Qbert 35V reads low

JDGJr

Member

Donor 4 years: 2012, 2016, 2019, 2024
Joined
Oct 27, 2009
Messages
659
Reaction score
8
Location
Longmont, Colorado
QBert powers up and plays fine, but knocker is silent.

Measuring AC voltages on the input side of the filter board, the 15V reads 15.8 and the 35 reads 19.5.

Any ideas where to start?
 
Will reflow the power board over the weekend, and rebuild the PS when your shipment arrives. ;)

Given those numbers, should i be worried about the voltages coming from the transformer assembly? The schematic shows that A12 J1 pins 1 and 2 should be 35V AC, and they're only 19.x, even with A8 P2 disconnected from the filter board.
 
Does it have sound? If so you know the 30v on the power supply is good. Next as mentioned would be to check for 30v at the fuse holder for the knocker and ohm out the fuse. Meter the knocker coil and see if its open. You may want to swap out the knocker transistor, its a 2N6044. If you dont have one check the schematics, there is an extra on the board that is unused that you can steal.
If you need parts I have complete knockers or individual parts for them.
 
It does have sound & the knocker fuse continuity is good.

I will check the other values tonite. thanks for the ideas!
 
IIRC, Qbert has a dip switch to disable the knocker......might just need to turn it on.

Edward
 
IIRC, Qbert has a dip switch to disable the knocker......might just need to turn it on.

Edward

For some reason I thought I had read he had the dipswitch on. Guess that was a different thread :) Yeah, first thing to check is the dipswitch.
 
Any pointers on how to do this? I would only get a reading when the knocker activates, right?

No, the +30 is always at the fuse. The knocker is negative triggered through the 2N6044 on the main board. You just need to put your negative lead of the meter on a good ground somewhere.
 
Got it! There is 30V to the fuse and to the knocker coil. Tried shorting the other coil lead to ground, and no noise. Removed the knocker assembly and now i can see that the coil is in fact open. Looks like that'd be the cause, and cause for another order!

thanks for the help!
 
No, the +30 is always at the fuse. The knocker is negative triggered through the 2N6044 on the main board. You just need to put your negative lead of the meter on a good ground somewhere.

So, i know there is 30V to the knocker. Is it a valid test of the knocker to touch the knocker's return-path lead to ground?

Also, my PS had only 1 of the 2200uf Caps - C21 was missing. What effect would this have on the game operation?
 
So, i know there is 30V to the knocker. Is it a valid test of the knocker to touch the knocker's return-path lead to ground?

Also, my PS had only 1 of the 2200uf Caps - C21 was missing. What effect would this have on the game operation?


Post a pic of your sound board.
Your power supply may have been modded for the sound amp piggyback board and probably only has around 18v on the 30v line. Its barely enough to work the knocker.
 
Here is the board (with new caps installed). please let me know if it is too fuzzy. BTW: the former owner said the knocker worked before he put the unit into storage.
 

Attachments

  • 2010-12-15 18.20.08.jpg
    2010-12-15 18.20.08.jpg
    85.6 KB · Views: 13
Last edited:
In process of rebuilding PS (waiting on parts).

I was just wondering what the effect of only 1 cap would be.

And wondering exactly how to test the knocker/coils. You mentioned 'ohm'ing the coil. my new coil shows the same readings as the old one, so I'm confused.

thanks
 
Finally finished rebuilding the PS - have a nice 5.05V at the chips, and a knocker sound when the machine powers up - rather a shock! Now to get the CP put back together and feel the knocker during game play.

Riptor - thanks for the great help here, and great service thru your store!
 
This is why I always tell people to rebuild the power supply and reflow the filter board before doing anything else to a problematic qbert. Glad to see you got it up and running.
 
Back
Top Bottom