Re: [ukvac] BATTLEZONE Tech question
Okay, heres the jist: The diodes are 1N100 'switching diodes'
Anyways: the plot thickens:
I have a few boards with the same PN number: 035742-02 - but there are
differences in the build/layout, designated by a revision code on the
upper-right-hand corner by the loom PCB edge-con. I have rev A and rev C
boards.
On a rev A bd - there is no CR12, but on mine, there is a Hack on the
board which adds the same component as CR11 to protect the VR3 +15 line.
And CR12 is not listed in the Operators Manual Componenet list (3rd
printing issue), but does list CR11 as 1N100.
On a Rev C bd, CR11 & CR12 are fitted with identical components, but: the
position where CR11 was denoted on rev A is now labelled CR12 on a rev C
bd. CR11 has been added underneath the VR2 regulator. CR12 and CR11 are
shown on my schematics (Sheet 2 Side A) and match the boards:
specifically: CR12 is connected the +5VDAC line (VR2) and CR12 is
connected to the -15V analog power line (VR3) and both are designated as
1N100 on the schems.
So, CR11 = CR12 = 1N100.
CR11 & CR12 are 'crowbar' diodes to protect the regulated power lines from
either going the wrong way or over the diodes voltage limit. (all the
other CR diodes - except CR2, are virtual-earth protection diodes on the
op-amp inputs, CR2 being the Power LED). So CR11/CR12 clip the power lines
to 0.6v or so if ther 'go the wrong way' ie: the +5v line goes negative,
of the -15v line goes +ve. If the powerlines should exceed the voltage
rating of the diode, in this case, the diodes are 100V 'switching diodes'
(according the schematic and handbook parts list) 1N100 diodes (Atari PN:
31-1N100). So if the lines go over 100volts they will conduct. As the
lines shouldn't ever really exceed the power-in to the regulators (+/-22v)
this mode is never really used. So all they do is conduct if the lines go
the wrong way. Otherwise they do nothing and can be replaced with just
about any equivalent 'reasonably strong' and fast diode - my guess would
be a 0.5 to 1watt switching diode, but as they are fail-safes, you might
get away without them...?
Gud luck - chrz - Tim.
PS: Anybody got any spare BZ stuff they want to sell/trade? Anything
cosidered!
ygroups@ektr.com
Sent by: tim@ektr.com
10/09/2004 23:35
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Subject: Re: [ukvac] BATTLEZONE Tech question
I'll take a look in the morning and let you know.
I think CR's are power-supply crowbar diodes - have you checked all the
schem drwgs?
(But if its not on the schem - you might be able to live without it!)
Chrz - Tim.
"urban_paranoia" <urban_paranoia1@btopenworld.com>
10/09/2004 17:54
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To: <ukvac@yahoogroups.com>
cc:
Subject: [ukvac] BATTLEZONE Tech question
Hiya
Anyone know what type of diode is at location CR12 on Battlezone main
PCB's?
It's absent from the Schematics/Parts lists I have access to...
My board sez A035742-02 Jan 1981
Cheers
Alan
)
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