Pioneer TX-900 Restoration

Below is a nice little Tuner I picked up off of Ebay over the summer.  I’ve been wanting to collect an early example of top of the line Pioneer pieces from their early days.  This particular series matches my SX-1500TD nicely and I always had a liking toward the styling of these units.  The matching SA-900 amplifier is a perfect match to this.  Now if I could just find a matching turntable.  Anyone know what model?

Pioneer TX-900 Tuner

Above photo is after the restoration, but before I repainted the cover.

When I received this tuner I was hoping like anyone that it would just work out of the box, but as expected it couldn’t pick up anything.  Upon closer inspection I noticed that it looked like it had a ton of hours on it.  The signal strength meters had heat stress to the white plastic causing the meter cases to turn a brownish color from the heat generating off the lamps.  Someone made a horrible attempt at replacing the indicator light on the dial pointer, and it was filthy on the inside.

The first thing I did was clean the thing up.  The results below looked cosmetically better, but still the performance sucked.

TX-900 Internal view

 

  • With the assistance of a good service manual I started to get a parts list of capacitors to replace.  I figured If I’m going to do this, I’m going to recap the whole thing before I waste my time trying to align it.  The picture above actually is after I had recapped it.  The replacement electrolytic caps are about half the size of the originals.
  • After replacing the caps, I noticed that the tuners alignment didn’t seem to be off as much.  In fact the biggest improvement came after working on the power supply section.  It still wasn’t exact, but improving none the less.
  • Moving on I finished up with the caps and proceeded to do some alignments on the FM section.  This was one of the first tuners I ever attempted to do an alignment on so I followed the service manual and did lots of reading to understand what I was adjusting and how it affected the circuit.  Using my scope I looked at the 10.7 Mhz IF freq coming from the Front end tuner into the IF amp.  Not wanting to mess with the front end, I left that alone and confirmed I had a signal.  I followed it through the various IF stages making sure the it was being amplified properly.  There were only 2 adjustable transformer coils so following the manual I adjusted those for maximum signal.
  • With a strong signal on a known station, I noticed that the center tuning meter was off and the dial was just a hair off too.  I then made a slight adjustment on the front end tuning capacitor to move the station to the right spot on the dial.  Confirmed maximum signal through the IF stage and then figured out which one of the adjustment iron cores to the larger transformer affected the center tuning meter.  The last transformer has two iron cores.  One will adjust the center tuning meter, and the other affected the signal strength meter.
  • Then I replaced the indicator pointer lamp with the correct lamp, and installed a yellow LED and resistor for the stereo indicator lamp.  I had a hard time finding the right low voltage, low current, incandescent lamp that was bright enough to be seen.  I found that a yellow LED worked better.  As for the dial pointer, I stayed with a standard lamp because the tuner was designed to brighten and dim the pointer as you changed channels.  An LED really won’t dim properly with the way this circuit worked so leaving it alone worked the best.
  • Replaced the fuse type lamps on the ends of the faceplate dial, and finally repainted the cover.
  • OH the AM section!! I didn’t spend much time on this,  It pulled in stations really good, and the dial was accurate so I left this one alone, just recapped the components in the AM tuner section and called it a day.

In the end, I know that the professional tuner guys would and could elaborate on the proper methods and tools needed to do a tuner alignment.  But with the tools that I had available, the fact that I limited my adjustments to minor +/- 10~20 degree turns and the fact that the results were favorable I think I did a reasonable job in restoring some life into this piece.  One night I was easily able to pull in a station from across Lake Michigan with an outdoor antenna.  That same night I compared it to my Pioneer F-91 tuner with this same station.  The results were good, both tuners picked it up with similar interference and sound quality.  Even the signal strength was similar assuming you interpolate between and analog meter and the digital meter.  Bottom line, this tuner sounds better then the stock, untouched 30+ year old tuner in my SX-1500TD.  In fact both tuner sections are similar in design so they should theoretically sound almost the same.  As for the F-91, the F-91 is more detailed in the high end.  The TX-900 is just a hair bit softer in the high end frequency response.  Also its a bit more mellow sounding in the midrange, but very enjoyable to listen too.

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