Electronics > Repair

Datron 1030D RMS Voltmeter

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theHWcave:
Hi Chris, thanks for that image and the info how the 1030 evolved. I attach an image of the AD board with the resistors for the LED 7-segment displays.
I noticed that on you image of the older AD board, Q4 also has a solder blob on top. Any idea why they did that? Testing them for temperature drift?

Regards
Heinz

Gyro:
Hi Heinz,

Thanks for the A/D photo. Remembering now, I had a 1045 (DC voltmeter) in the same case format and the board looks very familiar (aside from the LED drivers). It is non-multiplexed so it has the same arrangement for the extra digit, 1 latch and 1 driver IC missing with associated resistors. The difference from the later ones is that they didn't solder in the sockets, test with the ICs populated, and then pull them out again on non-option models! A bit of a shame as it means that you do need access to the bottom of the board to fit them. First, you would need to check that the display board actually has the extra digit or at least the footprint and you can find a compatible display (not an issue on the panaplex ones because they were dual digit packages).

Yes, there is a Select-On-Test 'Factory Select Value' resistor trim for Q4 thermal matching (it's the dual JFET input stage), it's referenced on page 52 of the manual. The procedure includes a quick dab with a hot soldering iron on the package! Datron used a lot of 'SOT' 'FSV' resistor trimming during oven cycling and burn-in. The relevant resistors are raised on metal pin sockets to allow easy swapping and then soldered on completion. Being the 6th production board, it probably had the privilege of being performed, or supervised, by the designer, so is probably a rather well trimmed example.

I don't know if you noticed, but on my photo there is a second vertical brass screening strip, soldered further towards the rear of the RMS board, between the 3 SOT FSV resistors and the single trimmer cap (C24). It might be worth cutting something suitable and adding this (obviously being careful that it doesn't short the SOT FSV resistor pin sockets). They must have added it to improve performance (I think the circuit flow wraps back on itself in that area).

Regards,
Chris

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