Tektronix 5L4N Spectrum Analyser

ID: 219240
? Tektronix 5L4N Spectrum Analyser 
26.Apr.10 15:34
54

Mark Andrews (GB)
Articles: 88
Count of Thanks: 13
Mark Andrews

Recently got hold of an old Tektronix mainframe scope with a plug in LF Spectrum Analyser module. After chasing my tail with a dry joint on the PSU, I now have it working pretty well though it has one fault which I would love to solve!!

When switching to LOG mode, it should scan from 20Hz to 25KHz instead of the 100Hz to 100KHz. This mode is intended for audio amps etc and is the reason I got it. Well the mode does work after it has been sitting running for 10mins etc however when cold it only drops to 80Hz. the 25KHz still selects OK. Prblem is when I hook up an amp to test, the bottom end trace is wrong.

Anybody out there got experience of this and any ideas about fixing it? I have downloaded the schematics and had the thing to bits but so far I am stumped!

Mark

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 2
Please create new model 
27.Apr.10 11:40
54 from 7195

Bernhard Nagel (D)
Officer
Articles: 1681
Count of Thanks: 11
Bernhard Nagel

Dear Mark,

since the Tektronix 5L4N spectrum analyzer isn't listed here in RMorg, it would be a valuable addition to the family of already existing TEK service instruments. Please add also the mainframe as a seperate model (is it from the 5000 series?) if necessary. Your inquiry should be moved to the new model when online.

Bernhard

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 3
New models 
27.Apr.10 11:49
61 from 7195

Mark Andrews (GB)
Articles: 88
Count of Thanks: 7
Mark Andrews

Hi Bernhard,

I will create three new models for each part later on today.

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 4
Faulty Tantalum ?? 
27.Apr.10 13:59
79 from 7195

Mark Andrews (GB)
Articles: 88
Count of Thanks: 9
Mark Andrews

Some more information!!

Traced the fault I think to a -15V regulator board which uses an LM301 plus power transistor. If I freeze a tant cap when this is warmed up, the low end plot goes to pieces but then restores itself! A tantalum cap should not be affected by temp and a regulator circuit should cope with temp changes??? What do you think?

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