QX 949A Quad reciever

juddboz80

Active Member
Hi, I'm a new member and look foward to being on these boards and don't have a lot of knowledge on working on these.....

I recently got a pioneer qx 949a quad reciever, it is in great cosmetic condition. I'm looking into setting up a quad system.... Hooked everything up and it has crackles when adjusting the switch between phono, aux, tape, and radio... Other than cleaning the pots is there anything else I can do to make sure this amp is in great working shape?? I'm an electrician so I do have some knowledge in electronics, any help is appreciated!
Anyone have one of these?? Any tips on this unit??
 
Get the SERVICE MANUAL for it. There are Transistors on it that cause the problems you have and other problems. These are MUST REPLACE before they crap out and take the unit with them. REPLACE the 2sc1451's in the Main Amps (all 4 of them). And any 2sa725's and 2sa726's on any boards that have them. If you come across other pioneer's one of the 1st things to do is look for these and replace them.

2sa725/2sa726 = KSA992
2sc1451 = KSC3503.

NOTE and I cannot stress this enough. The pin layout on the NEW transistors is different than the originals. Download the DATA SHEETS for the new ones, and compare the pinout with the board and the old transistors. Adjust pins to fit in the CORRECT holes without touching.

Read this thread http://www.audiokarma.org/forums/showthread.php?t=43186 pay particular attention to POST 11.

Once you've got the transistors done, rebuild the power supply (caps, transistors,) Test resistors with one side lifted. If out of spec replace.

with it being 40years old, I'd rebuild the amps, protection circuit, tone control board, and equalizer board (phono preamp). Mainly recap, but the troubleprone transistors get priority. No parts lists that I know of. So you'll have to make your own. Stick with a known good distributor like Mouser, Digikey. Use Good quality electrolytics, no need for Muse or Silmic II's. They won't make it a 1250/1280 in SQ. There may be small (<4.7uf/50v) SKY BLUE Sanyo caps in it. these are KLUDGE and have a tendency to short into resistors (capsistors). Get rid of them and install 50V panasonic ECQ-w stacked films. Never need to change again.

Mark the FIXER's "Rule of Thumb" regarding caps in PIONEERS'
Cap rules of thumb (nichicon)

I use upw, uhe for general caps including signal coupling in that order depending upon stock "cea"
I use ues, uep & uvp in that order for bipolar depending on stock
I use ukl for low leakage caps (in sensitive areas they reduce the noise floor)"ceanl", "cssa", "csza"
0.1uf to 2 uf I use stacked film where they fit: DFS and ECQ

solid aluminum and tantalum caps get stacked film when possible, or ukl's otherwise. "cssa" "csza"

c?B means it's an axial cap = one lead on each end
c?a = radial = both leads on one end

Download the PIONEER "TUNING FORK" Service Notice's from this sticky thread Bunch of good stuff that explains the caps designations etc.
Service manual, schematics, and some general technical bulletins here
 
quad

I briefly owned the little qx 747.i did like it a lot.However it developed static hiss in the phono stage first.After a month it spread to all modes.there are a couple transistors that ran hot after a few minutes.i took it in for an estimate.(a well known vintage shop)it was $800!..they stated it was not worth it as it was extremely hard to service.the tape monitor switches needed rebuild,,Dolby, all caps , ect..too bad, as cosmetics go, was mint.I have no knowledge of repairing electronics.I do miss it.You fellows have the edge.Good luck.
 
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juddboz80; Before digging in to the transistors, caps etc., Clean all the front and back panel switches, pots, etc. with Caig DeOxit (D-5), and Faderlube (F-5). READ HIS THREAD 1st! http://www.audiokarma.org/forums/showthread.php?t=207005
CLEAN EVERY POT, SWITCH. If it goes UP/DOWN, IN/OUT, Round and Round, it gets cleaned.

Then test. If the problem clears up , you bought yourself a little time to take and research the job while listening to the 949a. Take it easy on it until you've redone it. Then go crazy if you want.
 
I've got started cleaning pots and switches.....just that alone made a big difference! Still got more to go tho. I bought de oxit red and de oxit gold and seems to help a lot....thank you for the tips....really appreciate it!!!!! I'll update when I get into it farther, I really wanna bring this back to life! So far it has a great sound!
 
Just something you might want to keep in the back of your mind. Lesser used units tend to need more than one DeOxit treatment as they tend to gether more dust and dirt on the contacts than a unit that has been used regularly. Open switches and pots also tend to gather contaminants faster than sealed switches and pots.
 
This place is awesome, why did I not know about ak before?!?!?!?
Thanks Larry for all your help, I've now cleaned everything I can possible clean... I let her sit overnight and woke up today and blast off!!!! I don't have the quad hooked up to 4 ch now but it has a 2ch/4ch switch that can be flipped but with this on 2ch and on phono input this reciever sounds amazing!!!!! Tuner works and sounds great, but I need to check it out in 4 ch....I'm gonna play records on her today to give her a test run and see how she sounds after letting her get hot....should I bring her up slowly ??
 
Not necessary. The 2-4 block on the back just spreads out the B+ to all 4 amps and drops it a little to feed them all. Go ahead and use it sensibly and check the rear channels for problems. If no problems let her rip.
 
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