Hi!
1) Service Manual; Service Manual, Service Manual!
2) Power Supply Rails, Power Supply Rails, Power Supply Rails!
I've repeated these two items three times in light–hearted vein to emphasise how inportant they are in dealing with any defective piece of Tektronix equipment!
The 2213 Service Manual can be downloaded free from many places, such as k04BB, TekWiki. BAMA, Kevin Chant, etc., or a high quality copy can be bought from Artek for about £10 (12–15 USD)
ALL Tektronix equipment is critically dependent for stable opertion on all their internal power supply voltages – the values and the amount of allowable noise/ripple on each of the various power–supply lines is given on the diagrams and on the circuit descriptions.
Please get yourself a good copy of the 2213 S.M. and study it carefully, then begin with voltage and ripple tests on the power supplies, if anything doesn't measure right please get back to us with your readings!
Chris Williams