Reed relays for Racal Dana 1991 or 1992 counter timer

David C. Partridge schrieb:

David, please allow one question: Did You connect the SDT OUTPUT to the right inputs for the test (to A for SF 77, to B for SF 78)?

Achim

I understand why you ask, and yes, I did connect the reference out to input A for test 77 and input B for test 78. I used a piece of coax 90cm in length.

Did You try snipped-for-privacy@racalinstruments.com? I found them very helpfull some years ago. But I'm not sure, if they are still alive... I ordered some parts from racalinst Germany, which took a lot of time. The parts itself were not very expensive, but they had a minimum order of 25 or 50¤. UK was a lot easier, but I was foced to order in Germany...

Achim

It's not the Channel A 50 Ohm/1M relay whatever SF77 tells me. All the channel A relays are switching and doing what they should when driven with the front panel controls.

Unfortunately, the manual doesn't say exactly what SF77 actually does - clearly it is more than just exercise the relays. What is notable is that the only relays that appear to be switching are the 50Ohm and x10 relays, but the other relays that are supposed to be switching in this test mode (DC, FILTER and COM A) do not appear to be being driven.

The STD out is 3.5Vpp with the baseline sat at 0V (i.e. varying DC, not strictly AC). Will count with 1M input / AC coupling

Switching in 50 Ohm termination drops this to about 1.3V pp and will still count.

Switching to DC coupling - stops counting.

Switching back to 1M termination - will count again but somewhat erratically.

SF78 for channel B doesn't seem to be doing much in terms of driving relays, though the front panel controls DO seem to work to actuate the channel B relays???

Dave

I've been doing some further checking - definitely something is sick around the A/B amp or the DAC (TEC) on the H2 hybrid.

Here's what I see:

SF76 (trigger DAC exerciser) gives sawtooth between 0 and -10V on channel A trigger level output, and pretty close to 0V on channel B trigger level output. It should be a sawtooth between +5.1 and -5.1V on both.

DC trigger levels:

For channel A using TRIG Level control for +5 seems to be at -9.3V, and for -5V drifting between -8.8V and -9.3V (where it eventually settles).

For channel B voltage does change but not very far from 0V (small number of mV).

D.

David C. Partridge schrieb:

Checked: both are here at +5 and -5 sawtooth.

Strange...

some ideas: check D.A.C +-11.2V (7,8 against 3,11) Check Powerless Resistance of D.A.C. 1,2 against ground... Check C84,C14,C108 (short?) What about IC25?

Achim

+/-11.2V rails are good. DAC pins 1 and 2 are 1.55M to ground. Caps are good. IC25 seems alive at least as far as putting a logic clip on it is concerned.

I think that I've got a sick H2 hybrid here. I'd like to think it was something else of course, as no doubt this is either unobtainable or very expensive.

D.