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Part Identification

davenn

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Sep 5, 2009
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Hey guys

my turn to ask a Q.

on an American made PBC I have parts labelled VR1, VR2 etc They are surface mounted look like and test like a diode. ~ 350k Ohms one way, many 10's MegOhms the other way.

other obvious diodes are labelled CR1 CR2 etc, which I am familiar with the "CR" designation

was wondering if the VR is a Zener Diode ??

I'm in the middle of doing some reverse engineering of the circuit in the hope of fixing a very common fault we get with these units that we have many dozens of in service around Australia. The manufacturing company isnt forthcoming with a cct diag not even a partial one of the part of the cct that is of interest.

cheers
Dave
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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It's not something like this is it?

Have you managed to draw a partial circuit diagram? Are these components protecting the inputs?

What package are they in, and do they have any markings?
 

davenn

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It's not something like this is it?

Have you managed to draw a partial circuit diagram? Are these components protecting the inputs?

What package are they in, and do they have any markings?

no not one of those :) its just a 2 "tab" package 4.5mm long 3.5mm wide, black, white band across one end marking LV with an S under that

ummm wouldnt be sure of the actual package type as in SO123 etc

ok here's the relevent part of the cct I'm working with
 

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davenn

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hey Steve,

ok remember that this is a partial cct mainly covering the PSU area and the printer port driver.
and I still have a wee bit more to add to it, like a ground connection to the negative of Bridge Rectif. CR2 ( a work in progress)

The main fault I get with these units is that they stop driving the printer port.
I'm suspecting the ADM485 and hopefully farnell is going to be able to supply some for me to trial on some of the faulty boards.

as far as my query on the forum is, is the "VR" designation, and if that was what our USA cohorts used as a designation for a Zener Diode

NOTE I have drawn them as a diode at the moment till I get clearer info :)

Dave
 
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(*steve*)

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I measured some unidirectional supressor (1.5KE400A1500W) diodes and they gave me between 64K and 3M forward resistance (depending on ohms range) and open circuit the other way. On the doide test they showed a forward drop of slightly higher than 1.3V

Something like this packaging?

Here are some devices in that package which are marked with LV.

If you can confirm that they break over at the voltage suggested by the datasheet, then it may be reasonable confirmation that they are what they kinda logically appear to be to me. That voltage rating seems appropriate to both the nominal input voltage and the maximum ratings for the regulators.

I can't see them being zeners as VR1 has no series resistance (and it's connected across a supply rail), and other diode types make little sense in that location
 

davenn

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hey Steve,

interesting, thanks :) that is the case style

they may well be some sort of surge protection as you suggest


now I have just updated the cct a little with a couple of corrections.

Note the 2 hanging off the + and - pins of the B-Rectif CR3 there is NOTHING else coming off those + and - pins there is ~ 3.2 volts on either pin under normal operating condition.

on the AC side of that B-Rectif. there is a digital signal being fed in from the ADM485 chip that goes via RT/FB 3 and 4 to the connector.
just for your info this feeds a remote 4 digit display. (not part of my prob.)

cheers
Dave
 
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shrtrnd

Jan 15, 2010
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Just adding some info. Unfortunately, manufacturers do what they want. Hewlett Packard marked their ZENER DIODES as 'VR', like you thought, for voltage regulator.
Typical HP designations for general purpose and power diodes is 'CR'. I would usually
assume finding VR on the board, designates a Zener. Since you seem to think your board was a product of US mfgr, I'd bet on it.
Good luck on the job.
 
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