HP34401A randomly displays incorrect characters on the display, won't self test

[TF567577]

Hi,

I had another HP34401A to repair and it's display was very random and it kept crashing. The picture attached shows it trying to display open. I replaced the display board and it still failed. The fault was eventually tracked to the ram U503. I found some M5M5256BFP-70L ics on eBay that worked.

Hope it helps

Cheers