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Author Topic: Technics 1500 board problem  (Read 2205 times)

Offline Gkar

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Technics 1500 board problem
« on: November 07, 2011, 09:13:13 PM »
howdy, all.  I finally started up my 1500 recap project, this machine is very clean with virtually no head wear.  I have noticed a couple of caps having green goo on the legs, which is the electrolyte leaking from the cap onto the leads and corroding them.  Have done a recap of a 909, and that went well.  However, I have run into a bit of a problem on this machine insofar as the schematic/service manual does not quite match up to the boards I have in my machine.  In particular, the reel motor tension control board (which had a leaky cap, but I am replacing all) basically is mirrored from one side to the other on the ends, with matching caps, transistors, resistors.  The board number on my machine is marked ELNA 94V-0, on the service manual I have its 94V-1. The problem is that cap C813, which I pulled, was marked 50V1ufd, it's match, C814 on the opposite side is a 16V10ufd.  The circuitry the cap is in is the same on both ends, which makes me suspect a bad stuff when the board was made, and I have been having reel motor problems...  of course, that was more likely the leaky cap, but who knows.  On the schematic of board 94V-1, those same caps are the same value, however, that value is 16V33mfd, same transistors and resistors, but the cap values are different.  So, does anyone have a print of board 94V-0 and have the value for C813?  As I noted, I suspect a bad stuff, and that the cap should be a 16V10mfd, not the 50V1mfd I found...  thanks!
"Music possesses far richer means of expression, and it is a more subtle medium in which to translate the thousand shifting moments in the mood of a soul." - Tchaikovsky

Offline ironbut

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Re: Technics 1500 board problem
« Reply #1 on: November 08, 2011, 12:29:28 AM »
Hey Randy,

There are at least 2 versions of the boards in the RS1500. The quick way to tell the two (I know of) apart is that some have a small circuit board with the oscillator and an IC attached to the frame and wired to the main control board. The other version has all three of the IC's mounted on the main control board. One of these IC's is actually different (the one on the small board).
When I've recapped these machines I've noticed that the ones with the small circuit board (I suspect that this is the version you have) do deviate from the service manual in some small ways. The tension board is downstream of the different IC so I would imagine that that's why the value differs from the schematic. I highly doubt that there would be a different size cap between C813 and C814 but of course, it's possible.
I seriously doubt that there's a different version of the service manual for these 1500's but my WAG is that the change of boards were the result of other models such as the 1520 (or maybe even the 1700) whose circuit board layout is different from the original 1500 (as in the service manual). So, perhaps the schematics/part lists for the 1520 or 1700 is more in line with these machines.
BTW These service manuals are very rare!

I've always replaced the caps with the same values as the ones that were in the machine when I got it.
I would suggest that you give Jeff Jacobs at Jcorder a call or email and ask him. He's probably taken more of these machines apart than anybody (at least to the board level).

http://www.j-corder.com/

Failing advice from Jeff, I'd replace the caps with the values that were in there,.. unless it looks like someones been fooling around in there (different brands of caps, bad soldering etc.).
steve koto
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Offline Gkar

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Re: Technics 1500 board problem
« Reply #2 on: November 08, 2011, 01:36:37 PM »
thanks, Steve, I am guessing that C813 was put in wrong (stuffed) by mistake, and will go with the same value used on the opposite edge used, since it is the same circuitry, etc....
"Music possesses far richer means of expression, and it is a more subtle medium in which to translate the thousand shifting moments in the mood of a soul." - Tchaikovsky

Offline docb

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Re: Technics 1500 board problem
« Reply #3 on: November 08, 2011, 02:31:45 PM »
I don't have a clue what the proper part designation is, but I would suggest caution in replacing a bad cap rated for 50V with one rated for 16V.
Dan "Doc B." Schmalle
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