Sequential prophet 5 - Led Matrix.5-2; Computer.5-2; Non-Volatile Procram Memory.5-3

5-4 LED MATRIX
If the Prophet powers-up with a few bright LEDs, but doesn't operate, you can assume the computer isn't
running.
Some owners may notice a slight difference in brightness between the BANK and PROGRAM numerical
displays. This is normal, resulting from different scan times for each display.
If a switch LED doesn’t indicate switch status (on or off), check that the switch is indeed functioning. For
example, if S213 enables OSC B PULSE but DS213 doesn't light, check operation of LEDs connected in the
same matrix row or column: DS203 10. DS105. and the c-segments of DS225. If they didn t work, the
problem might be R219, Q201, R240. or U2Q8.
Check for CS8 and CS9.
5-5 COMPUTER
See also paragraph 5-6.
Most computer malfunctions are caused by failures of devices connected to the data bus(W a «-
forms 5-OA and B show a normal bus line.) For example, any shorted latch mput may prevent that
entire data line from ever being a 1. Shorts between data lines will confuse the computer ternWy.
If you suspect a data bus problem, try to pick out the lines with questionable level*, Ltw. *ouW
be 0-500mV. High should be 4-5V (3.5V for CMOS). Reading of lor 1JV for example !"?..! X
failure. First, check *12V and -5V supplies. Then remove any wcketecHoomputw) *"<*.1-1322
clock. U312/13 EPROMs, or the appropriate 6508 - WHICH WILL CLEAR
If this doesn't locate the problem, you will have to cut traces to aH other data-bus^d ^vk« u~U
correct levels are restored. Note that a short on the high voltage data-bus. DBH. will not usually affect
computer operation. But it will be easy to check each latch for malfunctioning swttch (S) bus. CATE
bits, or S/H addresses.
CSO is the earliest CS. so maybe used for "loop sync".
If the computer "dies" seemingly randomly, you might check U322 CPU CLOCK for intermittents.
Also check that 1710 and P301 are firmly interlocked. If the computer doesn t come up at all, the
problem could be a tuning problem. Pull W703 and try again. If the panel now lights normally (after
5-7 seconds) check either OSC 1A — which can hang up the TUNE routine, if dead or U301 -08.
If computer TUNEs too quickly, or not at all, check U316. Bad 6508s may also cause erratic tunings,
since they hold the BIAS values.
V6 NON-VOLATILE PROGRAM MEMORY
NOTE: The NV PRGM RAM is well-protected, but not foolproof. Technicians should warn players
that their programs can be lost through the course of repair, and encourage them to back-up their
patches with diagrams. Panel blanks are available from the factory.
CAUTION: Any Vdd short will clear the program memory.
If programs will not record, check BT301, Vdd, and whether -CS, U309-1 remains high throughout
power-up or down. The briefest pulse here may erase a few bytes.
C389 should be able to hold Vdd for a few minutes - but we don’t guarantee it. This may allow you
time to insert a microammeter in series with BT301. Total current draw should be about 10 M A or less.
A single, bad 6508 can draw as much as 50 nA.
WARNING: BT301 may explode if shorted for any period of time — though it will usually "just
vent noxious gases.