Tips: I stock key bushings to get rid of the clatter that is becoming prevalent in these units. Any silicon based lube is good on them but the rubber is disintegrating at this age. Switches need replacing or cleaning often also. Power supply problems were common especially in earlier versions I hear. Version numbers are in huge letters on the CPU board. However we also see upgrades installed when a 6116 SRAM chip is in IC14's socket, and a chip is piggy backed with IC9 nearby; a version 3.3 upgrade.
Knobs:
Semiconductors:
Miscellaneous parts:
User Manual: Prophet tribute site (Lots of good information it appears, some dead links like to the alesis freeloader they claim allows conversion of midi to .wav files...! Is this true?)
Reset Proceedures:
Operating System code:
Patches or knob settings: zicweb patch archive or patch sheets (were on synthfool but I can't find them anymore)
Circuit Overview: below
Scematics/Service Manual: Hylander-pre rev 3 or lazyblueoctopus 3.2/3.3
Common Service Issues/Tips:
Parts Sources: Keys knobs semiconductors misc
Uncommon chips/modules used: rev. 1&2 SSM2030-vco, SSM 2040 vcf, SSM2050 eg, SSM 2020 vca. rev 3-CEM3320 filter, CEM3340 VCO, CEM3310 and both as far as I know use UAF772 dual Bi-Fet op amp, CA3280 dual OTA.
General Info Links: prophet tribute (more exhaustive) Synthesizer Museum (concise rev. history) or Vintage Synth Explorer
Circuit Overview: Being the first fully programmable polysynth the machine had some innovations for its day. The analog signal path does the typical thing of a subtractive using chips as building block chips for VCF, VCO, and EG's. The control is instituted by the D780C NEC processor or on earlier versions the Z80 I'm told. Envelopes are analog creating a richer sound than the later Prophet 600 though it is similar in many other ways. Side by side certain sounds are indicernable which one is creating them. Others, especially with resonance up on filter sweeps, it's quite obvious.
After a recent sale overseas, I had a P5 not output on delivery. Legs vibrated on regulators until they broke. Relieve that stress by bending legs foreward and soldering on flexible wire to the board so that the problem doesn't recur when you see this.
Here's the run down on the problems I experienced with a P5 that supposedly worked ok before setting in the closet:
* After repairing broken regulator legs as above, 5V went down! New Regulator.
* now we had no clock I find. New clock buffer chip 7474 filp flop
* Suddenly...now the battery had also died! I had tested and it was 2.8V! Find that it's running large current due to shorted tantalum filter cap in NV circuit! Replace and digital ok
* Key bushings were mostly shot; replaced all of them and lubed
* INtermittency in area of VCO's..turns out to be power supply feed from the strip at the back of analog board. These white strips have every third pin connect for V+, V-, and ground. Due to boards being stressed they can break pins as some of thes did. Sweep them with 'beep' meter.
* Dirty sockets on CEM3310 EG's were causing a VCA to stay open and intermittent on another.
* One half of a CA3280 was dead on final VCA taking out one voice.
* TL072 half died in S+H for noise source leaving no noise as it went -15V
* A CA3280 totally died which was poly mod vca for two voices.
* Pitch drifting resulting from bad ribbon interconnect. Crimped..ok?
* Cleaned pots..and the pitch wheel needed to be cleaned inside and regreased. Even now if you bump the wheel it still shifts pitch slightly but used with good technique it works ok now. Recommend replacing though if you experience this problem.
Here's a cool tip from J. Haible:
Something I loved about the Prophet (P5 Rev 3.0):
You could plug the CV out (for the lowest note) into the CV in (which would steal one voice from the uC control). That way, you had a "Prophet 4", with 4-VCO bass note and three 2-VCO solo or chord voices. JH.
The knobs are very similar to the ones used on the other SCI synths, except they put this anodized aluminum cap with a pointer cut through the anodization from outer rim to center. techsmechs Of Sweden has remanufactured the typically damaged caps and I have stock of some knobs again if anyone is in need.
D780 and Z80 CPU's- These should be available commonly still from any parts vender. I usually have some.
misc. gate chips- Usually with CD prefix. These are all common and I stock all I think.
LM348 quad op amp- Fairly common. I always stock some of these.
CD4016 analog switch array- Very common. Any parts house. I always stock them.
CA3280 Dual OTA- In production from Intersil it appears.
The Curtiss chips are available where you can get them. Check my stock always here ALso for EARLY rev with SSM2040 they are hard to find, but here is a engineered SSM2040 replacement Module. ALSO The CEM3340 has been reproduced (Contact Cool Audio! ) and rumor Behringer also will make them again. When it rains it pours?
Controls- Rev 1&2 100KB (linear..), Rev. 3 10KB (Also given the design, I don't see why anything between the two would not work on either unit! I haven't tried it though. In a pinch I can't see why even putting in a 5KB for one of them would hurt anything performance or current draw wise.