Pioneer QX-949A 'Scope" lamp replacement

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BobC63

New member
Joined
Oct 21, 2019
Messages
6
Location
Lehi, UT
Hello all -

I recently procured a Pioneer QX-949A that is in overall very good shape other than needing the usual cleaning and Deoxit treatment.

One issue I have noticed is that only 1 of the 4 "scope" lamps lights up / seems to be operational. For the record, I do get sound to all 4 channels, it seems to just be blown bulbs in the "scope".

Does anyone have any information / guidance on how best to remove the 'scope' mechanism from the chassis? It seems that in order to even replace the 4 light bulbs in the "scope" it must be removed and the bulbs themselves are actually hard wired in place...? YouTube has not been very helpful; a fair number of videos about this receiver but nothing related to scope repair, etc.

My first post here on QQ, and my first piece of quad equipment - been a vintage (stereo) audio hobbyist for a few years now. Hopefully I can get this big beauty back to fully functional, and start enjoying some sweet quadraphonic sounds!
 
Yes, thanks, I actually have already downloaded and printed the service manual out (Was fortunate that the original User Manual came with the receiver). Schematics on it are rather complex, not much guidance on the actual "how to" remove the scope apparatus and access the bulbs. I'm hoping someone here may have actually done this repair themselves and might have some tips..?
 
Looking at page 43 of the service manual seems to indicate that two screws on the left side of scope and one on the top will remove the scope after you disassemble the top wood case, bottom metal plate and removing the face by removing screws and knobs. Then according to page 44, you remove two screws from the front of the scope to remove it from the bezel plate. Page 102 seems to show part number AAw-021, the "4-CH Level Indicator" is a whole unit. the lights appear to be running on 7.5 volts AC. Doing a search on ePay I see sellers using 3mm LEDs in the receiver. I suspect you will just have to disassemble it and see if you can retrofit new grain of wheat 8 volt incandescent bulbs or LEDs. There are a lot of internal parts on the auction site but no 4CH level indicators which leads me to think they go first or at least very commonly.
 
Thanks, that actually helps quite a bit! First time I have been able to see what the 4 Channel Level Indicator looks like disassembled... Right now I am assuming that the level indicator mechanisms all still work, and it's just 3 dead bulbs. Either way, now I can study the indicator unit ahead of time and figure out where to clean it up, how to access the sub-assemblies, etc. before I actually tear into the receiver. Sweet!
 
OK, so I finally had the opportunity to tear into my QX-949A. Disassembly was fairly easy (thanks for the help, QQ!) and I was able to replace all 4 of the 4- Channel Level Indicator bulbs (even though 1 bulb still worked I figured why chance it, change them all). Those little aperature covers, though - Wow, what a real PITA they were. In hindsight, I should have never taken the "scope" apart, and simply unscrewed the lamp board from the back of the scope. Those aperature covers are not much more than paper-thin aluminum, and they literally fall out if you just brush up against them. And a huge pain to put back in properly; each side has a tiny 'flap' that has to be tucked into the aperature motor itself -which is not fixed and constantly moves back and forth with every touch of your finger, LOL.
Anyway, got the new lamps installed, put everything back together... and not quite as good an outcome as I hoped. All 4 lamps are lit in the display - and CHannel 1 and 2 work beautifully now.... but the Channel 3 and 4 aperture motors are not functioning properly. Channel 3 appears to stuck fully "open" (fully lit end to end) and Channel 4 is stuck fully "closed" (center point dot lit but length does not change with VU input). Not sure if stupid aperture covers are perhaps not moving freely (#4), or perhaps came loose and fell off (#3)...or if the little motors themselves are not responding correctly, Has anyone ever actually done any work on those little motors? They look rather complex and, unless someone here tells me they have successfully repaired one... I will probably just leave things alone for awhile.
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Do NOT Touch these little sh*ts!!!
 
OK, it's been several weeks since my last update... thought I might share the completion of this project (y)

After months of searching, I was FINALLY able to find someone who had not 1, but 2 spare 4-channel indicator 'scope' assemblies that he was willing to part with! (and at a quite reasonable price, too)... so, I purchased and received the 2 donor scopes. Unfortunately (or maybe not, since I ended up learning some stuff) neither one was 100% operational. Both had 3 good operational channels; and 1 channel with a failed aperture motor. SO... guess what I got to try?

I removed 1 bad motor from one of the donor pieces and replaced it with one good motor from the other donor part. Honestly, that wasn't as bad as I thought it might be. The motors are held in place by 1 tiny screw; and yes, that was a real PITA to remove. Otherwise, it was a simple matter of heating / removing the old solder from the motor terminals, removing the old wires and sliding the motor out of the plastic housing. New motor went in as easy as the old one came out. Then after the screw had been reinstalled, it was time to 'transplant' the repaired donor scope into the receiver.

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Here's where it got a little more interesting. The 'scope' has a total of (14) wires connected to it: (4) leads for the 4 - channel indicator motors; (1) lead for the indicator lamps; (4) grounds for each of the 4 - channel indicator motors; (1) ground for the indicator lamps; and then inexplicably (2) additional leads for the receiver front panel lamp circuits and (2) grounds for those same lamp circuits (!)... basically, the receiver lighting circuitry wiring passes through the scope assembly - instead of simply having a single lead and ground come off the circuit harness to the indicator bulb board. Way more complexity than it needed to have.

Anyway, I had some luck in that (3) of the (4) indicator motor ground wires were still attached to the original 3 'good' motor terminals; so I only had (11) wires to connect, LOL. The main difficulty was that the wires inside the receiver are very short, and the space behind the installed scope assembly is very small - so there was no way my man-sized hands were going to be able to reconnect / resolder all those wires inside the receiver cavity. My solution was to cut some 3-ish inch long wires to use as 'extensions' between the receiver wiring and the scope assembly. This way I could do all the connecting / soldering outside of the receiver, and then carefully push everything back inside the scope assembly opening and (hopefully) it will all fit without breaking any connections or shorting anything out. I also used heat shrink tubing over every solder joint to help prevent accidental shorting of any connections, should those extension wires contact each other inside the receiver cavity...

Here I am using jumpers to test everything out before final installation - it works!!!
(Also note that the "FM" light is out, and the tuner dial pointer doesn't light up... more about those later)
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Several of the 11 jumpers I had to install to make sure everything was 100% operational.
You can see how little space there is behind the opening for the scope assembly
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Once I had all the extension wires soldered in place, I was able to put the scope assembly back into the receiver cavity. It was a good thing that I used the shrink tubing, as all that extra wiring ended up being butted up against each other in the little bit of space behind the scope assembly.

While I was inside the receiver, I took care of the only other issues I had with the unit. I replaced the "FM" indicator lamp as it was blown; and I replaced the tuning dial pointer since the original apparently had broken off years ago, and the previous owner seems to have replaced the lighted OEM part with a non - lighted pointer from some other model. Luckily he had not removed the tuner lamp wiring (he just taped it off...) I was able to find a lighted pointer off eBay that looked like it would fit the QX-949A, and it did.

About 2 hours later, she was all bolted back together and ready to rock! I took the opportunity to clean and oil the cabinet since it was off the unit anyway.

Here is the finished project. Everything works 100% - and I would give the cosmetics overall about an 8.5 out of 10.
The sound is rich, full, and everything I expected from a quality vintage Pioneer unit. Looking forward to years of excellent listening!

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