Main > Monitor/Video Forum
Wells Gardner D9200 - Horizontal Collapse?
lilshawn:
higher voltage is okay. you typically spec a cap for about 2x the voltage... then the next closest working value up from that.
so for a 150v power rail, i'd spec out like a 350v capacitor (150+150=300) i'd probably only have a 300v, a 400v, or maybe even a 1000v in my bin and it would probably be completely fine to use any one of them... and for a 12v power rail a 25v cap. (12+12=24) and although it would be perfectly okay to use 16v capacitor...i'd probably spec a 35v cap anyway anyway since it's more common than 25v caps and the size difference isn't too much and it adhers to the "rule"
the rating is often fairly overspec'd for it's labeled working voltage anyways. it's basically the rating the dielectric insulator breaks down and allows current to pass through it unimpeded. chances are, a good cap will (albeit unhappily) take 2x it's rated voltage before ACTUALLY breaking down... it would probably change it's value much sooner running it constantly over voltage like that... but even factoring in your back-of-the-napkin estimates of doubling the working voltage of the circuit, you are really in the 3x neighborhood of being overspec'd anywhos.
i think that rail maxes out at like 195 or 212v? something like that? depends on the resolution... but i think a 250v is probably perfectly fine... it doesn't adhere to the 2x "rule" per se, but is still within the working voltage it's rated at... and probably why someone changed the part list to say 450v
Rocketeer2001:
Ok, good explanation! I picked out a 400V one. They had a 250v, but it was oddly tiny in physical size, and they had a 450v but was also tiny. The 400V one was the closest in physical size to the old one, and had all other specs matching what I needed.
When the parts show up, I'll get them installed and report back.
Thanks for the help so far everyone!
Rocketeer2001:
The new parts arrived in a day, so I installed them today in the board and put everything back in the arcade cabinet. Turned it on and for a split second it seemed like it was working! But then I saw that new Q418 horizontal transistor sizzle around it's edges and the heatsink with electricity, then the whole board let out a horrible screeching noise and we're back to collapse.
I'm thinking whatever part broke the original HOT has now cooked my brand new HOT. Or my new HOT was faulty, or the new C455 capacitor was faulty, or something else?
grantspain:
what heatsink compound did you use and insulation sheet?
lilshawn:
check D416 and D417.
and yes, you should be using a mica sheet and silicone heatsink compound.
the hot must be isolated from the heatsink.