Better than the Fiat I drive!
When I first opened this up and saw the level of corrosion I thought I'd been sold a pup after all as there was no way this was going to work like that, both batteries were spent but seller stated it was working so I assume that it was working at the time when he checked back in 2017 when he first tried to sell it.
Anyway, batteries were tossed away, terminals were suitably cleaned and the "D" cell spring contact removed and worked on to restore bright metal again and reassembled, new batteries fitted and nothing not a dammed sausage, not even a flicker of the needle. Out came my 3466A and checked the circuit through, volts etc all checked out OK until I came to ohms adjust pot, open circuit, detoxed it and it did show some signs of life but boy was it finicky, detoxed it a few times and worked the pot well each time and eventually it did come good and I was able to adjust the ohms adj to get a zero reading on the ohms scales. We were in business, meter seems to be slightly sticky and the meter has a poor linearity across the scales, as does its sister V-7AU valve voltmeter. I'm hoping that as it seems the meter has been in a damp atmosphere that as it fully dries out that the meter might become more fluid in its movement and settle on its value correctly rather as it is now, sometimes having to overshoot the value and drop back slightly to correctly read the meters input.
Accuracy of the meter is at best an indication of the value when compared to todays digital meters.
Phew I hate it when you get stuff that doesn't work properly to start with. That gulp, that moment of frustration etc. Good that it's working better now. I found, via another web site, that the meters are often sticky from static. If you rub a tiny bit of washing up liquid all over the front of the meter face (not the inside!) it neutralises the charge and they don't stick. Odd but it works.
Nice looking bit of kit. I really wish they sold stuff like that now.
On to a slightly newer bit of Heathkit equipment, some photos of the IM-5238 AC voltmeter. Did some work on the power supply this afternoon. Mostly eviscerating it. There was nothing going on via radio so bugger it, chop chop time.
First some photos of the insides before I got at it. The bottom right side of the unit is the power supply which is shot. Both regulators are shorted, there's a diode gone, drifted resistors and the caps are shot too. Note the ancient 78/79MG
wankers regulators.
Also discovered the transformer was knackered. One of the taps had come off and the thing smelled bad. Out it went. The entire mains side of the unit has been stripped out. I will add a new transformer, IEC socket and fuse holder. The voltage selector will be blanked off. If anyone wants to change it they can get the soldering iron out
Big hole where it was. RS will deliver me a new transformer on Tuesday. In the mean time I'll do the panel mods to add the fuse holder and the IEC socket.
Now for the power supply. Out it goes, into a pile of junk:
Not too bad looking now!
In goes the new power supply. This is a pretty standard LM317/LM337 dual rail supply with bridge rectifier. Setting resistors were 240 ohms and 3.6K which gives you around 20.1 volts. The manual specifies 20 volts within 20% so I'm doing better than they are. Protection diodes are badly soldered to the other side of the board. One half of the regulator was built up on a breadboard and loaded with 60mA of sink at 20v with 32V in on the regulators. This is 20mA over the rated current so the heatsinks were checked after an hour to make sure they weren't too hot:
Money shot. On the function generator. Pretty accurate so far. Within 2-3% and I haven't done cal on it. The power supply was the only dead thing and it didn't kill anything else. Miracle.
Next time, new mains inlet, transformer and calibration hopefully. Oh and re-cap the rest of it before another one goes phut.