Oscilloscope B&K Precision 1472C Intensity problem !

[guizmo1967]

Well, maybe !!

Since I don't have a second scope, I have to take the long road ....

I removed the sweep time and the vertical amp board once again to test every resistors and diodes with my DMM, something I did not do before. No open resistor found, maybe some's were out of spec but once removed they were good. No bad diode either.

I decide to look at the production changes for the 1472C and to my surprise not all the modifications has been done 

Mod 1:  was already done

Mod 2a: was already done

Mod 2b: was already done

Mod 2c: C139, C140, R222 and R223 by following the trace, not even there !!

Mod 3a: was already done

Mod 3b: was already done

Mod 3c: was already done

Mod 3d: It was indeed a 6.8K with no C248 ?? Replaced with a 4.7K and added C248

Mod 3e: C249 and L209 not even there !!  I have to buy those parts.

Mod 3f: was already done

Mod 3g: D213 was missing ?? I added a 1N4148 from IC204 pin4 to pin12.


I put everything back together even if mod 2c and 3e are not done yet. Turned on the scope and now I have a pulse (max I saw was 318KHz) at P202 pin2 that varies when I rotate SWEEP TIME/CM, that's a small progress !!! When I adjust VR2, the voltage at P309 pin2 goes form +2.7V to +5.04V.

When I play with MODE (CHA, CHB, A&B, A+B, A-B) and VR2, I can see the intensity changes depending where MODE is.

I still don't have a pulse at pin 12 of IC202

That's all I can say for now