stylus heat issue - power supply - VMS 70

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stylus heat issue - power supply - VMS 70

Unread postby prof msg » Tue Jun 21, 2016 7:19 pm

Hi,
Perhaps one of you has experience with a stylus heat issue on a VMS 70 / SX 74

The meter shows no current and the cut shows no heat. I tried more than one stylus, and checked continuity on each. I took out the the TE 66 panel and checked the connections to pot, meter, socket. I tried bypassing the meter, and then tried putting a multimeter inline in place. In all cases I measure 0 current when the head is in the down position but I see a little blip in the current meter as the head engages and again as it disengages. I also see a dip in the electrical depth meter as the head engages/disengages. Voltage across pins 23 and 30 on the NG 66 H card is 4.5 volts with the depth engaged(START), but drops to less than 1V when the head drops. My electronics knowledge is limited, but I'm guessing this is a power supply issue, possibly a voltage or current limiter.

Any ideas? thanks,
-Kevin
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Re: stylus heat issue - power supply - VMS 70

Unread postby smithadamm » Thu Jun 23, 2016 11:20 pm

You are right, it could certainly be a bad regulator. I would take a hard look at the large filter caps in whatever power supply provides power to the heater. I would also check any tantalum caps that might be in the psu.
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Re: stylus heat issue - power supply - VMS 70

Unread postby jjgolden » Fri Jun 24, 2016 12:40 pm

Have you checked the fuse on the NG66H1 card (far left)

JJG
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Re: stylus heat issue - power supply - VMS 70

Unread postby prof msg » Mon Jun 27, 2016 11:17 pm

Thanks for the tips,
There were a few things wrong with the fuse housings that were causing intermittency, not on the card itself, but on the panel to the right. It all works again.

-kp
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