17 Jun
2014
17 Jun
'14
3:04 p.m.
The H7140 is a bit strange. No, let me put that anotehr way. It's
totally uncovnentional.
That I know for sure. ;)
The first thing is to have a clear idea od the
sections of the PSU :
Yeah, that helps.
Ahh. Logic starts on the module where I don't know if it's good or not.
It is meaningless IMHO to regard the bias/interface board as one module.
It contails 3 parts of the PSU circuit, which are mostly independent of
each other :
The control cirucit and chopper for the PSU for the control circuits fo
the main PSUs . Be warend that this PSU is fairly conventional and as a
result much of the circuitry is on the live side of the isolation barrier
-- directly conencted ot the mains. Take care
The logic that eneables/disables the 2 main PSUs depending on the console
switch, etc
The fan driver circuit.
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.
Ahhhh! Also on the bias/interface board! That module might very well be
bad...which would explain a lot of the problems. 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.
Ahh. I imagine they're not uncommon power transistors? Can you give me a picture of that? I'm having
difficulty visualising it
in my head for some reason...all the wires confuse me a bit...but when I
know what's what I'm good.
On the top of some of the boards are little spade terminals soldered to
the PCB. These are fitted to plastic screw-terminal blocks, the design of
these blocks iwth braised barrier ridges between the screws leads them to
be ca;lled 'barrier strips' in the UK. I am not sure what they are called
elsewhere.
In genneral, in this PSU, these are used for mains-side voltages. Briom
what I remembrer at least the 'logic inverter' (==chopper) PCB has a
multi-way one goign to the chopper transformer for that supply. And both
the 'inverter' boards have 2 way blocks with wires going to the big
capcitors at the left side. These carry the 350V DC from the maisn
rectifier/smoothign capacitors to the choppers. Needless to say that is a
lethal voltage/current (and the connections ot the hcopper transofrmer
migth well be deadly too).
Before workign on the supply, unplug it fro mteh mains. Wait a few
minuts. Then take the cover off (if it's not already off) and measure the
votlage between the connecitosn on one of thse 2-way barrier strips. It
doens't matter which one, they are the same. DOn't sart disconnecitng
things or pulling PCBs until that voltage is too low to the dangerous.
-tony