2465A battery backup - 2465A SRAM Failure


I just finished replacing the Battery, rebuilding the Power Supply, broken Scale illumination Pot on a 2465A for one of my nephews. It had an SRAM Failure that I had to replace. The Failure was internal to the D4464-20 SRAM. The Address Line A01 opened internally inside the IC. Odd failure, entertaining to track down. I doubt that the Battery dying damaged it, I'm guessing it was a metal migration issue inside the package.

The failure shown was that the Scope would not pass the Calibration and failed Test 04. It would pass all of the manual and automatic calibrations steps, but would not Power-on with a passing Calibration.

I performed several Calibration cycles (many frustrating hours - it should have worked, right), before I decided to figure out what was really wrong. I found it because the data in every other address on Exer 02 was garbage. I surmise that each time it checked the Checksum for the SRAM contents, it was wrong and would fail that.

Luckily, the D4464-15 devices are still available. When it was replaced, it behaved correctly and I was able to complete Calibration, check functionality and button it up.

Hope your SRAM Failure was easier to find.


-----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of amnesia
Sent: Friday, May 20, 2022 12:39 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] 2465A battery backup

Ahhhh, that makes more sense! I too hate the butane iron. I ruined many a board until I bit the bullit and bought the Hakko. Always looking for a good reason to use it.

Interestingly, I bought it to replace a battery backed up RAM chip in my prized pinball machine with what the pinball world calls NVRAM - truly "non-volatile", no battery required. Would be great for old Tek scopes, but unfortunately there's no way to get the data over to the new chip, so you would still need to recalibrate it - but only once, and never again.