Hello,
This is my first post here, thanks for allowing me in. I've had the chance to pick up an HP3403C True RMS voltmeter, serial 1452A03359, with options 0011 (Autoranging) and 006 (dB display).
I bought it with its condition unknown. I know some of the parts inside are absolutely not replaceable but for the price it was a bet I wanted to make.
?
So it came in the mail. It must have spent the last few years of its existence in a cellar as it had some slight facia corrosion damage, and absolute STINKS of mold. I have cleaned it thoroughly but it still smells a bit inside.??
The display is stuck on displaying +1V, blinking. If I set the speed to fast it blinks a bit faster. Sometimes it'll display rubbish until the next power off/on again. It seems to react to the switches as the comma moves with the ranges and the dB display also lights up. I have checked the power supply lines (following the procedure), they're good and I can't see much ripple on my oscillo. I'll replace the capacitors of the power supply but only when I know it works as to avoid unnecessary spending.
I have removed all the boards in it (converter and options) only leaving the motherboard, PSU and the display unit and it is still stuck. I therefore believe the issue is not converter related but display related. The display is basically a 3.1/2 digit DVM built around a LD110 (digital processor), LD111 (analog processor) and an SN74LS47N decoder for the displays. , and
?
I'm quite the beginner and lack some diagnostics knowledge. The display is also a rather convoluted assembly. Considering the high humidity storage it went through I suppose solder corrosion is not out of the question. I have already cleaned what I could (the boards were all perfect thought) and the gold plated connectors (also perfect) with isoprop.?
What would be your recommendations on what to try next?
Thanks everyone,
Arnaud.
?
