Electronics > RF, Microwave, Ham Radio

Icom IC-736 front panel problem

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mehdi:
Today I came across an Icom IC-736 which seemed very very new (the seller claimed it wasn't used and I think he was right)
I turned it on. It turns on, the LCD has backlight, but is empty (no text is shown on the display) and a white noise can be heard from the speaker; S-meter also is on its maximum value (right-most). The panel buttons don't work.
I checked these things with no success:

* Reset the CPU (holding Ent and CLEAR and turning on the device)
* Took the lithium battery out
* Checked the power supply voltage at some test points and they were OK
* Checked the voltage of some logic board ICs and they were 5VR20 (47 ohm) on control panel unit seemed to have problems (had changed color a bit) but it was OK (the 7805 besides it was also OK)

Any ideas what could be wrong, or how can I pinpoint the problem?

Thanks in advance

TheSteve:
If all test voltages from the service manual are fine then I would carefully re-seat all of the various board interconnects. If that doesn't make a difference then we'll dig into the service manual further.

Radio Tech:
I would check those connectors as TheSteve requested.
Also remember this radio has a built in power supply. And it is a switch mode unit.  Check the rails for correct voltage and ripple.

mehdi:
Thanks.
All the voltages are OK; The CPU does not send any control commands to the LCD driver;
I think one of these could be the reason:
1- The CPU may have been damaged.
2- The EPROM contents may be corrupted.

What do you think? (We have another IC-736, so we can copy the contents of EPROM and program the faulty one with it)

GandalfDerGraue:
any signals on the CPU to be seen with an oscilloscope? If not, is there kind of reset logic nearby the CPU, some capacitor being pulled up or down by some resistor going directly to an CPU Pin? Often there are problems with dried electrolytic caps.

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