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Author Topic: Technics RS 1500 Speed Problem  (Read 5073 times)

Offline endlandmusic

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Technics RS 1500 Speed Problem
« on: January 16, 2013, 08:14:09 PM »
Hello
I have the following problem with a RS 1500:
After switching on the machine, it needs about 8-12 minutes to accelerate to the right playback speed. It always starts about 10% below the exact speed. There is no difference, if the variable speed is switched on or off, the pitch range remains the same; too slow.
I cleaned the switches and contacts, followed the alignment procedure, reseated the capstan control board, checked the connectors.
The tape path is clean and the reel tensions are fine too. After switching the machine off and on, the same procedure happens again. I checked all the diodes and changed all electrolyte capacitors on the capstan control board, nothing changed...
I have another excellent working 1500 and a 1700. Before I'll try out to change some parts of these working machines into the 1500 to locate the error, I'll be glad, if someone has an advice or experienced the same problem.
Greetings from Studer-Nation, Switzerland
Jens

Studer A-80 RC MK IV, Studer B-67 MK II, Revox C-270, Technics RS-1500/RS-1700, ASC-6000T/6002, Tandberg TD-20A-SE, TEAC X-2000M, Braun TG-1000, Uher SG 561 logic.

Offline ironbut

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Re: Technics RS 1500 Speed Problem
« Reply #1 on: January 17, 2013, 01:37:17 PM »
Hi Jens,

Welcome to the forum.
I'm guessing that you have the service manuals? If so, you should check the voltages on the power supply board. It could be a bad cap on that board.
Another question,.. does this problem occur at all three speeds? If not, you can try bypassing the speed switch to see if that's the source of the problem (could be a bad switch).
Also, try increasing the pressure of the pinch rollers a little. You can do that by inserting an allen wrench into the screw head that holds the rollers on and applying some pressure toward the capstan. You're just checking to be sure that the tape isn't slipping.
Another issue that I've seen. One of the IC's on the capstan control board may have gone bad (don't ask me how but it does). Since you have another 1500, you could switch capstan control boards and see if it works. Since you've replaced all the electrolytics already, if the different board works okay, it's probably one of the 3 IC's.
It's easiest just to change them out.
Unfortunately, those IC's are long out of production but I've found some sources in China that still have the stock parts.
So, if you get to this point and think it's the IC's, give me a PM.
steve koto
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Offline docb

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Re: Technics RS 1500 Speed Problem
« Reply #2 on: January 17, 2013, 07:07:22 PM »
Yeah, I would be inclined to recap the power supply.
Dan "Doc B." Schmalle
President for Life, Bottlehead Corp.
Managing Director - retired, The Tape Project

Offline endlandmusic

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Re: Technics RS 1500 Speed Problem
« Reply #3 on: February 13, 2013, 06:07:36 PM »
Hello,
first of all I'd like to thank you for your advice.
Finally I fixed the problem. The problem was somewhere in the ICs.
I changed the whole board with a replacement part. I works fine again.
I started to recap the whole machine then. In fact the overall audio quality, especially the s-n ratio increased. I measured 74db !!! ( Aligned to SM 900 with 15ips ) it really now sounds close to my Studer B-67 and the ASC 6002.
Love the Technics. Looking forward to get a 1520 and a 10A2 ( nearly impossible to find here in Europe ).
Kind regards,
Cheers
Jens