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Racal 1992

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Yoanndlc:
Hi,

I had a hold racal 1992 and I had some trouble.
When I connect the ext 10Mhz ref on channel A, I have a good reading during 20 second and it start to give bad frequency.

I checked the ext 10Mhz and it is stable.

I checked all the power supply and they are ok.

I see that the temperature of IC39 is around 65°C.
If you have a 1992, did you observe the same temperature on this device?

I did the Fault Finding Flowchart, and I begin to have an issue at fig 7.5.

If you had the same issue, I am very interested because I spend 6h and I do not see where it is coming

Thanks in advance

Yoann

Andy Watson:
U39 is an ECL ASIC - it runs very hot.

I have a vague (>25 years ago!)  recollection of a similar problem with a 1991. It would operate correctly for 5-10 minutes after power-up. After a while the channel wouldd become increasingly insensitive. The problem was traced to the potentiometer that sets the hysterisis on the channel comparator (R149 - channel A, R150 channel B). There was an internal short within the potentiometer. After a while it would heat-up and move the hysteresis voltage.

Yoanndlc:
Thank you Andy,

I will check the potentiometer.

I also read on the forum that the IC socket could also be a problem. During my tests, I used contact cleaner, and it worked better for a few minutes.

I will try to change the socket

coromonadalix:
be very careful with the chip, it is unobtanium if i recall


you had the regulators on the frame who sometimes become intermittent, they are under mechanical stress and they sometime break

shabaz:
I have an even older one of their counters. The IC sockets become unreliable for the unobtainable chips as others have found too.

The legs on some of those ICs are so weak, they can get damaged even when taking care lifting out of the socket. I didn't trust myself to insert it into a brand new socket, so in the end I permanently soldered it in.

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