4. Tek 7S14 100ps Dual sampler plugin
(a) Horizontal sweep only scans at about 1cm/s at its fastest.
Initial investigation suggests the tunnel diode oscillator is faulty, probably due to either or both of the TDs out of spec or dead. I want to test them on the Tek 571 curve tracer but I could find no information on how to do this. I don't want to risk destroying them as they are hard to find and expensive at $30 ea just on eBay.
The 7S14 delayed ramp gen has the following tunnel diodes:
Service Manual circuit page P.5A CR459 Tek 152-0169-00 1.0mA 10pF aka GE 1N3712
Service Manual circuit page P.2 CR220 Tek 152-0177-00 10 mA 4pF a Tek special
Service Manual circuit page P.2 CR221 Tek 152-0070-00 0.1mA 3pF aka GE 4JFBD4 (GP tunnel diode) American Microsemiconductor also made it
However there are a plethora of Russian tunnel diodes on eBay (see my tab 'USSR Tunnel Diodes Xref' for specs). I compared as many as I could find and selected three as close as possible to the Tek parts and ordered several to experiment with on the 571. Once I know how to test these safely, I'll check the Tek ones too, and if they are faulty I'll see if I can replace them with the Russian ones.
(b) Both input channels inoperative
Initally both traces were wiggling up and down randomly at slow speed when plugged into a Tek 7834 and its cal fed into the 7S14 inputs, but they were not showing any evidence of the calibration
waveform. A well known fault with the 7S14 is the 4 Hg batteries hidden in the shielded compartments of its input section have run out - see here:
Sure enough this was the case - this 7S14 was sold as 'tested' but these batteries were so badly corroded I'd guess it hasn't been used for 20 years. The original battery was a Mallory Duracell WH3 1.35V 220mAh Hg cell 11.56mm dia x 5.4mm thick. I followed the excellent advice and replaced them with AG10 = LR54 1.5V 60mAh alkalines 11.6mm x 3.1mm dia only because the only coin cell holders I could find would not take the thicker AG13 (LR44) 200mAh. This produced two steady traces but still no calibration waveform visible. At least the level controls work.
(c) CRT readout is momentary
Another strange fault is the readouts (V/div, T/Div) only appear momentarily at the start of a sweep.
Apart from the above, it would seem it works - even the delayed bright spot used to measure waveforms functions, although of course I have no idea of its accuracy.
To be realistically able to repair the 7S14 requires two of Tek's 067-0616-00 7k series plugin flexible extension leads but as with anything so useful, a high price is commanded on eBay and they usually go for at least $150 each. I found a low cost alternative solution available here:
http://ecosensory.com/tek/tek_7K_flex_sales_blurb.txt