The HP 8600A Problem has Returned

[Kevin Kuehn]

It looks to me like the tab should be pin 10, because pins 7 and 8 should have the unregulated DC input on them.

[Chris K]

Those are just arbitrary numbers I put on the pins starting at one at near 12 o’clock. They aren’t labeled as you would count them on the transistor. It continued to work fine. What typically happens with this is there’s really no resolution and I button it back up, it works for a while and then starts with issues again. I think what I’m going to try is to mount a small cooling fan on the side blowing into the cabinet. If heat buildup is the issue, maybe that’ll solve it. I am going to replace the resistor with a new 1% 0.56 ohm wire wound resistor as it is supposed to have. As long as I have it open I’ll replace it.

[Chris K]

Buttoned it up...put it back on the shelf, just waiting for the fan. this morning I came down to the shop and turned it on along with the 8601 and this is what greeted me on the display.



All voltages were fine. I'm just about done with this. I pulled out the counter board, the one with all the IC chips on it. It has lots of replacements. This board (and no doubt this machine) looks like it drove someone nuts in the past just as much as me. When I put this board back in place, It started working.



This is typical for this instrument. Days and days of normal operation...it gets put in service and bang...it stops working. It's just a turkey. I think I'll sell it as non working and wait for another to come up for sale.

[kf4rca]

Corroded edge card connectors. I seen that problem in broadcast equipment as well, particularly at stations down on the coast.
But shouldn't this thread be in the Test equipment forum?

[Chris K]

Probably but by extension, this instrument issue is connected to, and an extension of, a restoration thread on the alignment of an RCA KCS28 chassis TV that went on for months and months. The issues with this instrument came to dominate the thread and I began this one here because I imagined the same folks involved in the original thread would be interested in the update.

[Kevin Kuehn]

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.

[Chris K]

Originally Posted by Kevin Kuehn

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?

[Kevin Kuehn]

Originally Posted by Chris K

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.

[Chris K]

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.

[Kevin Kuehn]

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

[Chris K]

Originally Posted by Kevin Kuehn

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.

[Yamamaya42]

Originally Posted by Chris K

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.

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

[Penthode]

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.

[Chris K]

Originally Posted by Penthode

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?

[Kevin Kuehn]

Here's a video of an LED version.

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