm sure you'll get an explanation from Mark!!!!

karel.b said:

craxx6969,
transistors on that board were physically damaged; (see post #1)

Mark,
thanks for your help. I do have plenty of those. It's always good to have extra.
Thanks

buildingnut,
I'm sure you'll get an explanation from Mark!!!!

Click to expand...

Whoops, should have read the entire thread.. You're in good hands with Mark..:thmbsp:

buildingnut said:

Just following along trying to learn... The service manual shows Q8-Q11 all using 2SC945A-Q and Q7 using 2SC1312-G. I realize the numbers Mark gave are modern equivalent numbers, but shouldn't Q8-Q11 be the same number and Q7 be a different number? Maybe their is a mistake in the service manual?

Click to expand...

Replacements consider many things; the original (bean counter driven) transistor choices AS WELL AS the function of the transistor in that location and also includes experience with failures found over the years in that location. Like - was the choice ill considered (or too expensive) for extreme (30 years to them IS extreme) longevity.


Q7 carries the FM audio and subcarrier, and is lower noise

Q8 and q9 are part of a muting "logic" circuit and can be noisy without consequence

q10 drives the muting relay coil (and really should have a flyback or snubber diode now that I think of it) thus has a higher current rating and power dissipation.

q11 is another "logic" which kills the FM's stereo decoder PLL oscillator (vco) when FM is off.

Thanks for the explanation Mark, I was sure I was missing something. A lot to learn and we are all very lucky to have you as our mentor!

Installed new transistors as per MTF, put 1-5mm core in T1 and 2-5mm cores in T2 and using my DMM, signal and tuning meters on the receiver (plus my ears) and FM tuner adjustments directions (page 36), I aligned all available FM stations as best as I could. There is a 0.05MHz (or less) discrepancy on the FM scale from 88MHz to 108MHz on very few FM stations; 108MHz = right on, 88MHz = -0.05MHz, but that is as best I can do without any other instruments; (signal generator, distortion meter, MPX signal generator and oscilloscope).
I'll be doing more tests (phono1+2, auxiliary, tape1+2 rec. and play) in the near future, I hope and I'll keep you posted.
Thanks

Well done Karel!!

Yea, That goes for me too!

Thanks guys and special thank to Mark and Rick. Also mattsd's parts list was very helpful, thank you.
Basically, I replaced ALL transistors, electrolytic caps (incl. the 4 - 22000mF/100V cans) and most diodes using mattsd's and Mark's parts lists. Working on the 1250 is lot easier (plug in boards), then on the 1280.
I hope I'll have more time to write about the tests tomorrow. Now I have to tend to my better half.
Thanks

Good man! Making the other half happy, makes for longer hours to spend on the hobbies.
The 1250 is a great set in every which way! :yes:

OK, here I'm again.
The caps I used were: Elna RFS Silmic II, Nichicon KZ and UKL, Jensen axial (470mF/150V in PS) and the big 4 : Nippon Chemi-Con. All caps were upgraded to min. 35V, except where they would not fit due to a size. Some caps in stabilizer ass'y (C7, C8) were upgraded to 100V from 50V.
Resistors that normally run hot (but not specifically) were replaced with higher wattage (1/2W to 1W, 1W to 2W, 2W to 3 or 5W) metal film, metal oxide, flameproof, also some wire wound. Replaced old semi-fixed with new Bourns trimmers.
Used mostly Fairchild semiconductors and some ON Semi (in stabilizer ass'y).
Cleaned ASR-015 relay and replaced ASR-010 with new Omron.
Replaced all mica insulators and applied new silicone heat sink compound.
Cleaned all switches and pots with Deoxit D5, G5-gold and F5 Fader.
Result? Absolutely terrific.
Tight base, clear mids and treble, presence. Everything works perfect (with couple of exceptions), which I'll describe tomorrow.
In my opinion, the 1250 is little better sound-wise then the 1280, but again, it is only MY opinion!!!!!
One thing I wanted to mention. If you ever want to replace PL1-PL4 lamps (AEL-056) on the 1250 or 1280 with LED's from ebay, they do'nt fit unless modified!!!! For the 1280, all 4 are too long. The 1250 the two outside ones are also too long. Just be aware of it. There is a way to modify them, if you handy. You can also buy them from your local electronic store. I've got them for $4.00 can. a pc.. They come in yellow, white, blue, red, (green?).
Thanks for now

