Response from Jonathan: Bill,

> We took the old power supply board out of the equation and ran the power directly to the switch and to the board and monitor.

> When powering up, the board boots and we get sound but the monitor will not power up. The monitor has a tag mentioning an insolation transformer. Could that be our problem?

Yep, this is probably your issue. Older monitors such as the Wells Gardner K4903 require the power they receive to go through an isolation transformer. The isolation transformer looks like a big brick in the bottom of the cabinet and usually has an AC input (usually 2 wires coming in the bottom of it) and output (usually 2 wires coming from the top of it). Our friend Bob Roberts has a great article on his web site that discusses transformers if you would like more information on what they do. Here’s a link: http://www.therealbobroberts.net/xformer.html

With that said, you probably blew some diodes on the monitor chassis (if you did in fact hook the power up to it directly from the wall). Check out the diodes in locations D501-504 and replace as needed. Hopefully no other parts blew on your monitor chassis but definitely want to start with the diodes first and see if that solves your issue. Make sure that you hook the isolation transformer back up before trying to power on the monitor again or else you’ll have to repeat the diode replacement process.

Also, highly recommend spending some quality time with our blog posts, videos and podcasts. In fact, we actually have a post where we discuss this exact problem. Check out Checking Diodes On An Arcade Monitor for more information on the process I’ve described above. Keep in mind we also have DVDs for sale that have additional videos that might also help you out. You can purchase them from our online store at http://www.arcaderepairtips.com/store/.

Hope that helps. Thank you for your question and good luck with your repair.