Dear WFD group,
As you know three of us(Kearns, Orth, Walter) spent a few weeks tuning
up the WFD system at the GS after the last meeting. Among other
things a bad back-plane was fixed on SM1. However after putting the
system back together we are still experiencing some strange problems on
SM1. Please let the WFD list know if you have suggestions. I am
especially interested in hearing from the people at TAMU who are
familiar with the power supplies.
There are more or less two problems(although they may very well be
related.)
First of all, after everything was put together, we found that SM1 was
only able to run in the real acquisition if we used a VMDIS/VBR. In
otherwords, if we try to use a VIC-8250 in SM1 then we get VME errors
when we try to run. The strangest part about this is that you can't
see any errors if you are using the stand alone program. You can
write to every channel, set the thresholds, read out data and it is
fine. But when you try to run in the real acquisition you get VME
errors.
So, for right now we plugged in the VBR/VMEDIS combo. However, that
isn't the end of the story. Things seem to run fine now *EXCEPT* that
it seems after the microvax has been rebooted when a run starts for 10
or 15 minutes we get VME errors. During this period the voltage on
the backplane drops from 3 Volts down to 2 Volts. After the voltage
goes back to the normal 3 Volts the VME errors go away. The errors do
not happen on every event, nor does every channel always get an error.
This is *not* a problem associated with the start of the run since
normal run changes don't have this problem it seems to only happen
after the microvax has been rebooted. In addition the problem is not
related to cabling since the cables to SM1 and SM2 were swapped and
the problems did not move.
Here are some things we know(or should find out):
o This crate has the north face card so draws slightly more current
then most other crates.
o The voltage on SM1 is somewhat lower then it should be. In the past
it has been 15-20 Volts to low. This has caused problems on the
Lecroy HV supply on SM1.
o How would the power supplies react to this low voltage?
o Is there anything that happens on the VIC bus when a microvax is
rebooted?
If you respond to this note reply to the list not to me(ELM users can
use "g" instead of "r").
- -Chris
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