I acquired a Heathkit IM-4100 an assembly manual, and update notices. It looks like it was expertly assembled. I haven't dealt with any modern equipment before, with those newfangled transistors and such, so I feel like I'm starting from scratch.

My first issue: Should I replace the 6000uF/15v aluminum electrolytic? It looks healthy, of course, but it's about 37 years and 8 months old.

It has a slow-blow fuse that's intact, but it looks a little funky--the white stuff inside the fuse looks like it doesn't belong there. Replace it? Cost is maybe $3.00.

https://lh4.googleusercontent.com/-aWSFSwkSNig/U1iao2c0HZI/AAAAAAAAMrU/37y4MqFNI_w/s500/Heathkit%2520IM-4100%2520501.jpg

There's also some dark discoloration in one area around some diodes, to the left of the fuse in this photo:

https://lh6.googleusercontent.com/-H6nUzcoGtn8/U1iaoAOxj2I/AAAAAAAAMrM/WY1_hHZ06tg/s500/Heathkit%2520IM-4100%2520500.jpg

The same area from the other side of the circuit board:

https://lh6.googleusercontent.com/-DEilI_G2YIY/U1iotByZgLI/AAAAAAAAMr0/SjlFLX8yCz8/s500/Heathkit%2520IM-4100%2520504.jpg

Is this just from a lot of rosin, or could it be from excess heat?

Last question: I anticipated needing a BNC-to-BNC cable, so I cobbled one together with junk-box connectors and video cable. Is this going to be adequate for what I'm going to be doing with RF signals?

https://lh4.googleusercontent.com/-zCg6JGKxsJk/U1iapw_kyjI/AAAAAAAAMrc/VqKFbfWp30A/s500/Heathkit%2520IM-4100%2520502.jpg

I appreciate any advice I can get. If I can get these issues settled, then I'll look into calibration.

The white stuff inside the fuse is probably flux residue. No need to replace it.

The electrolytic is a judgement call. No sign of leakage that I can see. A new one wouldn't hurt, but it isn't likely to fail catastrophically during initial testing like a filter cap in really old tube gear.

The diodes probably run hot enough to bake the board a bit. If you replace them, leave the leads a bit longer and space the diodes off from the board by 1/4" or so so air can get under them. Replacements are cheap enough, but be careful desoldering them. The heat damage to the board will make the traces more fragile than normal.

Your homemade cable should be fine. The max frequency on this thing is only 100 MHz, no?

Thanks. Max frequency is 30MHz. Having no experience with circuit board soldering, I'll leave everything alone for now. Next time I discard an electronic whatever, I'll keep some circuit boards to practice on.

I just got a new counter too! Mine is HP 5328A with the oven and 512 MHz options. Fantastic! Google it and check the specs; it's awesome. Now to figure out what to do with my old HP 5245L units and plugins.

I love test equipment. Recently also acquired HP 3456A voltmeter as well, reads volts and Ohms to six digits. Everyone needs this.