Look for the manual on the WWW.
Open the drawer just below the Meochrome Color head and take out the diffuser glass.
Check again on the contrast.
Also check the voltage output of the transformer.
Check if the bulb you changed has the same spec's as the original bulb.
The Meopta 5 with the Meochrome color head should give you very good results.
Also check your enlargement lenses.

Best regards,