Dating from around 1989 a piece of test gear that I imported from the US at great expense about 12 years ago. I recently dug it out to try and it was failing it’s self test. The calibration values are stored in non-volatile RAM, which is a memory chip with built in battery.
The repair was successful, although the specifications and size of this machine are pretty dated when compared with my modern Rigol scopes.
Taking the scope apart and removing the main board:
This is the original Dallas NVRAM. I desoldered the chip and put a 28 IC pin socket on the board. Fitted a replacement chip, which was a cheapo Chinese eBay special, so not sure of its age. However the chip socket will make future replacement simple.
On power up. The scope started rebooting at random intervals. So I took the power supply out and checked some of it’s output capacitors. Two were found with very high ESR values and a further one with slightly high value. All were 220uF 50V. The other capacitors tested ok. There was some electrolyte leakage from the worst caps. And slight board damage. So this was cleaned up:
New capacitors fitted:
After a reset and restore to default calibration, all the self tests passed:
Finally the calibration routines were done: