Just finished repairing a DP4 (classic) Rev C (1992).
DP4 is the older version, all thru-hole -- as opposed to SMD in the DP4+. All audio ICs on the DP4 classic seem to be TL07XCP type, but I didn't check too thoroughly. Sill looking for schematics, although the unit is up and running again.
I had picked the unit up cos it was described as not fully working, for repair or replacement parts. When I turned it on to play around and dial in some algorithms, it failed within 10 minutes -- all lights off.
- 7915 voltage shorted to ground
- 2 x blown fuses (feeding 15V regs)
- 1 x 7905 replaced cos probably blown, (measured weird on diode tester)
- 1 x 220n cap near power regulator definitely shorted internally (it sits very close to a heat sink)
Also replaced ALL elcos (I used axial, bent and placed flat, all rated for 105 degrees) and replaced several 220n caps near power regulator heat areas (caps bent away from heat sink). Finally, sub'ed tantalum caps (22/20V and 10/15V) for electrolytics.
The heat sinks in the middle of the board get too hot to touch (same with DP4+). But here the heat sinks are larger.
The heat sink on the right side, screwed to the case, gets pretty hot too.
Unit requires sufficient ventilation on the side when racked, as the case itself gets warm.
Program encoder knob was missing. Replaced. Encoder shaft is 6.4mm.