What would cause a fuse to blow every 100 or so startups?

[brad808]

So on my Hollywood Heat (Gottlieb system 80b) every once in a while, maybe 75-100ish times that I turn the machine on it'll go a little funky. Sometimes I'll get a bunch of weird characters on the display and it'll blow fuse f11 which is for the drop target reset coil. It's not a huge deal because I have a box of fuses I keep in the machine and I can change it from the coin door but I would like to try and sort out what would cause something like that. After I change the fuse, turn the machine back on it'll work perfectly fine and remain that way for another bunch of times I cycle power and then bam it'll happen again.

Any suggestions on where to begin trouble shooting a problem like that? All the ground mods appear to be done on the machine and the power supply seems to be giving out the right voltage (at least when it is on and operational, not sure about start up spikes?).

Thanks in advance for any help.

 

[sylvain]

Re: What would cause a fuse to blow every 100 or so startups

1st thing I would check - make sure that the voltage arriving on the MPU (from the power supply) is +5.0-5.1 volts.
Adjust the pot on the power supply regulator heatsink if needed.
Also check for any possible cold solder joints under the regulator heatsink board.
Gently tap on that heatsink regulator board and see if you can get the issue to occur.

Also make sure that the power cable and connectors between the power supply / regulator heatsink and MPU are secure
and making good contact (e.g. wiggling that cable while the machine is on should not get the machine to stop, freeze or reboot).

Next step would be to check the AC ripple across the large filter cap, to see if it needs replacement.

Good luck !
- Sylvain.