Datron 1065 Analog board fault?

[uslrs]

Hi All,
My Datron 1065 suddenly developed a fault on the Ohms ranges - now displays Error 6 (outside calibration tolerances).  This occurred after the leds on the ohms range buttons flashed on an off between 10K and 100K.  I'd previously replaced caps and regulators in the power supply and the unit had been recalibrated and was absolutely fine before this issue occurred.  I've rechecked and adjusted 5v and 15v supplies as per the manual but the Error 6 is still present and although the adjustment changed only approx 8mV on the 5v supply and about the same on the 15v supplies, I'm now getting Error 7 relating to the dc volts range in addition to the Error 6 when I run the units self test.  Any ideas where to start on the Analog board?
Many thanks.

[dacman]

I have experience with the 1062, and on it, if the power supplies are good, Error 6 (Ohms) is almost always due to a bad relay.

Check the blue electrolytic capacitors on the Analog PCB.  They are part of the +/- 42 Vdc Inverter (i.e., a power supply).

Please verify Error 7 is related to DCV on the 1065.  (For the 1062, Error 7 is an ACV error.)  If it is a DCV error, then that needs to be fixed first.  (If so, I'd suggest disabling the other functions, ACV and Ohms, during repair.)

Check the inputs to the +/- 15 V regulators.  There should be at least 2.1 Vdc more than the output worst case (when powered at the low end of the power line input voltage range).  If not, I'd suspect the bridge rectifier.  (This is a secondary check.)

Check the power that energizes each relay.

[uslrs]

Many thanks for that Dacman - you're right re Error 7 - it's an AC converter 1v range fault according to the test flowchart in the manual (incidentally, I've only got service/schematics manual for 1061/A/1062 - but the analog board seems very similar in most respects).  The Error 7 only occurred after I adjusted the 5v and +/-15v voltages, which are now within 1 or 2 mV of the values stated in the manual.  Could this adjustment have caused the Error 7?  I'll check the relay/ psu input votages as you recommend.  Thanks again for your help.

[dacman]

The adjustment should not have caused any errors.  I'd suspect something else.  If the +/- 15 Vdc supplies are on the edge of failing, they can test OK in DCV mode, but if loaded a little more when ACV or Ohms is selected, they can test bad (too much ripple).  Here in the USA, with 120 Vac mains power, I expect 20 Vdc at least into the regulators (so that they will work OK if mains power is near the lower limit).

Check C45 through C50 on the Analog PCB.  These have a high failure rate and can cause the errors.  I would recommend an impedance meter that can separate the impedance vectors so that they can be reliably tested in-circuit.  Since both Error 7 and Error 6 showed up at about the same time, I would highly suspect these capacitors.

All the relays can be tested with the unit powered on.  If they are the R10 style (clear plastic cover) then the cover can be removed and the contacts burnished.

Another problem on the 1062 is IC contact resistance.  I sometimes use DeoxIT on the contacts.