Re: Need to find 6 pin pcb transformer 120 to 12
- From: "Arfa Daily" <arfa.daily@xxxxxxxxxxxx>
- Date: Sun, 09 Mar 2008 10:56:42 GMT
<dnba@xxxxxxxxxxx> wrote in message
news:f89f2976-dbb1-41e4-a21a-b8bcc0e614b7@xxxxxxxxxxxxxxxxxxxxxxxxxxxxx
I am searching for someone that can direct me in replacing a powerIt is likely that an internal thermal fuse buried in the transformer's
transformer on a circuit board. A friend of mine asked me to get her
electric hospital bed working again. She recently had to be cut out of
a pick-up after a head-on collision and still needs an electric bed.
This is what I have so far:
The bed doesn't have a brand name but did have these numbers
handwritten on a factory checklist 97-85600 0010411 9-18-89
The control box has 2-MOT., 2-VIB. CONTROL BOX ASSY
PART NO: 5585550 / SERIAL NO: W0010411 (and also has a bar scan)
The circuit board has SCI-O-TECH 5201003
It has eight relays, all with 12 VDC coils
The transformer has PSC-244 EIA696B-8850 without any other info. It
is a six pin transformer mounted on the circuit board. There are three
spade terminals next to the transformer, Line, Neutral and Ground,
where the cord connects.
I measured 120 V at the terminals and found 120 V at the transformer,
but could not find any low volt output. There are no fuses. I don't
have a pin layout for any six pin transformer and need help finding a
replacement or another idea. I did try to find the board through a
medical parts suppier, but they could not find anything with the
numbers I gave them. I don't know who made the bed, which is why I
didn't get too far with the parts supplier.
primary winding has failed. This being the case, it should be an easy job to
measure the secondary of the transformer with an ohm-meter to determine its
configuration. I would expect the most likely to be a single centre tapped
winding, in which case, your meter will read pretty low ohms between all
three secondary terminals.
Have a look to see if there is a bridge rectifier, and two smoothing caps.
If there is, then the centre tap will be connected to system ground, and the
bridge will be producing a negative and a positive rail, with respect to
ground. You can get a pretty fair idea of the secondary voltage by looking
at the voltage rating of the smoothing caps following the bridge. Take about
20% of that voltage, and then multiply the result by 0.7. So, if caps rated
at say 25v, take off 5v = 20v and then multiply that by 0.7 = 14v, so
transformer would likely be rated either 12v - 0 - 12v or 15v - 0 -15v.
There may well be 12v regulators like 7812 and 7912 following the bridge,
and 20v input would be a good figure for these.
As far as current rating goes, that's really just guesswork and experience.
If the transformer is just powering some electronics on the board, then it's
unlikely that the current draw is going to exceed 500mA, assuming that all
those relays are not activated at once at any time, which I doubt, so any
transformer around about 6vA rating that's the right physical size to go in,
could be used. It does not *have* to be a PCB mounted type. It could be a
clamp mounted type screwed to the board, or elsewhere in the enclosure if
there's room, but if you do screw to the board, be very aware of any line
voltage tracks, and where your screws come in relation to them. Best to use
nylon nuts and bolts.
At the end of the day, it's not working now anyway, and it seems that there
is little liklihood of getting genuine service assistance with parts, so
you've got nothing to lose by having an educated go at replacing it. Worst
that can happen is that it gets a bit worse than it is now, which is all
part of the *fun* of this sort of project ... Hope your friend gets well
soon, and you are able to help her with this.
Arfa
.
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- From: dnba
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