The PU620 is the module that produces the waveform (~1.2-1.5 kV) that
charges the capacitors used to pulse the flashlamps in an old
Quantel/Continuum YG681--the laser in question. This is an old laser, but
Continuum tells me that a modified PU620 is still used in some current
Continuum products. What they refuse to tell me is anything whatsoever
about possible troubleshooting procedures for any PU620 of any vintage.
When I asked what components, based on past experience, usually are the
ones that fail, they say "could be anything". Perhaps some readers of this
message have corrected problems in PU620 (or PU610) modules of some
vintage. Also, other YAG lasers may have fairly similar modules with
similar causes of failure.
PU620 in brief: The main analog board uses a reactance-limited dc-dc
converter to provide a controlled charging current to the capacitor bank
(capacitors in another module). There is also a digital control board in
the PU620. It has to control the charging enable/control for the analog
board, and has some shutdown failsafes.
OUR PROBLEM: In the most salient--completely vague--description, the
flashlamps are not flashed. We were able to borrow a similar PU620 from
another laser and then the flashlamps flashed properly. We do have circuit
information in the original YG681 manual for both the logic and analog
circuitry. IF one could follow the schematics on an electronics workbench
and make appropriate measurements with the PU620 in similated operation
(but not embedded in the laser control rack), it would probably be
reasonably straightforward to find the likely fault. For the HV part there
would need to be appropriate safety protocols. However, it's not clear how
to do any of this on an electronics workbench, with the module disconnected
from the rest of the laser. The manual contains only schematics, no
suggested procedures, and Continuum will not provide any help/information.
There are probably a number of effective tests on discrete portions of the
logic and analog circuitry that can be done fairly easily, but Continuum
will not supply any information.
Does anyone have suggestions relating to one of these areas?
1. Components most likely to have failed.
2. Any sort of an electronics workbench approach to trying to find the
problem.
3. Suggestions of any place or individual who might be helpful in carrying
out diagnosis and repair.
Thanks!
Mark Sulkes
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