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Tek R5030 refurb done, lots of interesting issues...fixing the fiber-optic readout


 

The R5030 is a very unusual scope, ti has the large CRT and fiber-optic display like the 576 curve tracer, and
the lighted function switches from the 7K plug in series, along with amazing sensitivity down to 10uV/division. yes, microvolts. Kind of a 7A22 merged with a 576 and a 5K rackmount.

I got three repair candidates from Dennis (to fulfill a long time desire), and was able to get one fully working, the others have too many fatal flaws to be anything other than organ donors. I found many strange problems, and was amazed to discover that on all 3 units, the blue covers had been installed incorrectly, (differently!) blocking the scope's required ventilation. In the one I repaired, the output stage got so hot, the power resistors actually de-soldered from the pcb.

Once re-organized, the covers work correctly, and the scope runs OK, although I have to say, like all 5K systems, it just gets TOO hot. The tricky part was getting the fiber-optic display up and running again. In my case, every display was bad, with so many pixels gone, nothing was readable.

The manual pretty much ignores the display in every way, there's no info on it at all other than a mention of the lamp types in the parts list (150-0048-01 / 683 5V T1, flying lead types). The big question was, how the heck do I get to the display to fix it? It is buried behind the panel, with no obvious way to remove it.

Thanks to some list members who have worked on the 576, the answer was to remove the CRT bezel and all the overlays (there are three, remember the order!) to get at the front of the display itself. The display then pulls forward (no hardware), and can be extracted if all the mating harmonica cables at the rear are removed. WATCH OUT, some are smaller than the headers they plug into, be sure you know how to align them when replacing the cables! All should start at the right side (viewed from the front), there will be a few exposed pins to the left on same middle cables.

Once out, the display module has three covered assemblies, remove the aluminum covers (two screws) to get at the lamps and fibers below. I REALLY wish they had used a based T1 lamp, but every lamp has to be hand soldered in place in a tiny board covered with interconnect wires. not the best bit of production design at Tek, that's for sure. The black assemblies pull to the rear to expose the lamps.

Be careful of the brittle fiber optic light pipes, they run through the lamp assemblies and could be easily damaged if you get impatient. gently pull the black light assembly free of the metal mousing, and expose the rear board. you will have to cut some cable lacing to do this, it is too tight otherwise. My technique was to use a pair of surface mount test tweezers hooked to a bench power supply (set to 4.9V, and c/l of 0.12A) to probe each set of lamp contacts, there was no other easy way to make both connections at once. Once side of the lamps is common on the boards, the other goes to a wire that heads back to the connectors. Polarity is not important in probing the lamps.

As you hit each lamp, you should see it light (even from the rear), I found one lamp installed that was the wrong type, it drew way too much current, and was dim (good lamps will draw about 50-60mA)., I also removed any marginal lamps. it took me about a dozen lamps to restore my assembly. You have to carefully de-solder each lamp (don't burn the wires), clean the holes, then tread in a new lamp, being careful not to twist the leads so they short. Once fully in and centered, re-solder the lamp. Test each lamp when done, you don't want to have to go back in this thing again.

Once all the lamps in any section are all good gently re-seat the black base into the metal housing, be careful not to damage any fibers or pinch any wires. Once a full display is good, re-install the metal cover (2 screws), being careful not to trap any wires between the cover and the chassis (this can happen very easily). Once all three displays are done, the entire display board can be re-slid into the fitted slot next to the CRT. The last step is to re-connect all the harmonica connectors in sequence, being careful to align them properly (un-connected pins will be to the left).

Adjusting the display dimmer (below the two intensity controls) will adjust both the CRT graticule light and the displays. with luck, all the digits and symbols will now illuminate correctly!

If anybody wants to see the pics of my completed unit let me know I can email them to you. I was able to transfer the Option 04 desktop carry kit to my unit, and remove the rack parts to make mine into a proper bench scope. The final result is very nice looking, and operation down to 50uV/Div works very well, below that noise can be a real issue. Operation at 10uV would have to be into a very low impedance via a short shielded cable. They were maybe optimistic on that range.

All the best,
walter (walter2 -at- sphere.bc.ca)
sphere research corp.