Tektronix 2215A

[AndrewBrolowski]

I just bought a Tektronix 2215A o-scope and it all functions work well EXCEPT that the both traces on the CRT gradually fade to becoming nearly invisible when the "A and B SEC/DIV" is decreased to below 0.2 microseconds (...and 0.1 and 0.05 being the last lowest time settings). I suspect it is degassing of the CRT but would really appreciate additional opinions before I tear into it.

Andrew

 

[davenn]

Hi Andrew
welcome to Electronics Point

tho you may get some answers here
if not there a really good tektronix group on yahoo groups
that I have belonged to for many years and lots of very good help will be found

http://groups.yahoo.com/group/TekScopes/

cheers
Dave

 

[elebish]

I just bought a Tektronix 2215A o-scope and it all functions work well EXCEPT that the both traces on the CRT gradually fade to becoming nearly invisible when the "A and B SEC/DIV" is decreased to below 0.2 microseconds (...and 0.1 and 0.05 being the last lowest time settings). I suspect it is degassing of the CRT but would really appreciate additional opinions before I tear into it.

Andrew

Most scopes use a brightness enhancement circuit to brighten the trace when the time base switches to higher speeds. Sounds as though your problem is the opposite! I would check the crt cathode voltage at different sweep speeds. The potential should be approx. a negative 2400 vdc. There are also "unblanking" circuits that are used for eliminating the retrace lines that are controlled by sawtooth waveforms that are produced in the horiz sweep circuits. The trigger circuits provide the trigger to start the sweep. Make voltage measurements in the Z axis and horiz sweep circuits first but be careful of the higher voltages that can bite.
Another problem can be the persistence of the phosphor is degraded enough to not maintain a bright enough trace when sweep speeds are slow. That would indicate a bad crt. NOTE: The high voltage to the anode of the crt should be about 12000 to 15000 vdc, enough to cause severe dilatation of the eyeballs! Ed.

 

[OLIVE2222]

The service manual is available here:
http://thehistoryofrecording.com/Te...ktronix_2215A_Oscilloscope_Service_Manual.pdf

I second Dave regarding the TekScopes Yahoo group, very nice people there (including former servicing engineers)

Good idea by the way to maintain old but valuable equipments in service !

 

[shrtrnd]

All good advice above.
The first thing I'd do however, is increase the CRT 'intensity' pot, to see if those signals become visible.