DIYbanter - View Single Post

George Pontis

wrote:

George Pontis wrote:
Hi Group,

I've got a 54540A in need of repair. This is a 4
channel 500 MHz digitizing scope of the generation
before Infinium. When first turned on it appears that
nothing happens. But it is alive to the degree that it
recognizes if you hold down a key during power-up,
which is the signal to prompt for a firmware update.
In this case a prompt appears on the CRT, and you need
to confirm with another keypress if you really want to
read in new firmware. If I press another key (even
though I don't have a new disk for it), then it
appears to go dead again.

I have a 54542A with exactly the same problem. I first noticed it
after a nearby thunderstorm, although it had been plugged in but
switched off at the front panel, so that may be coincidence. It
happened a few months ago. Could it be a date related boot code bug?
If so, maybe resetting the calendar chip (by disconnecting the
battery) might help? Maybe the lithium battery has discharged and it
can't run without it? Maybe there is a corrupt flash/eprom memory?

I do have a couple of firmware floppies, v1.30 and 1.50 (16 March 94).
More recent firmware exists (with improvements to the FFT code and
perhaps more), but I have been unable to obtain it so far.

If I do a button-pressed power up, I get to the point where it asks
for the shift key to be pressed to reload firmware. When I press it
with a floppy inserted, there is no sign that the scope attempts to
read the floppy. The floppy led does not light up, nor is there any
sound of head seeking.

I would really like to get this working again. I looked at the
diagnostic flowchart in the service manual, but this situation is
simply not covered. I haven't opened it up yet to check the psu
voltages, but that is the obvious next step. I somehow suspect that
they will be fine - but maybe the lithium battery will be interesting
to measure.

It would be nice to get a copy of the schematics.

John Walliker

With some effort I was able to get to the lithium cell, and found that
it had dropped to 200mV instead of the 3V nominal value. I shorted it
out momentarily, then connected a couple of alkaline AA in parallel
with it. The scope powered up right away!

The downside is that all calibration info has been lost. The scope is
visibly in error with the default values loaded. Oh well, it should be
easy enough to calibrate since most of the volatile parameters seem to
be DC effects.

FYI, the battery is marked "Sanyo CR17450SE". It is an A size cell with
radial leads, 3V / 2500mAH.

--