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Electronics => Repair => Topic started by: rhb on May 14, 2018, 02:34:56 pm

Title: Millivac MV-823B-S1 millivoltmeter repair
Post by: rhb on May 14, 2018, 02:34:56 pm
This is an early 80's USAF power meter with a diode sensor good to 1.5 GHz with a dynamic range of +30 dBm to -50 dBm.  I think it's probably OK except for needing adjustment and a new sensor capsule.  Millivac is still in business, but unfortunately, they want $75 for a service manual which raises the cost of repair a good bit.

I bought an HP 438A with an 8481D and an 8482A complete with calibration and data, so I don't need this.  The style of construction is such that I could easily gut it and just use the PS and front panel and case simply by removing the main board and wiring.  But it seems a shame to do that.

At present when powered on the needle jumps and then drifts off to zero.  Prior to application of tuner cleaner to the switches and reseating all the semiconductors, it drifted to the maximum reading.

If operational, it should serve very well for most ham radio uses.  I don't care about the value of my time, but I don't want to spend more money fixing it than I can sell it for when I'm done.  I'm guessing that it's worth $150-200 if calibrated and working properly.  So buyng a manual uses up half the repair budget.  If for some reason it's worth less, please let me know.   This was a flea market junk buy, so I know next to nothing about it.
Title: Re: Millivac MV-823B-S1 millivoltmeter repair
Post by: CarsonReidDavis on May 17, 2018, 03:50:01 pm
I poked around on Ebay for Millivac models similar to yours and didn't find a whole lot of sold listings. Weirdly, a ton of the results I did find were German.

Sold Listings

Have you exhausted your online search for digital manual copies? I found an 828A manual, which might be useful, although this model lacks the row of buttons on the right hand side. There are also some YouTube videos of people repairing this model.
https://forums.qrz.com/index.php?attachments/mv-828a-pdf.408609/ (https://forums.qrz.com/index.php?attachments/mv-828a-pdf.408609/)
Title: Re: Millivac MV-823B-S1 millivoltmeter repair
Post by: rhb on May 17, 2018, 06:29:01 pm
It appears that Millivac makes sure manuals are not available online.  They told me they were not and they needed a serial number to furnish the correct manual.

I'd found the  828A manual but it does not include schematics and contains very little useful information service information.  I've pretty much concluded that it's a nice case, analog meter and switches and that's about  it.

I have become acutely aware that there are many reasons for the high resale value of HPAK gear. Not the least is HPAK respect for the end user. I bought an Instek GPE-4323 linear power supply. They used regular linear pots to set the voltage and current.  It's got a 4 digit display, but it's damn near impossible to set a particular value to 3 digits.  If you get 4 it's purely an accident.  I asked for schematics.  NO.  I asked for at least the pot section.  What I got had no values for the resistors and then referenced numbered points.  Completely useless. I was going to patch in  trimmer pots. I'd like to put in a multiturn, but can't find any that will fit.  After spending a day on it, I'm buying another bench supply that says HPAK on the front.

After my experience with Rigol, Feeltech, Siglent and Goodwill Instek I doubt I will ever buy another piece of Chinese gear above the couple of bucks on eBay stuff.