Tektronix 544 Oscilloscope
The 544 scope
Specs: 50MHZ bandpass, Weight: about 28KG, Serial number: 488
Got this one of a man in roosendaal, he was moving and wanted to get
rid of some stuff. But he wanted to give his old scope a good home.
Well i got it with a probe, lighting shield and an nice cart to put it
on. Its quite an old machine but compared to the other scopes i got, it
has lots of sillicon inside. Tunnel diode with transistors triggering
circuit amplifiers are all transistorised, but the powersupply is tube
only.
When i got it i could notice by the amount of dust that it stood for
quite a while, but it worked first time i turned it on.
After closer inspection it seems that it had some problems.
- The second channel was really weird, it didnt work at all.
- Screen getting dimmer over time..
- No triggering at all.
The first problem was fixed quite quickly, with the aid of contact
spray and a Q-tip i gotten rid of all the intermittent switches, except
the calibrator still is a bit shaky. But acceptable.
The second problem was very concerning, i read that all the 54X series
had the same flyback transformer and that its insulation would age and
get lossy over time. After a while the insulation heats up becouse of
leaking electrical energy, heating up the insulation more. Until the
oscillator providing power to the tube cuts out. Well it seems to have
this problem as after a while it really gets dimmer.
Well one day i was working, and heard a strange arcing sound, the scope
does not respond well to brighness settings now. I need to look into
that problem when i have the time. But it does not go dimmer over time,
i will check the voltages soon. If nothing is not too high i will
probably keeping it like that. Maybe check for obvious failed parts.
544 Triggering and timebase assembly, ceramic strip construction
was used a lot in this scope.
The third problem was the triggering, well i was first under
the
impression it was the tunnel diodes. How wrong i was, i should first
check everything out and measure with an VOM or a scope if everything
is okay. Well i have actually never fixed anything made out of discrete
electronic components. Well after measuring the voltage of the
tunneldiode kathode, it seemed way off. Much too high, i then checked
the main powersupplies, and they where way off too. All by 16% or soo,
moving the 150V calibration potentiometer did lower the voltage a bit,
but not by much. Something failed in the powersupply.
Powersupply, the tube next to the big metal potmeter had failed.
Well i looked and asked around, and somebody of the tektonix
group at
yahoo told me that the most common failure he saw in these scopes of
these series was the neon voltage reference tube, so i went to measure
there. Bingo! it should have been 87 volts but it measured 99! about
16% difference that the other voltages where off! Ordered a new tube at
this site,
put it in and adjusted the voltages. Triggering seems back to normal
but only a bit picky, maybe check some settings like center balance and
sensitivity. But it works fine for the rest.
The 544 showing 2 traces of the calibrator output.
Well this scope has an higher bandpass then the 545B, but doenst have
the dual timebase (not that i use it that much). Now its completely
fixed i use it as my main working scope.
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Last update at: 03-06-2005