Last week I received this bad boy, a new addition to my collection of old glowing Tek instruments...
It's a type 180A, a " Time Mark Generator ". At least that's what it says on the face plate !
Vince, welcome to the 180A owners club! I think I picked up mine in the 80s, possibly early 90s.
My first 10 MHz clock source.
Thanks !
Progress has been made... it works now !!!
Well, needs fixing but it powers up just fine, no short anywhere, it was the DBT fooling me ! The bulb is only 75Watts so I though might not be enough.
So I checked the power supply thoroughly and didn't find anything wrong with it, so got rid of the DBT, applied power and voilà, the Tek powers up just fine !
I printed the schematic for the power supply so I know what I am doing. Check the primary and secondary windings of the transformer, no short.
Filter caps, not shorts. Cap values : still well within spec. The usual 10R series resistors on all the rails, checked OK as well.
There are no rectifier tube on this Tek. It's a late model / SN , 8000+ . The break point for all the mods is 5000, and one or two at 6000.
So mine has 100% solid state rectifiers, zero tubes. 3 full wave bridges. 12 diodes. Tested all of them, they were OK.
SO really, if really there was such a massive short like the DBT was suggesting, I would have found it !
That's why I took the risk to go without the DBT to see what I got.. thinking worse case the fuse will blow, that's what it's there for. Of course I did check that the fuse was the proper rating... it was. Looked like the original fuse to me.
So did that and as I said the instrument came to life just fine, no smoke no nothing... it just works !
At first the cooling fan would work. Pulled the air filter, saw that one blade was bent inward and interfering with the motor itself. Bent it back, now turns freely. Checked and adjusted the other 3 blades while I was at it, eye balling it. Fan now starts on the button and is quiet. A dream. The shaft does have an awful lot of axial play though, like a 1/4" or something... but apparently the motor doesn't mind....
So I fired up a scope to look if I could get something out of this Tek. First tried the sine wave output, on all 3 settings : 5MHz, 10MHz and 50MHz.
All work fine. I get a nice, clean, stable sine wave, with excellent amplitude, many volts peak to peak. Like 6 to 12Vpp depending on frequency. (the higher the frequency the lower the amplitude.
I measured it with my Ferisol Nixie counter, because it has an OCXO inside so it's my best counter for now.
Now I am basically measuring a 50+ year old OCXO with another 50+ year old OCXO, so it's hard to say which is which eh... but well, it's all I can do for now sorry !
The counter shows that the frequency is +100 Hz off at 5MHz, then +200Hz off at 10MHz, and +1,000 Hz at 50MHz. So it's all consistent.
Looked at the manual, states that the OCXO inside is good for 3ppm, so 30Hz off at 10MHz, when I get 200Hz.
So can probably be tweaked.... but not until I have a proper GPSDO reference so I can first adjust my counter !
For now all I can assume is that the error is spread across these two old OCXO, but have no way to know more than that...
Anyway, the time base, the heart of this Tek , is basically well and alive, good !
So then I tried to see if I could get markers to show up.... that were the trouble really start !
There are 14 settings from 1us up to 5s (in 1 / 5 steps) . 9 of them produce zero signal, nada, not a sausage to be seen on my scope...
Out of the 5 markers that do produce something, it's not all perfect either.
1us : not sharp at all.. will have to check the rise time in the manual. Might be normal, as this is the fastest setting.
2us : works, but one can see a slight "undulation" in the amplitude of the markers, they aren't all 100% the same height.
5us : same as above, but undulation is a bit more visible / pronounced. Maybe just tired caps somewhere, I guess, so not too worried at this early stage...
50us: they measure more like 40us not 50, and the amplitude looks like a "comb" : a short market, followed by a longer one, then a short, then a long... might again a ripple/tired cap problem... or something else entirely, not sure in this particular case...
100us : NO SIGNAL
500us : again more like 400us.. and signal was unstable, jumping to 300us then to 200+ or so, moving all over the place. After an hour testing all the 14 settings, I checked this one again and it looked like it improved : was stable now, and decided it wanted to be 400us. So 400us it is then
So maybe just dry and dodgy contacts... will squeeze a bottle of contact cleaner in there.... but I have ran out of the stuff, need to order some....
1ms : NO SIGNAL
5ms : NO SIGNAL
10ms : NO SIGNAL
50ms : NO SIGNAL
100ms : NO SIGNAL
500ms : NO SIGNAL
1s : NO SIGNAL
5s : NO SIGNAL
Obviously I have this read / white tube, which does not help, but I doubt it's responsible for that much defectivness, I just like to invent new words, it's not a Dragon monopoly I pretend.
Will replace it of course, see what that changes, but I suspect all the black/red Sprague crapacitors are dodgy, and might be used to couple stages together, which would explain a lot of my problems.
So will prepare a BOM and see how much that would cost me to recap...
Also of course need to measure voltage rails including ripple to check the health of the can caps.
Adjust the reference -150V rail if need be, or course.
So it's looking good I say, this things is alive, heart is beating, and it can produce "some" markers ! So the fundamentals are all there, I say !
Just needs some basic maintenance and it should be all good, me think... stay tuned !