Electronics > Repair
What more i can do?
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222Lab_Test222:

--- Quote from: Sorama on November 19, 2024, 07:33:03 am ---
If you know (electrically) what drives the beeper and in the end which transistor/ processor pin, it may help you understand the prerequisites/conditions for the beeper and thus why it is beeper. Just follow the signal of the beeper.

--- End quote ---
So i should track the beeper pin to where they are connected you mean?
Harry_22:

--- Quote from: 222Lab_Test222 on November 19, 2024, 07:30:28 am ---
--- Quote from: Harry_22 on November 19, 2024, 06:33:21 am ---Just raise 11 pin as I wrote but literally by half a millimeter.


--- End quote ---
Here it is,
The Pin is raised
The second image is the signal of TP1 non working board after RTC TP raised...

--- End quote ---

So we have got the same High level signal on Pin 11 RTC.
No reaction? The same continuous beep? Seems so.

@fzabkar, we tried to get High level as on working board. Now we got it. Nothing has changed.
The timer does not cause a malfunction, although I wanted to believe it so much.


That's it, we forgot about RTC.
Harry_22:
It seems you said that the beeper is connected to the Tornado-T chipset.
As we can see from the picture, the beeper signal is generated immediately upon power supply.
When Reset is released it disappears.
In our case either the Reset signal does not reach the chipset or it is held, for example, by the video card, ISA bus. Or there is another signal in the system, some Hardware Ready.

1. Ring that the Reset signal reaches the chipset. Remember the pin.
Make a broom out of a stranded wire (see the picture). You will find the connections in the board much faster (especially on boards with many small SMD parts).
2. Check the signal on OSC3 quartz near the chipset.
3. Measure and compare traces from both LEDs on both machines.
fzabkar:
FWIW, this is the speaker section from the original IBM PC-AT Tech Ref Manual:

https://web.archive.org/web/20230522144349/http://www.users.on.net/~fzabkar/PC-AT/TimerCounter.jpg

https://web.archive.org/web/20230522144349/http://www.users.on.net/~fzabkar/PC-AT/at-16of22.JPG

https://web.archive.org/web/20230522144349/http://www.users.on.net/~fzabkar/PC-AT/at-17of22.JPG

The speaker data is on bit #1 of port 61h. It is set to 1 after a system reset.

https://bitsavers.org/pdf/ibm/pc/at/1502494_PC_AT_Technical_Reference_Mar84.pdf

https://bitsavers.org/pdf/ibm/pc/at/
Harry_22:
WACOM Tornado-T chipset should be similar with other 80486 Green PC ISA-VESA Systems.

The task is for you to trace the main signals along the path of the processor, chipset, and small logic.

Reset#
CLK, including 66 MHz quartz and logic around it.
Track pin3 MB3771 (Power Good?) and pin2 (Gnd or not)
Try to find 14 MHz clock signal.

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