new member, first post and a pleasure to meet you all - the problem i was having is resolved, but i thought i'd post it for future reference
i replaced the bulb on this unit, cleaned the machine out & reset the lamp timer - but the customer called back saying the machine was overheating and turning off after 5-20 minutes
so i dismantled the machine, cheated the interlock and left the top cover off to check fan operation - all 4 fans were running, yet the lamp temp kept climbing til shut-off - as i was fluffing around i happened to look through the lamp exhaust fan at the light source and i noticed the exhaust fan was turning slower than the other fans of the same type, so i swapped out the exhaust fan with the power supply fan and no more overheating
replaced the fan and now all good
