Datron 1281 repair

[whatamidoing]

Hey

[pelule]

Posted by: whatamidoing
EDIT: the fast test also tests the references...just not 2134, you'd think that would help pinpoint but it doesn't, also the values I "caltrig'd" during the calibration procedure haven't been saved...for instance the 10V range was reading 10.000020, after quitting external calibration using the same source it's now reading 10.010809. Utter madness.

Hi whatamidoing,
I assume you have done a proper warm-up (powered for > 8 hours) before you did the cal.
So it may an issue with the NVRAM write enable circuitry. Means, even you have enabled CAL with the key, the WE of the NVRAM may not. Simple method to test: are you able to change the CAL-Date?
If not there may several reasons: the 5V, the power fail circuit, the ASIC or simply a contact issue at the NVRAM socket.
/PeLuLe

[Kleinstein]

"ratio reference error" would point towards the special transformer and surrounding circuit used to generate internal cal voltages to do the 10 V  - 1 V - 0.1 V adjustment step. This is kind of a very stable divider to generate a few internal test voltages used to check / measure the amplifier gain steps.

[TiN]

Could be also problem with switching/circuitry that compares REF1 to REF2, as if I remember correct second reference is just used for self-test purposes? Reference itself is two identical modules on the main analog board, that are based around LTZ1000 circuit.

[Mickle T.]

I also got this error on the first run of the 20 years uncalibrated Datron 1271. In case of Datron 1281 an error flag is being raised if REF1:REF2 ratio is drifted more than 20 ppm since last internal source calibration. If ISC was too long ago, just run it again.

[Mickle T.]

You can just enter to the cal mode and quit from it without any action, then runs ISC. If no other hardware problems, the error code must disappear.

[quarks]

Just in case you have not checked all electrolytic capacitors,
My suggestion is to make sure you do not miss one.
Also double check all powersupply voltages incl. ripple with oscilloscope.
Once I thought I checked all but unfortunately overlooked one little cap and several days of troubleshooting later I finally identified this sucker as the cause of all trouble.