What is at RV1 on Star Wars main PCB?

Kaboom

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There isn't much of a description in the PDF manual, and the schematics only refer to RV1 as a "VDR" and the PCB component list only list it as a "nylon snap in fastener."

The one on my PCB is missing and probably part of the cause of the problems I am having with the game. Can anyone help me identify what this part is so I can find a replacement?

Thanks!! Picture of above on my PCB is attached!

Greg
 

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"Nylon Snap In Fastener" sounds like the nylon standoff to support the sound board off the main board. I doubt that'd cause any problems gameplay-wise unless your sound board is just hanging there laying up against something.

DogP
 
Oh... heh, I didn't see that the first time I looked at the pic. I thought it seemed odd that they'd give that a component name. I just looked at the parts list... I think you read the wrong line... it says RV1 is 8 V Variable Resistor. It looks like your RV2 is still there, which you could look at (should be the same part). It looks more like a Varistor than a variable resistor though (a variable resistor would be a potentiometer... it doesn't look adjustable, and why would it be 8V?).

Maybe something like this would work:
http://www.mouser.com/ProductDetail...=sGAEpiMZZMuQmL5N8IqpX85aaY//zQae3fR3k/8vSqA=
or
http://www.mouser.com/ProductDetail/Littelfuse/V18MA1A/?qs=slssyL07VvNT7RADKzu3Cw== .

Ah... yes, looking at the schematics, it shows it as a VDR, which is a voltage dependent resistor, which is a Varistor.

But that shouldn't cause a problem with your board by not having it there... I'm guessing that's to protect either the TL082, or the monitor from excessive slew. In normal operation, it should be open.

DogP
 
Oh, man am I a goober. It's on the AVG board, not main PCB- 8V variable resistor, doh.

Yeah, well my monitor picture is partially skewed- letters & vectors climb to the right making the picture awful.

Neither of those parts looks right...but thanks, I'll keep searching...
 
Oh, man am I a goober. It's on the AVG board, not main PCB- 8V variable resistor, doh.

Yeah, well my monitor picture is partially skewed- letters & vectors climb to the right making the picture awful.

Neither of those parts looks right...but thanks, I'll keep searching...

Don't change it out- it might be fine.

It's supposed to look like that. In the lower left of your pic you can see RV2 for the Y channel. My Tempest has the same odd looking part.

And no, it's not an MOV of the circuit protection kind. Way too small. I'll try to figure out what it is exactly.

Ok, on Tempest it's there to clamp the video deflection to 8 volts to protect the monitor.

Chances are good if it went bad you'd be looking at squished, not strecthed images. Your culprit is the associated TL082 or the multiplier chip just before it (I'm going by the Tempest schematics but star wars must be similar.)

Check your +/- 15 volts in the analog section too.

Edit: followup data; I'm wrong about the purpose of RV1. It's there to nullify a CRT nonlinearity. Without it, you don't get strait lines on the screen. I'll be tryingbto track down a replacement.
 
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Did you ever find a source for the RV1 & RV2?

Don't change it out- it might be fine.

It's supposed to look like that. In the lower left of your pic you can see RV2 for the Y channel. My Tempest has the same odd looking part.

And no, it's not an MOV of the circuit protection kind. Way too small. I'll try to figure out what it is exactly.

Ok, on Tempest it's there to clamp the video deflection to 8 volts to protect the monitor.

Chances are good if it went bad you'd be looking at squished, not strecthed images. Your culprit is the associated TL082 or the multiplier chip just before it (I'm going by the Tempest schematics but star wars must be similar.)

Check your +/- 15 volts in the analog section too.

Edit: followup data; I'm wrong about the purpose of RV1. It's there to nullify a CRT nonlinearity. Without it, you don't get strait lines on the screen. I'll be tryingbto track down a replacement.
 
I'm going to dredge up this old thread as I am looking for a replacement for RV1/2 on the Star Wars AVG boards and am having a hard time figuring out exactly what I need. Anyone have a compatible part #??
 
I'm going to dredge up this old thread as I am looking for a replacement for RV1/2 on the Star Wars AVG boards and am having a hard time figuring out exactly what I need. Anyone have a compatible part #??

Looks like I found my answer... and it's a NLA custom part.

http://www.biltronix.com/Space_Duel_to_Major_Havoc_Conversion_Board.html
About the "VDR":

The original Atari VDR (voltage dependent resistor) located on the board at location R24 was a custom made semiconductor. It was a specially doped silicon carbide wafer with leads attached to form an axially mounted resistor. This resistor has an unusual property in that its resistance value decreases exponentially as the voltage applied across the component increases. The non-linear response of the VDR was used to create the "linearity" adjustment that allowed the operator to calibrate the straightness of the diagonally drawn vectors. The VDR was used on the Space Duel and Tempest to Major Havoc converter boards and also on many of the game boards such as Space Duel, Black Widow, Gravitar, Major Havoc, Star Wars, and probably several others.

The original Atari VDR component is now very hard to come by outside of the game boards themselves. There is no modern equivelent that I am aware of. While there are plenty of so-called non-linear resistors available in the form of over-current and over-voltage protection devices (referred to as polyswitches, polyfuses, and MOV's), none of them lend themselves to the application of linearity adjustment. This is because they are all engineered specifically for over-voltage or over-current protection. Modern components are made from Zinc Oxide that has a very sharp turn-on response. Also, the turn-on response usually occurs at a voltage that is too high to be useful in the VDR application.

With no supply of original or equivelent VDR components available, I had to create a substitute circuit (BXVDR shown below) that provides the same resistive response as the original Atari part.
 
I wonder if you contact him directly, or if he is still here, if he would release the Schematics for that little board.
Or maybe make a small run of just those.
 
I believe from looking at it, you can determine the schematic.... other than the values of the resistors.... not sure if '5C' is an identifying enough mark to determine the transistors used (I don't know surface mount).

Looks like as the voltage ramps up, it must fire more and more transistors lowering the resistance as it happens. Though I don't know if it ramps smooth like the original part, or more like a stepping type of 'curve'.

Hopefully Bill can share. It is an interesting replacement solution.

Maybe if we're all lucky someone will find a parts bin full of these some day :) Along with bins of the sega G08 custom chips, some original Atari AVGs, etc :)
 
Bill will surely help you out, he's just a busy guy, and sometimes takes a bit to respond.

Also, his current email is bill dot earthlings at gmail (dot = period), in case you want to verify.

I agree, the community could use a standard replacement for the VR's on Atari vectors (whether it's Bill's solution or otherwise).
 
Yep, that's the email that his web page fed me. Thanks for confirmation. I don't expect immediate responses from folks. We all got stuff to do.
 
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