Tektronix 434 repair , dead scope

[Jorge4563]

Hello guys, I came across this amazing electronics forum and decided to give a shoot to a broken scope to test my skills. I know the 434 is not an amazing scope but it was only 39 dollars and is in excellent cosmetic condition. This scope is the option 1 and is dead. The power supply sounds like clicking, even without load (no boards connected). I have checked the main power transistors and main capacitors. Can i please have some pointers to continue my mission ? I really appreciate any help. I have a multimeter and and LCR meter, as well as some spare caps and resistors.

[bd139]

Welcome.

Have a read of the issues listed here first: http://w140.com/tekwiki/wiki/434

Usually I find these sorts of things are shorted caps. Look for tantalum capacitors and check them with a DMM on low ohms. Also the main filter caps tend to go at that age. Worth checking all semiconductors for open/short conditions as well as things tend to cascade fail. Visual inspection first of course!

Also to note, some SMPS won't start without a minimum load so this might not actually be the cause - could be a shorting tantalum or something elsewhere that is stopping the supply starting up when connected but also wont start when disconnected anyway.

[Jorge4563]

Wow quick response, excellent thank you. Here is a pick of the PSU.