16 Jun
2009
16 Jun
'09
5:12 p.m.
Keith Monahan wrote:
So in my hunt to find more information on switches I want to
clean/replace(that was mentioned in another thread), I took this Brian
Instruments Brikon 723 floppy drive analyzer apart.
I've taken my share of equipment apart, but I can't believe the size of
the components inside. Can someone help me make sense of this design?
I find no fewer than 4 HUGE transformers:
(2) Pacific 0288 DP100-16
(1) Pacific 0288 DP100-28
(1) Pacific 0388 DP30-36
There appear to be (7) terminals on each transformer. Maybe +,-,GND on
the primary AC side, and then (4) terminals on the secondary DC side?? I
guess all (4) terminals would be the same voltage?
I've emailed Pacific for the datasheets --- I doubt they are current
products.
Then, there are these huge capacitors, (8) Frako 3300uf ones.
There are about 20 leds and 20 switches on the front panel, which are
not easily accessible from the back side. The front panel has a half
dozen 7-segment LEDs.
One of the more prominent socketed chips is a Burr-Brown DAC80-CBI-V.
(http://www.datasheetcatalog.org/datasheet/BurrBrown/mXrvxzt.pdf)
There are a few daughter cards with a bunch of 74LS logic chips. There
are other ICs that I can't get to without going deeper into the teardown.
There's a decent size fan on the back of the unit for cooling.
I guess I'm at a loss for the transformers. Why 4? So that you have
separate stable sources of DC power so that the pull from one doesn't
affect the others? Can I replace the power circuits with something
smaller and newer?
The transformers and caps make up easily 1/2 the total size inside the
chassis and easily 75% of the weight.
(Pictures are always nice for making such assessments. ("HUGE" may
be quite relative to one's experience.))
The number of transformers may have been simply a manufacturing economics
issue. A floppy drive analyser is going to be produced in relatively small
numbers, and they may have chosen to use 4 off-the-shelf types rather than
having one special transformer specced and manufactured. Maximum physical
dimensions might even have been an issue. If it's an early analyser
targetting 8-inch drives as well as 5-inch, one of the transformers is
probably to supply the 24V that some 8-inch drives required.
The -16, -28, -36 are probably the secondary voltages.
A guess might be: one -16 split-phase rectified for the 5VDC logic, one -16 for
12VDC to the floppies, the -28 for 24VDC to 8-inch floppies, the -36 is weird
but it could even be dual-half-wave rectified for +/-12VDC for the logic if
such is required internally.
8 3300uF caps doesn't sound excessive for several linear supplies, some of them
are probably parrelled.
Regarding the 7 terminals, one possibility is they have dual primaries for
120/240 VAC operation. That would eat up 4 terminals, leaving 3 for
center-tapped secondary or 2+earth(shield).