Jim Garland <4cx250b@...>
I'm helpinga a friend troubleshoot a Tek 2215 which has a vertical input problem. The symptom on Ch1 is that the DC balance isn't right. The position of the trace shifts (with grounded input) as one changes the vertical sensitivity. On some sensitivity settings, the trace moves off screen (although it can be seen with the beam finder. On Ch2, the sympom is similar, but worse. The trace is always off screen, and the position control can't bring it on screen.
I've not worked on the 2215 before, and am surprised there's no front panel DC balance adjustment. I thought that was pretty standard on Tek scopes. Any suggestions about what to adjust or where to look for problems? BTW, this scope was a $50 hamfest "special," so it's not surprising it has a few issues!
Sometimes a DC balance problem is an indicator of a power supply problem. Have you checked the power supply voltages and ripple?
Also, I think some of the chips are in sockets in the vertical input section and you might try reseating them.
Do you have the service manual?
The only balance adjustments are internal and for the 10 to 20
millivolt step attenuator balance on each channel.
Check the power supply voltages. You might also want to check the
power supply voltages at U145 and U245 to verify that both channels of
the +8.6 and -8.6 local supply voltages are not missing. There are
some low value resistors shown in the bottom left corner of schematic
1 that supply the power supply voltages to the front end circuits.
Check the voltages there and check the resistors to see that none of
them are open.
Inspect the area around schematic 1 for contamination on the board.
Maybe the oscilloscope was left out in the rain? After a few minutes
of warm up, do the baseline traces drift around a lot? Do they drift
if you blow on the printed circuit boards around the inputs with your
Does changing the input coupling switch cause any movement in the
trace position when the input is grounded?
On Wed, 5 Dec 2012 08:29:41 -0700, "Jim Garland" <4cx250b@...>
I'm helpinga a friend troubleshoot a Tek 2215 which has a