Hi,
I picked up a Fluke 97 this weekend, which was a great deal and a very welcome find. I'm looking forward to being able to use it as a portable scope for my hobby functions. The scope did not come with original probes, but the knurled BNC are insulated, so I should be in good shape with regard to 'hot' grounds (thank you EEVBlog postings for keying me in on that). And, the EL backlight is a bit dim, but I will deal with that later. The bigger issue for me is that AutoSet does not work properly.
I was looking at the YouTube "how to use" Fluke video on the 97 and I quickly noticed a problem. When I inject a (F97 internally generated) square wave, and press AutoSet, it works great. However, that is not always the behavior. Very often (and I haven't quite figured out the reproducible sequence), when I press AutoSet, I'll get more relay clicking than when things are working properly. From a display perspective, the scaling starts out nicely and then gets progressively smaller as the v/div increases. The process stops, of course, when the scope has reached is maximum deflection setting (or minimum, depending on how you look at it). It is as though there is a stuck button, which *may* be the case (see further in this posting). Once in this state, I get the same behavior each time I press AutoSet... Starts off looking great, more relay clicking, and the deflection gets smaller and smaller until I have basically a flatline (with some noise). It is worth noting that the increase/decrease deflection buttons seem to have no effect.
There are only two ways that I've noticed that seem to reliably get me out of this state. The first is to cycle the power. The second is to go to 'Meter' mode and then back to 'Scope' mode. I have further noticed that as soon as I press either the increase or decrease buttons for the deflection, I trigger the scenario (assuming that AutoSet is in the working state at that point). I've mulled over whether or not this means there could be a stuck button, but my sense is "no" because the pressing of the button does trigger some action, namely the undesired behavior. I have only experimented with the A channel, so I don't know if AutoSet works on the B channel yet.
I do have a little more information. Although this behavior existed prior to doing so, I am fully aware that the units are 30 years old and that electrolytic caps could be faulty; as such, I opened the unit up. Sure enough, one of the surface mount caps is leaking a little (not too bad). I'll be replacing all of the SMT caps. Hopefully this will make the EL a little brighter (?) and decrease the whine. Interestingly, one of the FOUR caps is missing... completely MIA. Based on the look of the solder on the pad, it looks as though the cap was rather rudely yanked from the board. It was not in the case floating around. I don't know the story on this, but I am wondering if it could be part of the problem. I don't have the scope open right now, but it was the cap that was on the far right of the "four" when looking at the scope in the normal position (top away from you). Although this might cause more noise, though, I can't really see how it could cause the problem I'm seeing, but I'm curious if someone has thoughts on the matter.
I have also wondered if I could have a corrupted OS. I have either 4.02 or 4.03 (again, don't have the scope in front of me right this second) as my firmware. I have read elsewhere on EEVBlog that it is possible to reload the OS, but I'm not sure if this will eliminate the calibration values which I'm reticent to do, even though the values probably are not all that good anyhow, given the age of the scope. I'm more worried about bricking the whole scope. Further, I don't presently have an RS232 IR interface for the scope. If there is a way to get a checksum on the firmware, however, that I can verify against someone else's values, that would be a good way of figuring out if corrupted code is the problem (unless the checksum included the calibration data).
Well, that is about it... I'm hoping that someone out there has an idea as to what can be causing the problem. If you do, I am all ears! I'd love to get this working again as I have lots of places I can use it.
Thanks!
Alan
P.S. Outside of the electrolytic SMT caps, the others looked good. Has anyone had a need to replace these or is the general rule to just replace all of them?