I've got an SSW2000 repair that seems to be turning into a science
project.
The customer bought it cheap off Kijiji. It didn't 'go'.
I found all 10 of the 30A automotive fuses blown, suggestting that
the last thing done to it was a reversed battery connection.
None of the DC inverter fets were damaged - This section proved to
run when a normal downsteam load was present.
The two main HV bulk caps were dried out and had vented oton the
wrapped heatsink. This over a long enough time period that the
vented material had collected air fluff as it dried.A small spot
of vented material had been deflected onto the LV driver control
board, bridging board vias and requiring scrubbing w alcohol to
remove.
One side of the inverter bridge was shorted through the switching
fets. When replaced, the recapped inverter ran normally under
lighter loads (below 500W).
I might mention that one of the unit's fans was dead, as well.
There is a small visible nonlinearity in the negative-going
sine output 'increasing' edge, which looks increasingly like
undamped response as load increases. This (negative generating
pwm) was the side of the bridge that had failed previously.
At some point of increasing load, the negative going sine
output flat-tops - coincident with the positive going side
cutting out completely on its falling edge, then the unit
latches off to an overload limit.
I'm not sure if this performance is aggravated by the loading
method - resistive through a variac, so any DC imbalance can
result in largish mag current imbalance.
Input to the low frequency AC limiting circuit seems normal,
though it is designed with a ridiculously high impedance -
a multimegohm RC filter from a 70milliohm sense resistor -
possibly to cut down on C size. It floats on the swinging
polarity of the negative bulk caps. Even some of my go-to
diff probes leak enough to make this a 'hands-off' test point
while in operation, but what I can see of larger signal stuff
at 50:1 diff looks normal.
There are no schematics available for the 3x control cct boards,
which are basically 339s and 324s working with schmitt triggers
and flip flops. Gate drive is optoisolated x4 with DC restored
bootstrap power on each. LF AC reg (tl431)and fault signals are
optoisolated
A main board schematic is available on groups.io in Electronics101.
This shows that any control cctry components on the main board
are basically concerned with fan control or external comms.
Red detail indicates modifications not present on production
(this) units - again mainly fan control.
http://ve3ute.ca/query/Samlex_SSW-2000_main_board_schema.pdf
Any ideas or similar experience out there?
RL
Housekeeping supplies are reverse polarity protected, simple
and solid. AC voltage output LF amplitude is well regulated.
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