I picked this 410C up last year. It's missing the AC probe and the DC wasn't working. Ohms is fine though.
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It's very, very well made. Gold plating, orange drops, etc.
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Cool neon optical choppers glowing.
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This 89M Victoreen glass encapsulated resistor has broken. Seems to be OK though. I suspect a replacement will be difficult to find.
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Thanks to this advice from Findm-Keepm, I quickly discovered the DC test lead had broken!

The 410C manual is everywhere - and free - Agilent and BAMA both have them.

As for the DC, always ensure your probe has the requisite 1 Meg resistor in it. It's R1 in the manual. The ohms lead is a straight lead.

If the AC probe is missing, a 22 meg resistor, 2 caps (2600pf and 250 pf), and a couple 1N4937's in series (for increased PIV) and you're back in business. Lemme know if you need a 22 Meg resistor - I've got a few Carbon Comp ones, although a 1% 1/2W film type would be best. I built one to try out the concept, but we never used it, as I potted everything and threw off the frequency response at low voltages. Don't pot it and you're okay....

Cheers,

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I fixed it and it's work great now. Here I'm measuring 4.5 volts. It's dead on :banana:
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I'll try to scrounge up some parts and make an AC probe as suggested.

I made up an AC probe and it seems to be working, but I can't quite red the meter to zero on the AC ranges. It's especially bad at the lower ranges.

I've tried adjusting both the front panel AC Zero knob and the internal trimmer. I have them both at their extremes and it's not quite enough. I checked the associated resistors and replaced a 15K that had drifted a bit and it didn't help.

I'll keep digging...

OK, I'm admitting defeat for now :( I just can't get it to zero properly on the AC range.
Besides, I don't measure AC that often and can use other meters if I do need to.

I took another whack at it tonight and it seems to be working :)

Here's the AC Zero circuit. What I did was short out that 15K resistor and rotate the control all the way over. Effectively, grounding the end of the 56M resistor.
Actually, I did temporarily directly ground the resistor and it had the same effect, but I want to preserve the control action in case I did need it at some point.

That brought the needle down to 0 on every AZ range.

What I found confusing was why did the AC range need a special Zeroing control at all ?
I figure maybe the original EA53 diode tube introduced some offset and this control nullified it ?

I see that the tubedepot list price for a EA53 is $99.95 (http://www.tubedepot.com/nos-ea53.html) each :yikes:

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At any rate, I rigged up a crude probe with a 1N4007 diode, fed in some AC and compared it to my digital scopes RMS reading. I can get them to agree fairly well.

That leaves picking up some better HF diodes and making up a real probe. A trip to the hardware store turned up these parts.
I'll cut the tube down a bit shorter and stuff the four components inside. I'll solder a short ground wire and clip right to the tube.

I figure I can drill a hole in the end cap for the coax and a hole in the other end for a probe needle.
I'll put some teflon or PVC tubing around the probed need so it doesn't short to the copper tube.

Perhaps I'll put some heatshrink tubing over the probe body or clear coat it so it's not shorting out everything it makes contact with.
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There are EICO and Heathkit probes up on eBay all the time - the demodulator probes that came with the EICO 145 and 147/147A work well in this application - the body is aluminum with an acrylic threaded insert at the probe tip. You can then use perfboard to mount the detector and the R-C network.

I snatched up enough probes on the 'bay to outfit my three signal tracers (one Heath, two Eicos) and one in reserrve to restore my RCA WV-77.

Perhaps someone in the forum or over on AK might have a demod probe they'd be willing to let loose. Else, search for Eico, Heath, RCA, Knight, or other "vintage" probe on eBay. Heck, even some of the newer round-style logic probes can be gutted for a probe body and tip.

Cheers,

I didn't come across any vintage probes to re-purpose so I went ahead and made my own.
I used the end of a mechanical pencil for the probe tip. It's a little crude, but seems to work fine :)

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Nice meter and nice job!
Used to calibrate/repair them 30 years ago in the Army.
Most of the repairs were the probe tube, or the choppers.
Used to raise hell getting some to pass the 100Mhz frequency response test. Our QA inspectors knew this, so we got them out of the shop ASAP!