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CT-F1250 Fast Forward Repair

Cody Shive

Cody Shive

New Member
This is a short thread detailing an issue I found with my CT-F1250 where Fast Forward mysteriously stopped working. I detail the troubleshooting and the fix. This might help folks whose Rewind or Fast Forward mysteriously stop working.
 
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I restore a lot of these decks, but I focus on the CT-F9xx series mostly. However, I do work on the CT-F1250 from time to time, and I've retained one of them for my audio stack. Normally, for any restoration on these decks, I start with the mechanism whose belts, tires, some springs, pinch rollers, and switches are tired and need attention. Once I've tuned-up the mechanism, I hit the electronics occasionally recapping entire boards or only certain areas giving trouble. It's important to note that I have pulled electrolytic capacitors, during a recapping exercise, only to find many are in better spec than the "audio quality" caps I buy from Mouser. Pioneer built these decks for the long haul; and after 40 years for many of the electrolytic caps to measure dead-on is a testament to their quality.

So, I use my CT-F1250 almost every day. And yesterday, it mysteriously stopped fast-forwarding the tape. Rewind worked fine. Take-up worked fine in play mode, which told me the mechanism wasn't having trouble. Putting it on my bench, I found the rewind/take-up motor was working (which runs at two speeds, depending on input voltage, and when voltage polarization is reversed it rewinds). In rewind, the motor was supplied with ~14.4 VDC; however, nothing for fast forward.

Clearly, this was an issue with the control board.

The take-up motor has two wires: blue and red. When in rewind mode, blue to ground measures ~14VDC. When in fast forward mode, red to ground should measure ~14VDC.

Reviewing the schematic, there are two companion transistors, Q531 and Q530 for rewind and fast forward respectively. The collector on Q530 should measure ~14.4VDC. It didn't, so that was the problem (so I thought). It's a 2SA934. I have some stock on those, but the pulled 2SA934 tested fine on my M-Tester. But the replacement didn't fix the problem.

So, I traced further up the board to find another two companion transistors, Q529 and Q526. Both are 2SC2060. Uncertain I had found the issue, I simply swapped them. Now, rewind didn't work, but fast forward did. There's the problem.

Now, while I have a lot of NOS transistors, I don't have everything. I cross-referenced the 2SC2060 and found I had a dirt-cheap S8050. Pinouts were different for base and collector (so I had to carefully cross them over w/o touching).

I'll include some pictures of the work and transistors.

I hope this helps folks keeping these beautiful creatures alive, kicking, and playing (and recording) our favorite mix tapes!
 
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I have not done a lot of recaps but I have noticed the caps that go bad are low voltage, small ones.
 
For electrolytics, they've been all over the board. I have found nearly all the 1mfd and 10mfd to be off around 30%. There are a handful of NP electrolytics, and they are typically bad as well.

I'm not ruling out weak or failing transistors. Yes, transistors are hearty; but they do fail. Sometimes the culprit is a bad diode (found that on the power board in one of the 950s I resurrected), and if you find a shorted cap in its path, that will clobber a perfectly good transistor. So, it pays to survey the components surrounding the failed transistor.

In this case, the S8050 is about double the hFE as the weaker C2060. Caps surrounding it measured fine with the Capacitor Wizard (so, not open, not closed and low ESR).

I've uploaded some pictures.

C2060 Test.jpg S8050 Test.jpg Fast-Forward-Schematic-Detail.jpg Q529, Q530, Q531 Voltages at Collector Depending on Mode.jpg S8050 and C2060.jpg Swapped and New Transistor.jpg

Remember, in that last picture, the top transistor is the replacement; but that's actually for rewind. I had swapped the original transistors to see if the problem travelled, and it did. So, rather than return the old rewind transistor to its original position, I just installed the substitute (easier board location, since I had to cross-over the base/collector).

I won't be convinced this has solved the problem until I've seen the unit operate for a few weeks (it gets daily use).

Again, I welcome comments of all sorts, even if you think I've missed something. My electronics repair training is from the 1970s, so who knows what the other folks on this blog might have run into that could help me with these units.
 
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