David Woolley wrote:
I've assembled the control board (and most of the front panel. In
doing the control board resistance checks I've got an apparently out of
range value for the 8A value. With R1 at the low resistance end of the
track, it is 2k72, which is below the minimum of 3k0, in the manual.
With R1 at the high resistance limit, it is 3k5. Do I have a problem?
I *did* have a problem that was indicated by this; even though I thought
I had carefully checked, I mixed up the 5 and 8 volt regulators. I've
switched them over now, and apart from losing some of the through hole
plating, it seems OK, with a couple of minor reservations.
In the hope that it will help someone searching in the future, the
symptoms, on powering up, were:
- All the segments on the display showed to some extent from all
angles and dominated the proper display when viewed from above
the horizontal.
- When the power supply voltage was above, approximately, the 8V
regulator drop out, it kept sensing slight changes in the pots,
so the display kept going to various parameter mode change displays.
- The current draw, measured externally, was around 220mA.
- Nothing on the control board seemed to be running warm, but there
were indications that something on the front panel, near the centre,
was, although not really hot.
- The internal voltmeter, was showing about 5V when the external supply
was turned down (I presume this is because it was using the the
nominal 5V as the reference, which was actually just was close to
the supply voltage, as the 8V regulator in the 5V supply had dropped
out.
- No segments lit on the bargraph.
The slight reservations are that the AGC threshold calibration voltage
only reaches 3.79, with R1 on the end stop and the current sense test
showed 0.14 amps (0.08 to 0.22) difference most of the time, with the
odd excursion to 0.16, compared with the manual figures of 0.16 to 0.18.
--
David Woolley
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