Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

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Old May 13th 20, 06:48 PM posted to sci.electronics.repair
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Default Yamaha dsp-z7 doa


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

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Old June 6th 20, 09:47 PM posted to sci.electronics.repair
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Default Yamaha dsp-z7 doa

On Tue, 2 Jun 2020 18:28:17 -0400, M Philbrook
wrote:

In article ,
says...

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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