Exact Model 126 Function/Sweep Generator - Page 1
Forum section: electronics / repair

author: Cyberdragon
author_rank: Super Contributor
timestamp: May 17, 2017, 06:52:04 pm
content: If anyone has the manual or shematics it would be appreciated.I've already had to replace some of the trimmers that were bad with ones dangling from wires, but all the ones I replaced seem to carry DC only so it should be okay, as long as they don't get near other components. (right?)The problem is the ouput is unstable and won't adjust. When I try to adjust the 1000:1 pot (which is one I've changed twice now) to what it says on the cover, the wave is a triangle as it should be, but the frequncy jumps all over the place when I turn it. It sort of goes up and down, but in huge unstable jumps and jitters around a certain frequency where you leave it. The sweep cicuit is turned off. Does it hate my bodge or is there something else wrong? I have confirmed DC only on the leads to the bodge trimmer, so there shouldn't be an impedance problem.I have noticed a tiny ripple on the power supply, and an ugly looking signal on some resistors around the circuits that are producing the triangle wave. But without a schematic I have no idea where this signal is coming from. It's also really hard to make measurements not referenced to ground since the unit itself is referenced to earth ground, so any attempt to measure a signal across two points would short the unit through the scope lead. I could disconnect the ground, but I don't know what that would cause.

author: tautech
author_rank: Super Contributor
timestamp: May 17, 2017, 08:29:49 pm
content: Here's model 240 from KO4BB that might get you started in the right direction:http://www.ko4bb.com/getsimple/index.php?id=download&file=06_Misc_Test_Equipment/Exact_Electronics_240_Function_Generator_Operator_Manual.pdf20MNot checked, it's listed as OM so not sure if it has schematics.

author: Cyberdragon
author_rank: Super Contributor
timestamp: May 17, 2017, 09:19:51 pm
content: Unfortunately that is an entirely different machine, at least a decade older than mine with no ICs.

author: Cyberdragon
author_rank: Super Contributor
timestamp: May 17, 2017, 09:37:49 pm
content: Another one bites the dust. Another trimmer failed, I'll see what replacing it does.EDIT: It's the positive triangle peak trimmer

author: tautech
author_rank: Super Contributor
timestamp: May 17, 2017, 09:49:17 pm
content: Try this one then:http://www.aef.se/Instrumentmuseum/Instrumentportal_ny/Dokument/Enstaka/128_Instruktion_Manual_3854.pdf

author: lowimpedance
author_rank: Super Contributor
timestamp: May 18, 2017, 02:46:02 am
content: Many many moons ago I had a 126 with the manual , but gave it away long ago with the manual. How ever I did copy "bits" of the manual when I was servicing it thus not the complete manual.Attached is what I have got on the 126.Note the 128 linked above looks very similar cct wise when you remove the extra functions between the two. So with both sets of info you should be able to nut it out.

author: Cyberdragon
author_rank: Super Contributor
timestamp: May 18, 2017, 02:51:23 am
content: That should be close enough, the VCF input is a bit different but hopefully everything else is nearly identical.