QX949 Restore

calman46

calman46

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The 949 was made 1974-1976. The 949A was 1977-1979. It would appear by the manufacture dates that the 949 may had issues. I have the 949 and both service manuals and Pioneer beefed up power supply A board on the 949A. C1 was changed from 1000uf to 2000uf, Q1 was changed and so were D2, D3 and the stand-alone fuse board was deleted, and the fuses moved to the power supply A board. The mA's was reduced to 100mA from 150mA on +B4. Both power supplies have the same voltages, but the layout is a little different. I'm still studying the schematics as I'm not a tech. I'm thinking I will change my 949-power supply to a 949A. The top mounted decoder board was changed from two boards to one board on the 949A, so that stays the same. My QX949 works (after working the micro switch) and had the scratchiest volume control I have ever heard. So, I am going to recap and replace transistors on this 50lb QX949. There is a heat stressed cap on the power supply board A. This kind of confusing without looking at both schematics. I'll post the 949A later upload_2022-1-26_8-12-33.png
 
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After looking over the schematics of both QX949 and QX949A it now seems that Pioneer redesigned the "quadraphonics" boards/circuity and the power supply to match them. So, I'm staying with the original QX949 layout. I'll be back
 
They improved the SQ decoder in the 949A by adding full-logic circuitry. That provided much improved front to back separation in the SQ mode.
 
I'm working on the sub-channel board now and found all the 2SC1312 transistors lettering is just about worn off. Could this be from heat? The other transistor's lettering is good.
upload_2022-2-5_8-59-28.jpeg
UPdate it's like the 2SC1312 were sprayed with something, maybe freeze spray? The lettering on some is totally gone.
 
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I'm doing some homework getting ready for the power amp boards. I noticed that Pioneer used lower voltage components (drivers, outputs etc..) on the rear speaker's amps then they did on the front speaker's amps. I'm thinking they did this because the front amps need to handle the power increase of the 2CH power boost option. I'll just use the higher voltage ratings for all. I haven't decided to do the output transistors yet. $65, you know. This what I have so far for replacement transistors. I haven't pulled the boards yet, so I don't know what is actually on them. What do you think?
Original Replacement
2SC1451 = KSC3503
2SD358 = KSC2073
2SB528 = KSA940
2SA726 = KSA992 matched hfe
2SA869 = KSC1845


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So far so good. The tuner board was tricky, but I was able to recap it without disconnecting the dial string. On to the power amps
 

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Filter caps, back in. Bias and DC offset, set. All is good, unit still working.
Need to do some cleaning, I/O jacks have nicotine on them but there was none inside unit? Could this mean no air flow inside. I have 4 recapped Pioneer CS-88A for this QX 949. Unit sounds good with headphones (either jack) on FM.
 
Doing the foam surrounds on the 3" tweeters 8 of them. These surrounds were not available when I "dragged " these home from the Fleamarket. These little surrounds are a tricky to do. The CS-88a have those nice FB cones on all . There is 5uf cap in the x-over. I have 4.7uf and 5.6uf ,which would be a better choice? thanks
IMG_20220321_084323.jpg IMG_20220321_084618.jpg
 
I hooked up the QX 949 to 4 CS-88a's and a CT F9191 (top rack out of picture). Played FM local station on CD-4 mode , nice defined bass first thing I noticed . FM plays surprisingly loud. I tried all modes , 2-ch. CD-4, RM, SQ. I like CD-4 has an open sound to it with good imaging . The CT-F9191 sounded very good also but needed a little more volume again the CD-4 mode is my pick . I'm going to split the tape deck's output and try the 4-CH tape option. I'm going to test all the QX 949 modes and options with different media and music .I'm thinking classical music will come alive . I have the rear speakers on the outside in the picture so my test setup is not correct. Dial pointer light is out but everything else seems to be working . I will test the 2-channel power option at some point but I can't imagine it would be an improvement. IMG_20220327_124942.jpg .
 
So, lining up all 4 speakers is an optional setup, per owner's manual. The more time I spend with this QX 949 more I realize I knew next to nothing about Quad.
 
The front amps play louder than the rear amps. I can adjust them some with the meter display but there is diffently a difference. According to the specs all four should be equal. I am using FM. I need to check voltages. I didn't replace the relay.
 
Keep us posted.
Love the 4 CS 88's

My quad collection contains a QL 600a, and a 240 standalone CD4 decoder.

I currently switch between a QRX 7001 and HK 800+. I use the receivers 4 channel inputs, and have evolved to the rather amazing Involve Audio Surround Master decoder ( with the Quadraphonic Quad SQ LP version )

My QL 600a should have the more/most advanced Pioneer SQ decoder.

It's good, not as good as the Sony SQD, and certainly not as good as the DSP decoder in the Involve..

But, I would LOVE to have your reviever in my collection

:)
 
So this is where I'm at . The front amps play louder than the rear amps . The front level controls effect each other . The rear amps (R&L) output is not the same but the level controls work independently .
 
i owned one of those new way back when. and i do now but only use it in 2ch,mode. those level controls are set up using a cd-4 test record that came with the receiver as new. you are supposed to also use a shibata stylus. my shure v15-III at the time worked just fine. conventional wisdom of the era and my FOGGY memory tells me that depending on what mode you are cd-4,sq or rm or 2 ch (and dont recall which or if it was all of them) there is INDEED a difference in power to the rear speakers, in fact the salesman in '74 recommended i could save some bucks when i at the same go was buying speakers and i opted for cs99a's and cs88a's for the rear channels. unless i missed something that you were trying to say or i dont understand i'd say that you dont have a problem. you might get on hifi engine and have a read of the qx-949 owners manual as it might clarify what i am trying to recall. i rebuilt the one i have now and have a test record i got on ebay and after the rebuild it all worked just fine. whatever you do DONT monkey around with any adjustments on the sub channel board. there is NO data in the service manual nor could i get the information here on ak or even doing a google search on how to align it i was told that that info was proprietary, top secret, for airforce generals only. enjoy the set they do sound nice dont they?
 
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I thought the lower power to the rears was correct also but with the front level pots effecting each other can't be correct .The rear amps also sounded dull and no bass. I have 2mV DC offset on all 4 amps but the protection will relay trip for a second or two . Its acting strange now . One rear and one front channel is showing a low level light on the meter , this is with no input signal. It seems like something is shorting . I've been looking at the wiring . The owners manual states 44watts with 4 channels driven into 8 ohm.. The preamp and amps appear to be working correctly they're just not getting the correct signal I think. .Looking at the schematic I think the sub-channel board is for phono only . So with out a quad cartridge and the disk. I'm not adjusting anything there, but thanks for the tip . I noticed there is CD-4 decoder alignment in the SM.
 
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