16 Jun
2014
16 Jun
'14
1:12 p.m.
All,
I have an (untested) H7140 here with the bias/interface module from my
dead one...took me a bit to get it in...apparently the aligning rails got
knocked loose.
Now, it comes up ad the DC OK light blinks (there is no load, I haven't
done voltage checks and I'm not ready for a load yet). However...the fans
don't spin and I measure 0VAC there. Last night the wires had gotten
caught on something, cut a bit and ended up shorted together...I hadn't
noticed as the tag covered up the damage...but I fixed that today. I
wouldn't imagine there was protection missing there...I never heard
arcing, anything frying, and I didn't see current draw shoot up.
Any ideas? I don't want to put ANY load on this until I have the fans
working...not even a dummy load.
YEs...
The H7140 is a bit strange. No, let me put that anotehr way. It's
totally uncovnentional.
The first thing is to have a clear idea od the secions of the PSU :
Incoming mains is rectifieed/smoothed to give about 350V DC This supplies
3 other secisons
There is a little SMPSU (of a fairly conventional design) to provide the
power for the cotnrol circuitry. The transformer is on the packplane
board, the chopper and control circuitry are on the bias/interface board
There is the 'logic' suppky. A fairly normal SPMSU with all control
circuitry o nthe output ( not mains) side of the isolation barrier. This
supplies +5V, +/-15V for the lgoic
Lastly there is the meory supply. This is another SM{SU (of a similar
design to the logic PSU) that provides 36V. This 36V can be
battery-backed. It is then regulated down to +/-12V and +/-5V for the
memory boards usign non-isolating switchign regulators.
Now for the fans. As is well-known these are special, 35V 70Hz ones. They
are run from the 36V DC rail i nthe meoroy supply via a full-H driver
circuit (4 power tranisotrs on the bias/interface board) and associaled
bits. The idea of that is that the fans are also abttery-backed.
Now, there is no protection on the fan driver circuit. So any short
between the fn leads of fro ma fan lead to chaiss will do damage. In
particular it burns out the transisotrs i nthe full-H circuit.
I would start by checkig nthat 36V supply is presnet and correct. There's
a capactior on brackets conencted to the 2 boards in the memory supply.
Check acoross that. TAKE GREAT CARE when working on this PSU, the
rectified mains is carried on some of the barrier strip blocks on the top
of the PCBs. And it is iethal. Seriously lethal. before touchign anything
i nthe PSU, swithc off, pull the mains plug, wait a few minutes, then
cleck the ovltage beween the wires on the 2-way pbarirer blocks. Only
start woking on things when that voltage is too low to be dangerous.
If that 36V supply is fine, then check the 4 apporpriate transsitors on
the bias/interface board. Most likely soem are damaged.
-tony