Pioneer SX-626 control amp transistors

I have an SX-626 that I acquired a couple of years ago. It has slowly developed noise in the right channel. I tracked the problem down to the control amp. After a recap of the control and eq amps, the problem persisted. So I looked to the transistors, expecting Q3 to be the culprit. I swapped Q3 and Q4, no change. Swapped Q5 and Q6, the noise moved to the left channel. Q5 and Q6 are 2SC1344. The manual also shows 2SC1312 can be used. I've gone thru many of the posts here and have found this listed as a replacement: ksc1845 512-KSC1845EBU (from Mouser), but they appear to be unavailable. I've been researching and it looks like this may work: 512-BC184. I am not an expert when it comes to transistors and I could use a little guidance.

This is my first post here, but I've been reading thru this site for a couple of years now. I've never had to post a question before because I've always been able to find the answers here. The level of knowledge here is just unbelievable. I've acquired a handful of other vintage pieces over the past couple years and this is always my first stop when trying to evaluate a piece.

Even if I don't get an answer on this question, many thanks to everyone who has helped me over the past couple of years without knowing it. The assistance has been invaluable.

Welcome to AK..I'd go with the 512-KSC1845PTA's from Mouser. EBU's thats and old list..There no longer available, FTA's are next best- but there on order.

avionic said:

Welcome to AK..I'd go with the 512-KSC1845PTA's from Mouser. EBU's thats and old list..There no longer available, FTA's are next best- but there on order.

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Thanks for the guidance and the welcome, Avionic. I appreciate it. Hopefully I can get this 626 running nice and quiet again. I tried to go back to a 90's vintage Pioneer while the 626 is out of commission, but I just couldn't stomach the sound. Found a Kenwood KR-3130 to fill in. I like it a lot, especially the tuner, but there is just something about the 626 that I really miss.

Make sure you are using the CORRECT VERSION of the Service Manual. There is a 1971 and a 1973 Version. http://www.kallhovde.com/pioneer/Pioneer/Main scan page.html they are both linked from this page.

replace any 2sa725/2sa726 with 512-ksa992fbu and any 2sc1451 with 512-KSC2310YBU.
These get noisy and are problematic in the PIONEER's.

Larry


Larry

Larry: an update:

2sc1451 >> ksc2310 old choice, heat problems
2sc1451 >> ksc3503 much better new choice, plus 2310 is fading away and soon will be nla....

512-KSC2310YBU TO-92 ecb 150v .05a .8w 100mhz 40-240hfe $0.11 ea :scheduled for obsolescence, look up ksc2310 in mouser - it'll make you sick...


so use:
512-KSC3503dstu npn to-126 ecb 300v .1a 1.2/7w 150mhz 40-320hfe $0.28 ea
just for grins and giggles - here's it's complement as well:
512-KSA1381estu pnp to-126 ecb 300v .1a 1.2/7w 150mhz 40-320hfe $0.27 ea

Thanks Larry and Mark for chiming in. I appreciate all of the valuable info. And yes, I have been using the correct manual. I learned about the two different versions here on AK, but thanks for looking out for me.

So, to be sure I've got this right:

2SC1312/2SC1344 > use 512-KSC1845PTA

2SA725/2SA726 > use 512-ksa992fbu

2SC1451 > use 512-KSC3503dstu


I know to be careful about ecb leads. Anything else I'm missing?

I received the new transistors and set about installing them yesterday. Replaced the 725's with 992's and the 1344's with 1845's on the control amp board. Everything went like clockwork, the noise I was experiencing from the one bad transistor was gone. So I moved to the eq board and replaced the 4 1312's with 1845's. I tested each step of the way and everything seemed to be fine.

However, after all four were replaced I discovered that I had no sound from AM, FM, Phono and Mic inputs. Aux and Tape positions worked fine. I had been testing with the Aux input only. I rechecked all of the solder joints and rechecked ecb lead positions. I could find nothing wrong. Finally in desperation I reinstalled the original 1312's. Everything again worked normally. At this point I left well enough alone, put it back together and back in service.

Has anyone ever run into this type of situation before? I should have reinstalled the originals one at a time and tested after each one, but I didn't think about it at the time, I was just anxious to get it working again. Is it possible I just got one or more bad transistors? Or are these transistors just not an acceptable replacement for this application?

Regardless, I'm happy with the results thus far. I've noticed that I have to turn the volume up 2 or 3 notches higher than before. Never went above 10 o'clock for comfortable listening before. Now I can go up to 12 or 1 o'clock. However, the signal is much cleaner and there is less distortion, even at higher levels. I have yet to recap the main amp. I got a little gun shy after the eq board incident. Now I'm wondering if there is more improvement to be had. I have the parts, so I'll give it some time and revisit it in the future.

Again, my thanks to those who helped directly here in this thread and indirectly in the countless other threads on AK. It has all been very helpful and made my first recap at least a partial success.

6 ways to install a transistor only one will be correct. Check the datasheets for the 1845 and the 1312's. It's very possible that the lead basing is DIFFERENT!

I checked, double-checked and triple-checked, before and after. Had printouts of the data sheets and the service manual with me while I did the work and I verified the ecb positions on the board. And I installed 2 new 1845's on the control board, so the ecb positions as shown in the data sheets and manual must be correct. I concede, even with all that it's still possible I screwed up on one or more of them, but it's unlikely.

At some point I'll take another crack at it and verify each step of the way and see if I can determine where things went wrong.

one has to remember that even the service manual is subject to error. and for the 725 / 726 / 1312 / 1313 transistors they were more often wrong than right.

ksa992 and ksc1845 are ecb
2sa725, 2sa726 very common to have errors on these, BCE, really!!!
2sc1312, 2sc1313 bce...

and I don't depend upon documentation (although I start with it), I verify EACH and every transistor's functionality before installation. There ARE testers that can take a randomly inserted transistor and identify each lead.