EEVblog #620 - Repair: Stanford Research SR650 Programmable Filter

[Tothwolf]

I just got another old not working gear from ebay. Those GPIB nuts are always corroded (like in this case), what is the best way to clean them up/stop the corrosion?

I've seen this lots of times too. I guess they either made the jackscrews out of unplated steel or just did a black oxide treatment.

Assuming you can find them, the easiest fix would be to replace those jackscrews outright with some that have some sort of plating (zinc, zinc with yellow chromate, nickle, etc). If you have to clean them, electrolysis cleaning is going to be your best bet. Because the parts are so small, it would be extremely easy to clean them electrolytically in a small container.

As for preventing rust, you could either electroplate them (zinc, copper, nickle, etc), powder coat, or just paint them. Since most people aren't set up to electroplate or powder coat, I'd suggest spraying them with clear lacquer (not acrylic enamel). A clear lacquer will hold up much better than an acrylic enamel paint. A black lacquer paint would work too, but I've found clear to be more resistant to chipping in these applications.

[Tothwolf]

Mark, Ian,

Any chance either of you could verify which thread and length of screws are used for the power transformer/fan/heatsink/regulator and top cover? If I knew exactly what they used, I could see if I have some I can send Dave from my stash of fasteners.

[IanJ]

Mark, Ian,

Any chance either of you could verify which thread and length of screws are used for the power transformer/fan/heatsink/regulator and top cover? If I knew exactly what they used, I could see if I have some I can send Dave from my stash of fasteners.

There's a parts list which includes the hardware at the back of this manual.

http://www.thinksrs.com/downloads/PDFs/Manuals/SR640m.pdf

Ian.

[Tothwolf]

Mark, Ian,

Any chance either of you could verify which thread and length of screws are used for the power transformer/fan/heatsink/regulator and top cover? If I knew exactly what they used, I could see if I have some I can send Dave from my stash of fasteners.

There's a parts list which includes the hardware at the back of this manual.

http://www.thinksrs.com/downloads/PDFs/Manuals/SR640m.pdf

Ian.

Odd, it doesn't look like it is complete. The longest screw I see listed is a 6-32 x 1-3/8" and that doesn't look like it is long enough to fit through the power transformer or fan and into the heatsink. From Dave's video, it looked like they used 8-32 screws there, too. There isn't a breakdown diagram with designations in the manual either, so I have no idea which length 4-40 they used for the two TO-220 devices or how long the original chassis cover screws are. I'm also still not sure if they used threaded inserts for the two TO-220 devices. I don't know what all I'll have in my hardware stash that will work, but I'm overdue to reorder other fasteners, so whatever I don't have already on hand I can tack onto my next hardware order.

[IanJ]

Mark, Ian,

Any chance either of you could verify which thread and length of screws are used for the power transformer/fan/heatsink/regulator and top cover? If I knew exactly what they used, I could see if I have some I can send Dave from my stash of fasteners.

There's a parts list which includes the hardware at the back of this manual.

http://www.thinksrs.com/downloads/PDFs/Manuals/SR640m.pdf

Ian.

Odd, it doesn't look like it is complete. The longest screw I see listed is a 6-32 x 1-3/8" and that doesn't look like it is long enough to fit through the power transformer or fan and into the heatsink. From Dave's video, it looked like they used 8-32 screws there, too. There isn't a breakdown diagram with designations in the manual either, so I have no idea which length 4-40 they used for the two TO-220 devices or how long the original chassis cover screws are. I'm also still not sure if they used threaded inserts for the two TO-220 devices. I don't know what all I'll have in my hardware stash that will work, but I'm overdue to reorder other fasteners, so whatever I don't have already on hand I can tack onto my next hardware order.

I'm metric and not hot on US sizes etc. But hope these pics help.

Ian.

[Tothwolf]

I'm metric and not hot on US sizes etc. But hope these pics help.

Ian.

The photos help some but I still can't tell for sure what they used. I'll have to try measuring them in a photo editor using the rule in the photo as a reference. I'm still not sure if they are using 8-32 or 6-32 screws for the transformer/fan/heatsink though. The transformer/fan/heatsink screws do look to be about 35mm long, or ~1-3/8in, which means those very well may be 6-32 x 1-3/8" instead of 8-32.

Are the kepnuts on the 4 small standalone heatsinks smaller than the nuts used for the fan and transformer or are they the same size? Those 4 heatsink screws can't be larger than 6-32 due to the size of the hole in the TO-220 device's tab when used without an insulating shoulder washer (when using an insulating washer, the largest screw you can use is a 4-40).

Metric fasteners tend to give me more trouble than english sizes. There are more combinations of sizes and thread pitches with metric fasteners compared to the common sizes of english fasteners.