Oh wow it's 4H30 almost, eyes are getting tired... need to go to sleep, but I will post this quikc before I go to sleep !
Look what I foudn in a some random box ! I had completely forgotten about this thing ! An old retired engineer friend gave me a ton of stuff 3 years ago, including some TE, but never had the opportunity so far to check out everything he gave me... so here is what I just found !
A HP 3200B VHF oscillator !!!
Can do 500MHz !
I can do " RF " now !
At least I can check the B/W of my scopes and probes and frequency counters, and play with filters ! Can do a bunch of stuff with this thing !
Seems to work just fine all the way to 500MHz. Only thing I see wrong is the amplitude knob. Well the one at the bottom right, that doubles as a power switch... I guess it's the amplitude knob.
However it does not do much ! If I crank it all the way, I get only about 20/25% increase in amplitude compared to its minimum setting !
Will have to investigate that.... service manual is available I guess.... since he gave me printed copy of it... so there is hope.... or not : I cracked it open. all the RF black magic happens behind closed doors, inside a beautiful, huge super heavy die cast alloy enclosure ! No human allowed inside for sure... so I don't know.
500MHz so... for once, out with the 200MHz combiscope, and in with the TDS 544A (500MHz B/W). A good opportunity to give it some use eh ?
So it looked all kinda nice until about at 400MHz where the sine wave become very unstable, amplitude goes all over the shop, scope can't trigger on it anymore.. even though it should, regardless of the amplitude going hay wire, because signal is clean, plenty of signal amplitude to trigger (on zero crossings here).
Looks weird so I made a short video clip of it to show you, below.
I found it strange that the HP generator could exhibit this kind of behaviour, so to double check, I fired my TDS 694C, 3GHz 10GS/s, should do it eh....
As soon as I powered it up... ran into a problem : once it's booted, you need to press the " Clear Menu" button in the bottom right corner of the CRT keypad, to make the POST message go away. Pressed that button.... no go, not a sausage ?!
After a few seconds, message goes axway by itself lucliky, buty still. Then I enter some menus and ... yeah sure enough I can't exit the menus, button never works. All other buttons around the CRT work fine, just not the CLEAR MENU one.... so need to check the menbrane keypad in there. However I bet it's designed the same way as my TDS 310A, which the same problem (with the "Standy by / OFF" switch though), and it ended up in me butchering the keypad beyond repair, had to rip it off the chassis and now scope is not economically repairable... you just don't find these keypads, never mind at low enough price that it would make sense for a bottom of the barrel 310A.
Anyway... even with the trigger chips dead, I could still see the signal by single shotting it using the "Force Trigger" button on the front panel.
I did that a few times in a row and noticed that the amplitude of the signal was always the same.... which does not add up. That would tend to mean the signal is just fine, not unstable, and it's just the TDS 544A that fails to trigger properly past 400MHz or so. So... now I have to fix that as well ! I hope it's not a hopeless case of " need that obsolete unobtainium Russian tunnel diode that has zero cross-ref / substitute... ), ... but I fear it's gonna be just that...
So I had my two fancy TDS scopes that could eithe rnot be trusted, or severely impaired.
What do you do then ?? Of course only one solution ! You fire up your analog scope !
So I pulled my 2467B that I got a year ago (but never mentionned here I think...), which I actually never used. Tonight is the night babe !!!!
I have not even cleaned the gross front panel, yikes !
Powers up fine... but readout and trace are blurry, can't focus properly, never sharp. Also they are "noisy", so to speak. So me think the electrolytic caps in the PSU need replacing. Other than that, it's a champ : can display the generator at 500MHz just fine, even though it's a 400MHz scope. Sure I lose some amplitude, but I still have enough to get a trace full screen, and for the scope to trigger on it perfectly... and boy that MCP tube... at 500MHz, with the time base at full blast + x10 mag... the trace is so bright you have to turn it way DOWN not to get blinded and burn the CRT !
It needs to be see to be believed... these scopes are absolutely phenomenal... until you have seen one do what it just did tonight, you would not think it's possible... these MCP tubes are just out of this world. I am so glad I bought one ! I understand they can get weak/dim fast... but mine is clearly very healthy !
Anyway, thank Tektronix for this marvelous scope... it showed that the generator even at 500MHz works just fine. The amplitude is perfectly good, and stable.
So it's indeed my TDS 544A that's losing it above 400MHz... CRAP !!!
How a I going to fix that now, oh dear me....
30 seconds later.... I hear a fire works inside the 2467B, and 2 seconds later, a big cloud of white smoke comes out the rear of the scope and starts filling the living room !!!
So looks like it's not just the electrolytics in the PSU that needs replacing... the bloody RIFA just gave up the ghost as well !
But that's fine... this scope has proved how exceptional, breathtaking it was technically, so I am mooooore than happy to take it apart and do all the servicing that needs doing to get it back into shape...
So to suim it up.
- I just got a cool HP 3200B 500MHz oscillator that's got a defective attenuator.
- A TDS 544A scope that can't trigger (or other problem ?) above 400MHz... reducing the usefulness of the scope somewhat...
- A TDS 694C that needs a keypad fixing...
- A 2467B that escaped the magic smoke.
4 TE to fix in just one hour, what a performance !!!
I think I deserve a good
night/morning of sleep now... to recover a bit...
Good night....
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Topic: Test Equipment Anonymous (TEA) group therapy thread (Read 14823145 times)