Sequential Circuits Prophet-5 Service Manual - Audiofanzine

SECTION 4SERVICE4-0 GENERALThis section contains detailed service instructions for complete functional testing and for alladjustments. Instruments to be serviced should be thoroughly tested beforehand. This will verify amalfunction has indeed occured, perhaps reveal related or unrelated malfunctions, and provide a basisfor troubleshooting. The tests suggest trims v^hich may restore normal functions. If the problem(s)persist, you will have to rely on Sections 2 and 3 and your troubleshooting skills to locate the defectivecomponent(s).Throughout the functional tests you must play five different keys to test the five individual voices. Alltests are performed by ear; the object generally being consistency between the voices. There will alwaysbe slight variations between the voices. Ifsound.not excessive these differences help to "warm" the Prophet'sNote that while all tests can be performed with the cabinet unopened you will have to open the cabinetto identify the individual voices since there is no reliable way of identifying them by merely listening. Tocheck a single voice, GATE its or Final VGA output can be probed, or its relative volume manipulated(see paragraph 4-22). You may also be able to use the fact that the first voice assigned after the TUNEroutine is Voice 1.IProphet trimming is a sensitive procedure which as a rule should not be done more than necessary.Prophets are carefully adjusted at the factory, where many trimmers are sealed to preventmisadjustment by vibration or accident. You willrarely be able to make an audible improvement uponthese trims— unless a malfunction has occured or a part has been replaced. If you do try to ideally set all54 trimmers when no repairs have been involved, you may succeed only in correcting for the differencebetween our DVMs or room temperature and yours.Most trims require a 4-1/2 digit DVM. An oscilloscope (preferably, dual-trace) is required for filtertuning and for serious troubleshooting.These procedures are presented in the order recommended for a Prophet assumed to be 100%electrically functional but untrimmed. Real-world problems may require you change the order of sometests and adjustments. Therefore each procedure is written to be performed independently of theothers.4-1