Tektronix 7603 with 7B53A and 7A26 plug ins

[AlanBeckett]

Wonderful, well done.

I suspect your best bet for Spares is one of the Storage Versions. They're not popular and if one came up without any Plugins I doubt it would fetch much at all.

Alan

[Refugee]

Also storage tubes have a much shorter life than regular tubes so duff ones should be easier to find.

[Refugee]

I have been sorting out the dodgy 7A26.
It had a very intermittent loss of all gain on all ranges on channel 2 while channel 1 was all right.
You can see all the tool marks where the twiddler has been swapping the chips around to try and clear the fault.
I did many in circuit tests with a diode tester including the input junctions on the bipolar chips. They are transistor arrays. I eventually got to the wires and switches and found that the channel 2 invert switch was totally open circuit. It is a bit disappointing for Tektronix being just a little slider switch.
With twiddler evidence and the trace moving when some switches are operated indicates that the twiddler has been at the pots too.
Time to go through the calibration procedure now.

[AlanBeckett]

Splendid.That's cheered me up no end. I've bought some recently and about 50% seem OK but the rest have a variety of faults which could be a bit daunting. However, your experiences show they can be fixed.

Alan

[Refugee]

I did work in a test gear repair shop for a year or so and fixed quite a few 7000 series.
I used to work in the odds and sods department and took the scopes from the overspill from the scope department and got blasted with all the bounced jobs so lots of tough faults.
The other plug in is basically working and looks like just switch cleaning and a cal check.

[Radio Fixer]

I have been following along loosely but had nothing to add as I never worked on these scopes only used them.

But an impressive piece of fault finding and repair on what to me looks difficult to fix kit.

Well done.

Gary

[Refugee]

That FET in the timebase took quite a bit of testing to find.
It looks like the twiddler had some know how as not too much else has been touched.

[Refugee]

I have this evening been tackling the other 7A26 and it had also been twiddled and this time one of the DC balance pots had been moved so far off that the gain could not be set at all. The clue was that the manual warns you that they interact. The DC balance affects gain mostly.
On this plugin the twiddler had used a different tool to swap the chips around and all the legs are bent
I am now ready to finish off calibration and then it is sort out the graticule lamps and intermittent power switch and the electrics will be complete.
The only real fault was that FET in the timebase and the rest has just been twiddler related apart from dirty switches.
It was FOC with faults.
I am pretty sure it was "knocked up" from a load of faulty bits.
The search for something to replace the bottom panel and heat sink cover can now begin.
I have even made up a cable to compare two plug ins for calibrating one with another newly calibrated example. It will be a lot quicker than that a bench PSU and meter like I used on the first one.
As it is to be used as a main bench scope the cosmetically challenged side panels can stay as they are as the other equipment either side will hide it from view.

[AlanBeckett]

A splendid result

Alan