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pustelniakr
03-04-2008, 02:14 PM
I hate to follow a hack technician. Their results are generally like the proverbial box of chocolates (you never know what you are going to get). I have been sitting on this beautiful Pioneer SX-950 for about 2 years, waiting for the right time to bring it up to full steam. It is cosmetically pristine, but the FM sounds like __________.

It is finally time to open her up and I'm encouraged, the FM front end was pretty much out of alignment, but dialed in nicely. I get up to tweaking the IF transformer, and I find the reason for the season: a messed up IF transformer. The slugs would not move. I was finally able to get the top slug to move (it had been driven tight against the bottom slug). However, the bottom slug just would not move, so I decided to take the transformer out for some intimate moments. Lo and behold, the bottom slug was fractured and driven into the bottom of the tranny. Since the transformer has not been available for over 10 years, that stinking $.50 slug just became worth about $600. I had to finish breaking up the fractured slug to get it to let go of its hiding place.

Here is where over 125 pieces of old broke audio gear, stacked up all over the house, comes in handy. I found that the Pioneer TX-7500 tuna uses the same IF tranny. I remove the top slug from the 7500 tranny, and behold, it is only 2/3 the length of the top slug I took out of the 950. The hack had fractured the top slug too, and replaced it with what he had laying around :sigh:

Once I got a chance to view the underside of the tuner board, I saw further evidence of "hacking". Nothing I can't find or reverse...lets just say he left a bread-crumb trail.

So I took both slugs from the 7500 and in they went, to the 950. The tranny went back in, and the alignment went smooth as silk. Now she sings so pretty, it is simply amazing. The only problem is: now I have a perfectly good TX-7500 that is a paper-weight, since her slugs are now missing :no: Time to peel the eyes...

Enjoy,
Rich P

PS. Pics will be forthcoming, once I get the SX-950 fully restored, recapped, and re-assembled. She really is cosmetically pristine, which is rare for these, in this day and age.
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Mark W.
03-04-2008, 04:02 PM
As time goes on I wonder if the higher end models will actually be in better supply and nick due to sourcing parts from the lesser value Mid level and BOTL units. Not that I wouldn't be the first to do exactly the same thing. The SA-8100 I parted out due to some guys wire cutters and wire nut hack job. Has saved a half dozen SA-8100's and SA-9100's including a couple RIch has made sing again.

Just an observation.

markthefixer
03-04-2008, 06:03 PM
I<snip> The only problem is: now I have a perfectly good TX-7500 that is a paper-weight, since her slugs are now missing :no: Time to peel the eyes...

Enjoy,
Rich P


Rich, the 950 uses the HA1137 fm detector I.C. and just about all the Pioneers that use that chip as a detector (and a LOT do) have the same FM IF (discriminator) transformer T73-035.

I started by verifying that both the sx-535 AND sx-550 use that exact transformer... and you just gotta believe that if it is used in that lowly of a unit, that it is replicated UP the line... through at least the 950.

Now I had HOPED that the parts I had saved from the sx-550 I stripped would include that transformer, but my hopes were dashed as it seems that those were probably the ONLY parts not included in that parts collection.... I can't understand why I don't have it, because I even salvaged the main tuning capacitor !!

The upshot is that there should be a LOT of them around....

The units that use it (verified by SM) are:
sx-424, sx-626
sx-535, sx-636, sx-737, sx-838, sx-939, sx-1010
sx-550, sx-650, sx-850, sx-950

The units that do NOT use it (verified by SM) are:
sx-525, sx-727, sx-828
sx-750, sx-1050, sx-1250
sx-680, sx-780
sx-3700, sx-3800

pustelniakr
03-05-2008, 04:36 PM
Thanks Mark. That is good info to know. I only have the manuals for the gear I have, and that is mostly upper end stuff, which I would not want to turn into parts units :no:

I do have an SX-838, but that one is in super nice condition too, and is next in the queue for sweetening.

Enjoy,
Rich P

markthefixer
03-05-2008, 07:22 PM
Thanks Mark. That is good info to know. I only have the manuals for the gear I have, and that is mostly upper end stuff, which I would not want to turn into parts units :no:

I do have an SX-838, but that one is in super nice condition too, and is next in the queue for sweetening.

Enjoy,
Rich P

Here's hoping that one that has already been started down the parts path will yield a donation.....

pustelniakr
05-27-2008, 02:54 AM
Well folks, the SX-950 in question has just been buttoned up from its complete restoration. She turned out super sweet. I thought I would fill you in on what was required before she was finished:


You already know about the MPX transformer slugs which the hack tech had totally botched and mis-replaced
Next was to reverse the jumpers and various components put in to make the unit sort of produce FM with the MPX tranny so hosed up
I then noticed that Q8, the HA1196 (PLL FM Stereo Demodulator) had been swapped out for an ECG (Yuck!) sub: ECG1484. That was re-replaced by a true Pioneer HA1196.
Next, I find that the FM sounded real nice, once the FM alignment was re-performed correctly. However, after an hour or so of warming up, FM started getting extremely fuzzy, like when a single-ended amp is losing its supply rail. I found that Q6, an HA1137 (FM IF system in a chip) was having thermal issues. I replaced it with an original Pioneer IC as well and that solved the thermal problem
I then replaced a fried resitor, R6 (150 ohm, 1/2 W) on the power supply board. Since this part was probably the source of the problem the previous hack was trying to solve in the 1st place (a bit under-rated), I replaced it with a 1W flameproof metal oxide (fits in the same space).
I upgraded the 2SC1318 supply transistors (Q3 & Q5) with 2SC1384 transistors, for higher voltage and current handling (Q5 is known to have problems due to inadequate derating)
All heatsunk transistors in the unit got their heatsink compound refreshed
All circuit board solder joints got refreshed
All electrolytic capacitors were replaced
Any tantalum caps in the signal path were replaced with low leakage 'lytics
All incandescent lamps got replaced ( I went just a bit brighter on the source, speaker and stereo indicators, since they were a bit dim for my tastes)
I then took the time to dial in the tuner to a nat's behind, and set the amp's bias and balance
A bit of finshing work: cosmetic detailing, and now she is good as new (if not just a bit better)

Folks, this receiver is definitely one sweet music machine. The tuner is now super sensitive, and so clean, I could almost mistake it for a CD. She has some serious thumping power too. She will be going with me to my lab, at my day job, for some serious enjoyment, until further notice :guitar:

Enjoy,
Rich P

pustelniakr
05-27-2008, 03:13 AM
Here she is, in all her glory:

http://www.audiokarma.org/forums/attachment.php?attachmentid=92684&d=1211879571

My thanks go to the following, for their help in this project:


MarkTheFixer, for letting me know that the MPX transformer was available on a variety of lower end receivers
Grateful, for selling me the SX-650 tuner board, from which I got the necessary 2 ICs and MPX transformer slugs

Enjoy,
Rich P

pioneervato
05-27-2008, 06:38 AM
That is a great looking 950. Very nice work indeed!