On the old Bally games. LED’s work in all non controlled lamps. But, all the controlled lamps you need either a new style lamp driver, or an anti flicker kit that easily installs to the original lamp driver. This will eliminate the LED flicker on your controlled lamps.

https://www.cometpinball.com/products/bally-stern-flicker-eliminator

This is the easiest and (not the cheapest) way I have found. Works well, and their warm white LEDs look great too if you ever need a source. Great company to deal with. Plugs right onto existing lamp driver board in between existing pins and connectors. Still won't break the bank at $30 and it will save you the headache of soldering each socket.

The absolute cheapest way, literally pennies, is to add a resistor to the bulb socket. Might take an hour or two, but prob $2.00, and you probably have some laying around. Search the forum, there's pics of where to solder it.

"No Joy" means the LEDs didn't light at all?
If so, you might have installed DC LEDs wired for the wrong polarity, or the bridge rectifier for the insert lamps on the rectifier board is faulty.