IEC (Interstate Electronics Corp) F51 function generator - Page 1
Forum section: electronics / repair

author: Zenith
author_rank: Frequent Contributor
timestamp: July 10, 2022, 12:02:31 pm
content: Some time back I was given an Interstate F51 function generator. Judging from dates on some components it was made in 1970. Internally the standard of construction is very high, and it must have been expensive when new. The plastic panels at the front, and particularly the back, have suffered with age.When switched on, after about 20 minutes, it comes to life. It has a PSU supplying +/-24V, +/-12V and +/-5V, all brought out on nice labelled test points. Checking the test points shows around zero volts until it eventually starts to pick up.I don't have a manual for it, and can't find one on the web, even for money. I have found manuals for F30 series and F40 series. They have PSUs which supply about +/- 30V unregulated for the O/P amp, and +/-15V and +/-5V regulated, with everything referenced to the +15V line. I assume there's a close resemblance between Interstate PSUs of the time and the F3X and F4X supplies are near identical. This is somewhat different in that there are two bridges of 1N4007 rectifiers, not one. The other odd thing is that there are four 709 op amps in 14 pin DIL packages, rather than two in the F3X and F4X supplies. One of them is socketed and that looks like a repair, with the socket added by the repairer. It looks as if the 1N4007 rectifiers have been replaced as well.My guess is that everything is referenced from the +24V supply and this problem is caused by a faulty zener or op amp.Can anyone help with a schematic for the PSU, as proceeding without one is hard work? A complete manual would be better, so that the FG could be set up properly. Recollections of working on the IEC F51 would also be good.

author: Jeff eelcr
author_rank: Frequent Contributor
timestamp: July 11, 2022, 01:25:24 am
content: I have rebuilt F40's and F77's 30's are similar even 20's but never any 50 seriesThe supply looks very differently layed out?At this age filter caps they used failed also tant caps usually 6.8uf but where arethey in that supply?Jeff

author: Zenith
author_rank: Frequent Contributor
timestamp: July 11, 2022, 09:53:32 am
content: I can't see a tant anywhere in it. On the top board there are a couple of tunnel diodes, transistor arrays and several Texas dual transistors with numbers I can't find - maybe specially selected for IEC . I'd guess it was designed in the late 60s just before tants hit the scene.IEC equipment isn't that common these days and the F51 seems particularly uncommon.As I said, I assume the rest of the supply rails depend on the +24V rail and that has a failing component. It should be possible to fix it with some deductive work, but it would be far easier if some kind soul produced a schematic for at least the PSU.The problem is it's too good to throw away, but it's not good enough to keep, and it's almost working.

author: Jeff eelcr
author_rank: Frequent Contributor
timestamp: July 11, 2022, 12:28:28 pm
content: Even the electrolitic caps are different type, not usually axial on PCB.Have you checked with Artek manuals ask him sometimes he has accessto ones not listed.I am still looking for a P23/P25 IEC manual.Their equipment was upper lower end or middle good quality, stable, repairshops bought a lot and some labs. Usually all metal case no plastic.They have been gone a long time now to bad it was a good company.Jeff

author: Zenith
author_rank: Frequent Contributor
timestamp: July 11, 2022, 06:41:43 pm
content: Thanks for the suggestion. I've emailed him and I'll see what turns up.The F51 is something I've had for years. Sometimes I dust it off and have another look at it and see if a manual has turned up on the WWW since the last time. I suppose I could fix it without a schematic of the PSU but it seems a lot of work. Maybe a project for a winter's weekend when everything else I have to fix has been fixed.