Re: 454 screen brightness issues?


Jack Ohme
 

Mike,

I have a copy of the manual in PDF and on paper. The intensity dial
correctly changes the voltage (although the screen brightness shows no
change), but the grid biasing potentiometer does not change the voltage at
TP1349, which stays at around 6.8v. I'm not sure whats happening here, if
this is the grid biasing pot that is broken or something nearby on the Z
axis board, but I will inspect the schematics. Let me know if you think of
anything to look for.

-Jack

On Mon, Jan 6, 2020 at 2:15 PM Albert Otten <aodiversen@...> wrote:

Hi Jack,

Where should I be looking for those DC restorers, in the -1920v?
The 454 has no DC restorers. The HV transformer has separate windings for
the grid and the cathode circuit. The rectified voltage for the grid can be
reduced somewhat by the grid bias pot R1447 (in the divider chain with
R1442-R1446) and is stacked on the voltage supplied by the Z-axis
amplifier.
When you follow Mike's suggestion and use a pdf of the manual, you will
note that the waveform at TP1349 is almost invisible. The blue picture in
the paper manual is also very faint. The voltage switches between the 2
written values 17.7 V and 6.75 V.

Albert



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