Hey there Hachiroku,
nice to meet you, welcome to the group :).
On Mon, Mar 17, 2025 at 9:46?AM chester.jamie.jammy via groups.io
<chester.jamie.jammy@...> wrote:
Hi, my name's Hachiroku.
1.36V and -1.25V Ref tested OK according to this post:
/g/TekScopes/message/13732
I guess one other thing to check is whether J504 is in the correct
position, it should be jumpered between pins 1-2. If it's jumpered between
pins 2-3, it's possible that the DACs reference is bad, which would be good
as that's a well known, repairable fault that can lead to the symptoms you
see.
Here are the voltage measurements (reference to ground) at the DAC pins.
DAC Pin 14=0.151V
DAC Pin 15 =0.147V
More voltages:
Voltage drop across R2013 (10K)= 8.82V
Voltage drop across R2016(10K)= 1.02V
Voltage drop across R2011 (4.75K)= 0.639V
Voltage drop across R2014 (221K)= 7.97V
Voltage drop across R2015 (82.5K)= 8.18V
These all look reasonable.
It's a shame that I've decided to give it up as l observed different
Serial Numbers on different parts of the scope.
I don't think parts or PCBs were serial matched on these scopes, nor
generally in Tek instruments.
l assumed parts may have been replaced/repaired before by someone else.
Seeing how the NVRAM was missing, you know that someone was in there before
you, and without knowing the story it's hard to say whether the scope might
have e.g. been a parts donor. Usually it's reasonable to assume there's
going to be a single fault to fix, but with an instrument that's been a
parts donor, that may not be the case.
That being said, this might be as simple as some other fault on the A5
board or e.g. U950.
There might be some easy diagnostic steps you could try to see if you can
narrow this down, like do the HORIZ/VERT POS controls work and so on.
Have a nice day Siggi and thanks for helping.
No worries. I find it highly rewarding to get these old beauties working,
and every instrument I've repaired has been a learning experience for me.
If ever you decide to circle back to this, you might enjoy reading this
document: .
Have a nice one,
Siggi
