A Tale of Two Hypcons - Repair Report 7904A and Signal Standardizer


Tom Norman
 

There are a few posts here in TekScopes about the Tek Hypcon connectors, mostly around cleaning. It may be luck of the draw, but I've now had a total of 6 items that were not functioning properly, and were ultimately fixed with the disassembly and cleaning of a hypcon connected item.

A recent 067-0587-02 signal standardizer purchase had an issue with the bandwidth check leveling circuit fixed this way, as well as an apparently thermal issue with the vertical channel switch in a 7904A. The latter presented as a fairly rapidly decreasing gain on the right vertical plugin slot, which compressed the gain check display of the standardizer by about half over the course of the first 30 to 60 seconds of operation. The issue was with the scope, not the standardizer as the display was fine with the standardizer in the LH slot. After much use of IPA and ultimately freeze spray (to no benefit), I decided to just clean the dang hypcon, board and channel switch hybrid. This fixed the issue. The peak detect hybrid connector was at fault with the leveling on the standardizer.

So if you are experiencing apparently thermal related issues in an instrument that makes use of the hypcon connected hybrids, it might be reasonable to suspect the connector in addition to other discrete components or the hybrid itself. So far, I've been relieved to find that the elastomer used in the connector appears to not be degrading at this point ... at 35+ years of service.

While on the topic of hypcon connectors, I got some advice/help from John Addis while trying to fix an 11A34 amplifier. During that repair, he mentioned that some of the earlier hypcon frames had some issues with bending, that would unload some of the connections in the connector. This apparently was fixed by adding nylon to the recipe for the frame, and his email seems to indicate that some of these may have made it into the wild (not confirmed). So if you encounter a particularly troublesome connector, try swapping them out (if there are others in the unit). It's possible that the problem might be mechanical, and might be fixed accordingly.

Tom


Richard Steedman
 

Definitely agree that a careful disassembly, clean with IPA and reassembly does wonders. I've just completed a repair to a 7934 which was driving me a bit bonkers. Very strange trig behavior was eventually traced to the "Right off" input to the B Horizontal trigger channel switch being open circuit, so whatever was plugged in the Horizontal B bay (and anything looking at the rear Vertical Signal Out) was seeing a "Left+Right" (ADD) trigger signal regardless of the Vertical Mode selected. A good clean of the IC's hybrid and connector got things back to how they should be.