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SH7034 processor in Roland XP-80 synth won't boot. Help please!

Discussion in 'General Electronics Discussion' started by Vido, Sep 28, 2019.

  1. Vido

    Vido

    1
    0
    Sep 27, 2019
    Hello all,

    The detoriation of the electrolytic capacitors is a known problem of the Roland XP-80 synthesizer. I have one, love it, and it started to get problems too. So I replaced all electrolytic caps in two shifts.
    First all the audio-related caps. After this my XP80 sounded wonderful again.
    In the second shift I replaced all remaining electrolytic capacitors of the main board. And now the XP80 won't boot anymore...

    When switching a working unit on, the display goes on, kind of flickers and an animated logo of XP80 comes up, after which the buttons light up and the sound engine starts.
    In my unit only the screen is illuminated, flickers and then freezes.
    Sometimes a number of buttons light up and go out again. In seemingly random patterns. The synth does not react to button presses.
    I can provoke the same long button-light pattern when trying to boot the synth in test mode (by keeping the EFX-Utility and Rhythm buttons pressed for 10s during switch-on.

    I checked all cap connections with neighboring components. They are all okay. I checked the voltages and ground connections. All is okay. I doublechecked the polarity and value of the mounted caps. All are okay.

    I did not yet replace the large electrolytic caps of the power board. (I plan to do so).

    The problem lies probably in the CPU IC. It is IC12 on the main board. It is a Hitachi (nowadays Renesas) SH7034 family processor. I downloaded the bulky manual of this processor, but I cannot find any handles about the booting process.
    All Vcc (+5V) and Vss (ground) connections on the corresponding pins are okay (a prerequisite for starting the chip). A manual reset works, but restores the same freezing state.
    Can anyone shed some light on this processor what to do or what to test to get this processor going?
    Can it be a timing problem of some sorts?

    Here are links to the
    * XP-80 service manual: https://www.scribd.com/document/48697252/XP80-service
    * SH7034 manual: https://www.rockbox.org/wiki/pub/Main/DataSheets/sh7032h.pdf

    Any help is greatly appreciated!!
     
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