Re: Tektronix 222 Repair

John Gord


Pin 14 on the TL594 is VREF, listed on the data sheet as 5v. The two pins are tied together, so those pins are probably OK.

<<>> might have more accurate schematics for the 222.

--John Gord

On Sun, Apr 12, 2020 at 12:23 PM, <> wrote:

Hi All!
I have a Tektronix 222 scope that doesn't work. It won't startup.
Battery is dead so I'm powering it with the external jack with a bench supply
set to 14V.
When I apply power the Trigger led blink for a second and I can hear a "beep",
after that nothing happens. Doing some test on the Power Supply Board (A4)
I've found that the power FETs that drives the main transformer becomes very
hot (the unit in this state draws about 12W of power so there's something
After some tests I've isolated the 120V line after the transformer, now the
scope draws less power and the FETs stays cool but I can't make it work.
I'm using the 222A service manual which include boards schematics, they are
not exactly the same but pretty similar:
In the troubleshooting procedure guide I've read that the pin 13 and 14 on the
TL594 on the Power supply board should stay near 0V in normal operation, on
mine they always stays at about +5V.
I think taht something isn't working properly on the power supply board but I
can't find what.
Do you have any idea? Any help will be appreciated!
Thank all!

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