Yamaha dsp-z7 doa
On Tue, 2 Jun 2020 18:28:17 -0400, M Philbrook
In article ,
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?
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
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
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
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
I've told the owner - no repair / no charge - take it to Yamaha
service - but it hasn't been picked up since.