There isn't really much wrong with DE machines but IMHO it is easier having machines that are the same brand and vintage - parts can be swapped around if something fails to assist with troubleshooting as an example.
JP is a great machine. Typical problems with JP is wear around the holes, side to side motor on the T-Rex. Other board issues have already been mentioned. There is also a common thought that the caps should be replaced as well due to corrosion underneath them which isn't seen until one fails and it is removed.
Good point on keeping machines alike, but I don't want to miss good titles having tunnel vision for say Williams.
Its great hearing titles I've never thought of, but have heard of, so now hitting IPDB.ORG to check out some pix. Keep the suggestions coming if possible