As I wrote in previous post, there are two glitches and both involve the phono 1 and phono 2 push switches and "possibly" the equalizer amp. Although I cleaned all switches and pots very thorougly, I'm getting a pop in both channels turning the P1 or P2 to ON pos., and ON only. Higher the volume, louder the pop. Once ON, there is no problem, my turntable works perfectly, sound is excellent.
The other glitch: When I play my CD's (CD player is hooked to auxilliary), then switch to phono1 or phono2, I get the pop and then I can hear a residual music from the CD player, more from the right channel, but not much more. Again, CD player works perfectly, sound is exellent.
I,ll clean the two switches again, see what happen.
Any ideas? If you do, please let me know, I would much appreciate it.
Thanks in advance

Could it be as simple as the AUX input wiring being too close/running parallel to the PHONO inputs? The CD likely outputs could be nearly 2.0V P-P and the phono amp section is a LOT more sensitive, with a much lower signal threshold at 2.5 mV. The FSM shows the phono stage gain at about 52dB overall, and 35+dB of that is just to get it up to the level of the AUX inputs.

I only mention this because I had a similar occurrence in a SX-950. Grounding of the input coax was good and just re-routing the input cables helped reduce the problem to a point where the "extracurricular" noise was not apparent until almost full volume was achieved.

That's what I was thinking!!
I'll check the grounds on both phono inputs, also how close they are (wires) to the auxilliary.
Thanks Watthour

Some clicking when you switch the phono circuits on is normal, mine does it too. Normally you don't have the volume way up when you change inputs. As far as sound "leaking" between inputs, that happens too but should not be noticeable under normal operation.

You don't normally put on the tape or phono inputs and also run something in the Aux input. Normally you would turn off the CD player feeding the Aux input when using phone or other sources, right?

jeffpaletz,
You're right!! All that was done just for testing the unit for any problems.
Thanks

I cleaned the phono1 and phono2 switches again (the full treatment). Checked the signal wires, both, phono1 and aux. from the RCA connectors to the function ass'y board (AWS-094), then phono1 to the phono amp (AWF-021), then to the flat amp (AWG-042); checked the phono2 from the RCA conn. to the mic. jack ass'y (AWX-097), then to the phono amp. Checked all the grounds related to these connections and I could not find anything that would indicate a problem(s).
I came across a thread posted by PREMIUM PLUS in 2013, where he asked for a help with the same problem. It seems to me, the problem was never solved?????, but I may be wrong. All I know, this guy was a technician/repairman with a lot of equipment.
Question.
I use deoxit gold G5 for switches and fader lube F5 for pots. Is it better to use fader lube on switches as well?
Thanks for any help, direction, etc.

Karel,

I think that you will never solve the source cross-talk issue. Why? it is the design of the switch, proximity of the contacts to each other, stray capacitance. If I refer to my "Self on Adudio" book he claims around 71-74dB isolation. I have never measured switch isolation, for these Pioneers, but if you try compare your 950 to the 1250, i think that you will find that they are about the same. They use the same switch assembly IIRC.
You could bring down the CD level as a quick fix.
Are you sure all that junk, that you are spraying is not creating more cross-talk?

The cross-talk remains only on phono2 and only on right channel, but it's minimal, with high volume only. Phono1 is clear. I separated the signal carrying wires as much as I could and it's OK now.
The problem is the popping sound in phono1, phono2 switches and to a lesser degree in aux. switch.
As far as the cleaning the switches, I thought Deoxit was the only cleaner specifically made for it and that's what I used.
Thanks Rick
PS
Read the thread from PREMIUMPLUS in 09/20/2013, Pioneer sx-1250 function switches pop.