Re: Tektronix 222 mini scope repair, looking for schematics


Hello Håkan and others,

After our return to warm Spain I finally got to taking my 222 apart, and obviously I directly downloaded the schematics as provided by Håkan (Many, many thanks for the scan!).

My scope has the following going on:

Somebody already replaced the battery-pack using NiMh cells. (2x7 AA-cells, 7 pairs of two cells in parallel, connected in series)
It does turn on and it does show a sharp readout, but no trace(s)
Both button panels are responsive.
When I do the Align thing it does show a sharp matching set of rectangular figures using the entire screen, as shown in the manual.
When I perform a Self Cal on both Ch1 and Ch2 it nineteen out of twenty times comes with a Pass as result.

But...... during the Self Cal I only see the right half of the set of lines going up-and-down.
So, although the readout is using the entire screen, the traces (and only during Self Cal) use only the right half of the screen.

When I set the sensitivity on both channels to 5mV and touch the probe-tip I do see some (apparently un-triggered) noise on the right half of the screen.

My thinking so far:

The Analog part (attenuator etc) is OK; (because of Self Cal do Pass)
The Horizontal and Vertical Amps are OK; (because of readout and align pattern are OK)
The Z amplifier is OK; (because of the two assumptions above)

I am thinking of half the storage memory being dead, or not clocked properly?
- Assuming the Self Cal is reading the AD converter's data directly into the CPU, so the storage/display memory is not used at that time?
- Assuming the Align thing is directly generated by the CPU, so the storage/display memory is not used?

Any thoughts or suggestions?
Anybody already repaired one of these little beauties?

To be continued, un saludo,


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