Regardless of what was used before - there are right and wrong capacitors to use at C20 and C21.
Both of these two are part of the 74HC123 RC timing constant so maintaining some a somewhat consistent and proper capacitance value is important. Too low of value and the machine will reset when it isn't supposed to.

A ceramic capacitor most definitely CAN be used in this position. These caps typically have +/-20% tolerance - not real good for timing circuits. You can get these much tighter tolerance than 20% -- up to 5%. I'm willing to bet the originals were 20% caps. Just watch out for the inexpensive +80% caps -- nearly double in value for tolerance.

Tantalum caps also typically have +/-20% and can get as good as 5% but not many in the 5% range. You want the + oriented toward the connections to pin 15 and 7. Follow traces on board to figure out which solder pad connects to pins 15 and 7 and use cap's + connection there. C20 is easy to follow - the plus connection is near pin 16 of the IC. C21 - you need to follow connection on bottom of board. Looks like from above drawing that this cap installs in same orientation as C20.

Electrolytic caps -- do NOT cheap out and go this route. These start with a +80%/-20% tolerance and go down with age. Small value electrolytic caps are notorious for being the first caps to go bad in timing circuits and on sound boards.

If *I* were replacing this cap - I would go with a polyester film type capacitor. These are inexpensive and have tight tolerances. A cap such as a Panasonic ECQ-E1105JF would be ideal in this position. Long life, inexpensive, no polarity to worry about and tight tolerance.

Ed

_{Post edited by G-P-E : typo}