Stargate
Gottlieb, 1995I need to replace C20 and C21 on a Gottlieb MA1934 CPU (for Stargate) which asks for 1uf 50v and on the board has a Tantalum capacitor installed. I was wondering if I can replace this with a 1uf 63v Electrolytic capacitor as I have these on hand.
Is this possible or do I need to order some Tantalum capacitors.
MLCC is probably a better option but electrolytic is ok too.
Later MPUs changed R5 and R6 to 680K which makes the watchdog less sensitive if you are having watchdog issues.
There is a better solution that leaves the caps alone.
Find it here:
https://www.pinwiki.com/wiki/index.php/Gottlieb_System_3#Beeping_and_Garbled_DMD
--
Chris Hibler - CARGPB #31
http://www.ChrisHiblerPinball.com/Contact
https://www.youtube.com/c/ChrisHiblerPinball - My YT Channel
http://www.PinWiki.com - The Place to go for Pinball Repair Info
Electrolytics tend to dry out (especially <10 uF values) and tantalums have a nasty habit of shorting and exploding, when they get old.
I really recommend using an MLCC ceramic capacitor. As a bonus, you can't install it wrong way around 
although some lead bending might be needed.
Here is the change Gottlieb made. Interesting the clamp to reset diodes never made it in the schematic but they did update the resistor value. World Soccer on left Shaq on the right. I think there was a service bulletin about it, but I can't find anything right now. I might have just read a blurb in a manual when it changed.
I imagine this resistor change would fix most boards that have watchdog issues.
barakandl
I've added the image and explanation you authored above to the PinWiki here:
https://www.pinwiki.com/wiki/index.php/Gottlieb_System_3#Beeping_and_Garbled_DMD
--
Chris Hibler - CARGPB #31
http://www.ChrisHiblerPinball.com/Contact
https://www.youtube.com/c/ChrisHiblerPinball - My YT Channel
http://www.PinWiki.com - The Place to go for Pinball Repair Info
This is perfect timing as I am also working on a Stargate MPU.
That is good to also know about the R5 and R6 values as I will also update them. This is a great pick up barakandl and thanks to
ChrisHibler for including this on Pinwiki.
I would also like to change the C20 and C21.
Would either of the below caps be suitable as I can get them locally just down the road.
https://www.jaycar.com.au/1uf-100vdc-mkt-polyester-capacitor/p/RM7170
This is a timing circuit so the tolerance matters.
Electrolytic caps suck for tolerance and change over time. Don't use those here.
Tantalum caps have a good tolerance but tend to be a bit pricey. They do have a bad history of burning due to excessive voltage but this is a timing circuit so shouldn't be a problem.
Ceramic caps used to be horrible for timing circuits due to wide tolerance and stability issues. They have changed a lot during the past decade or so. Get a modern ceramic with decent tolerance (about 5 to 10%) and it can be used here.
Polyester caps are inexpensive, have a good tolerance and will last forever. This would be my preferred solution for these. Get a decent tolerance -> 2 to 10% would be good.
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