Troubleshooting Microcontroller Resets for Car Radio Repair

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The discussion focuses on troubleshooting a Grundig beta 5 car radio experiencing resets when the power button is pressed, with jumbled display segments appearing before shutdown. The microcontroller OE57S was identified, and the reset pin was located, revealing a 5V-0V-5V signal indicating the controller is being reset at power-on. However, issues persist with the collector of transistor CT2061, which fails to drop low, suggesting a potential problem with the voltage regulator CIC2051 or a heavy load causing it to shut down. Participants recommend inspecting the filter capacitors for leakage or deformation as they may be contributing to the issue. The discussion emphasizes the importance of analyzing the signals related to the reset and power management circuitry for further diagnosis.
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Hi all,

Trying to fix a car radio (Grundig beta 5) for a local lad who wants it for his car. When you press the soft power button, some jumbled segments appear on the display, then it shuts down.

I'm wondering if the microcontroller is not getting a reset signal. It's labelled OE57S. How do I find the reset pin to check this?

Also, any other troubleshooting tips would be very helpful!

Many thanks
 
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Google ' MC68HC11KA4-SMART- GRUNDIG- OE57S '
 
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Nidum said:
Google ' MC68HC11KA4-SMART- GRUNDIG- OE57S '
I have done so - lots of pages in Polish, for some reason - but no pinout.
 
Try looking for data on the basic module : MC68HC11 .
 
Nidum said:
Try looking for data on the basic module : MC68HC11 .
Thanks - that revealed some pinouts, but not the right one.

Written on the chip is:
[Motorola symbol]
VW BETA 5
BY GRUNDIG
OE57S
QQFG9815

It's a 68-pin package.
 
You probably saw this one : http://www.nxp.com/assets/documents/data/en/data-sheets/M68HC11E.pdf

The only other thing that I can think of is to try searching on 'Grundig car radio data sheets '
 
Thanks to you both, I found the reset pin (58) and, with a bit of fiddling, caught a 5V-0V-5V 'blip' on my CRO as I pressed the power button.

Seems like the controller is being reset at power on.

Where would you go from here?
 
IMG_0362.PNG

Further to this, I'm no longer sure the reset is working. In the above schematic, transistor CT2061's base and emitter start low, then pulse high on pressing the power button, indicating a healthy reset input signal. However, the collector does not - it starts high, maybe 'blips' slightly on power-on, but never fully drops low. I've replaced it to no avail. Why might this be happening?
 
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Guineafowl said:
Why might this be happening?
Because CIC2051 is a voltage regulator with +5V output on pin 8. Both it and CT2061 appear to be operating normally.

On the schematic, signal "+G" is shown as having 5V on it, presumably this is during normal operation or there would be a note or waveform shown.
Since "+G" is only a pulse and it is controlled by by signal "+S", find out why "+S" is a pulse and not a level.

The "-RESET" signal is generated on CIC2051 pin 7. It is the inversion of CIC2051 input pin2.

Edit[/color] Since CIC2051 regulator has overcurrent protection built into it, there could be a heavy load causing it to shut down. Prime suspects for a heavy load are the filter capacitors on the "+G" line. Visually inspect the electrolytic capacitors for leakage (white residue near the leads) or a deformed case (bulging top on upright capacitors.)end Edit[/color]
 
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  • #11
CT2061 is for switching a 5V rail (+G) on and off. If you are seeing a glitch on the collector then everything goes dead that seems to indicate a short on the switched rail.

BoB
 
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