The ac line relay cycles for 500mS, without display indications. This with or without main TX connected. Housekeeper is live and rises to 13V during the start-up attempt. Power detect line ok.
Anyone familiar with start-up sequence of this thing?
Looks like you've got to disassemble the whole thing to get at the processor/control area.
Is it safe to bypass relay, to run up the power gradually?
RL
I have no idea basically what you are talking about except maybe a power management circuit that isn't getting a watch dog trigger from the CPU ?
Normally those kinds of circuits requie some sort of feed back information to keep it alive...
I Suppose the proper thing to do is watch that feed back information to see if this is the case.
In some cases it could be a rather high speed pulse coming from a Digital timer or CPU. when that stops the circuit will time out and shut down..
I assume this is what you are referring to ?
Even with a full schematic, the requirements for the main processor to keep the line relay closed and running is not obvious.
Two of these cycles from O/I switch latches the unit off until line input power itself is cycled.(There is a dual flipflop in the housekeeping circuitry).
All supply lines are monitored to develop 'power good', but there's no obvious power circuit failure evident during the period of relay closure - except that the front panel doesn't even blink.
All service troubleshooting involves interaction with the front panel display. . . .with specialized harness extenders and board substitutions.
The harnessing is nuts, with signals routed through 4 or 5 cards and connectors before arriving at their destination. I expect the organization of power circuits and control logic will be similarly convoluted.
I've told the owner - no repair / no charge - take it to Yamaha service - but it hasn't been picked up since.
RL
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