When someone has done poor re-work like that on a two sided circuit board, there's no telling what they did to the feedthroughs when they removed the IC's. Board needs a thorough cleaning and inspection. Make sure the IC pins are soldered both top and bottom wherever traces feed between sides. Besides the edge connector, the socket it plugs into needs to be cleaned. There could be a film of solder flux on some of those areas. I use lacquer thinner to carefully clean the flux off. Beware lacquer thinner can melt some plastics.

What about denatured alcohol Kevin?

Usually works on fresh rosin based flux. But as it ages it's harder to remove. It appears a paste flux was applied to some of that. And it sure looks like there's a corrosive thing going on with the gray or blackening in some areas. Acetone is another solvent that will remove flux.

OK...I'll do a rehab on the board and see what that does. I think that'll be it for this piece. I'll just wait for another to come along.

I thought you had two of these, but maybe I'm confused with some other test gear.

I have the complimentary sweep generator. The 8600 and 8601 generator are a matched set and really cannot be used to do alignments with other equipment. I did have to go through 2 8601 generators before I got one that worked. Like I said, these 2 pieces of equipment have been very very challenging to my mental health. :screwy::screwy::screwy::screwy::screwy:

:D

https://www.google.com/url?sa=t&sour...Qm9SJjvreiAQW9

Sorry Chris that you ended up with a dud 8600a. I was luckier with mine. I have used it now for over 20 years and the only problem I had was a broken marker push button.

If you go for another, keep your eyes out for the later version which uses the 8 segment led displays. I believe that will prove more reliable.

Thank you my friend. I was not aware there was another version of this with led displays. Do you know if it happens to be the same model number?

Here's a video of an LED version.

https://www.youtube.com/watch?v=ZHUJa2NbTgc

Model number is still 8600A. It's a production run change

I'll give ya $5,000 for it! :yippy:

Just kidding of course...well kinda'

Who me? Sorry, I don't have one. I just noticed the LED version is the same model.

Ahhhhh. Got it

Started working on the cleanup of the counter circuit board. 90% isopropyl is working well removing the old dried flux residue. I've ordered NOS original Texas Instruments ICs and I'll be replacing the suspect chips soon. I'll post pictures of the board when it's done. Of course, I'm hoping this solves the issue once and for all!!!

The best solvent for flux residue is a 50-50 mix of denatured alcohol and "xylol" from the paint dept of Menard's or Lowe's etc. "Xylol" is actually the hydrocarbon xylene (mixed isomers),

Hopeful is good, but don't rule out the possibility of more than one issue. It's hard to know if the display lockup is being caused by the low 5v supply, or a symptom of.

Oh yes I have put this piece of equipment in the “lemme see if there’s anything else I can do” category while I continue to look for another one. The 5V freezing display problem was accompanied by the return of the crazy frequency jumping on the display. In other words both of the original symptoms have returned now that I’ve had it in use again for a significant amount of time. I have little hope for this fix Kevin and the way the piece has tortured me in the past, I’ll cleanup the board, replace the suspect ICs, put it in service, declare it’s been working reliably for weeks…and then it’ll act up again. The guy I bought the sweep generator from has offered to fix it and his skill set indicates he’d be successful so there’s always that route. Just want to exhaust what I’m capable of doing before I spend a couple hundred dollars more on repairs and shipping.

In spite of the freezing and jumping display, It's too bad we didn't get to the bottom of the sagging 5 volt power supply. The flux mess on the display board is something that's good to clean up regardless if it fixes anything.

Looks like it’s working fine after the cleanup. I’ve had it on for short and long timeframes over the past 5 days and no issues. Gonna do some endurance and accuracy tests over the next month or so before I’ll be confident the fix is completed

Failed again. Frequency readout on CW Counter freezing with the same low 5V issue however, if I switch the instrument to scope with the generator in CW/no sweep, it reads the frequency perfectly. Tracks with it just fine and stable. WTH?

It's fixed it's fixed it's fixed!!!!!!!!!!!!!!!!!!
 

A little reading saves months of stupidity. I read through fault modes in the service manual in particular, the ones specific to the regulator board and I'm embarrassed to say all of this was caused by a bad 2N3055. Freezing the regulator 723 simply broadened its regulation range so it was able to pull it in to 5V despite the 3055 being bad. It is rock solid 5.000V DC on my DMM and has been that way for days. I wanted to be sure before I posted. Pretty darn happy and pretty damn embarrassed I'll say.

Thanks everyone for the tremendous support. Now I'll get back to that gosh darn RCA!!!