Tek 2215 problem

[jmgallag]

Hi,

Another beginner with scope repair questions... I picked up a 2215 in a stack of equipment pretty cheap. It was very dirty, and after some cleaning of the rotary switches with contact cleaner, I can get a trace. The problem at this point is the trace is only decent in the middle of the vertical adjustment, and the vertical seems limited. The first two pics are the top and bottom limits for ch 1. The third pic is the calibration square wave. The fourth pic is what the trace morphs into when moved up using the vertical position. At the extremes of the vertical adjustment, the trace becomes a flat line.

I have the service manual PDF. The power supply voltages are all within the stated ranges, except the high voltage. I don't have a HV probe, so I can't check that.

Questions:

• Could the HV supply be the problem? If so, I will get a HV probe to check it.
• Is this a likely bad CRT?
• Is the vertical circuit the likely problem? If so, I will continue to troubleshoot down that path.

Thanks,
Jim

[David Hess]

Could the HV supply be the problem? If so, I will get a HV probe to check it.

Probably not, when the x10 sweep magnification is *not* on, how many divisions wide is the sweep?  It should be about 10 to 11 divisions if the high voltage supply is working correctly.

Is this a likely bad CRT?

No, if the CRT was damaged, then the traces would be distorted on the screen relative to the CRT geometry and I see no evidence of that.

Is the vertical circuit the likely problem? If so, I will continue to troubleshoot down that path.

The vertical output amplifier depends on the +30 volt supply.  Make sure it is +30 volts and that the ripple is very low; an AC measurement using your voltmeter should read basically zero.

Check the condition of the collector load resistors at the output of the vertical CRT amplifier.  These are R378, R379, R388, and R389 under the neck of the CRT.  They run hot and may fail.  Inspect them to see if they are cracked or if their epoxy coating flakes off.

Does channel 2 operate in the same way as channel 1?

[jmgallag]

Thanks!

I will make those checks and post my results.

Jim