Electronics > Repair
What more i can do?
fzabkar:
The scope traces suggest that the beeping stops as soon as Reset is released. This in turn suggests that this is happening well before BIOS starts executing. However, the OP has reported that the beeping continues on a good motherboard if the EPROMs are not present. This would suggest that BIOS code is switching off the beeping. I don't get it. :-?
Harry_22:
--- Quote from: fzabkar on November 19, 2024, 09:54:55 pm ---The scope traces suggest that the beeping stops as soon as Reset is released. This in turn suggests that this is happening well before BIOS starts executing. However, the OP has reported that the beeping continues on a good motherboard if the EPROMs are not present. This would suggest that BIOS code is switching off the beeping. I don't get it. :-?
--- End quote ---
Yes, you are right. Something looks strange.
@222Lab_Test222, could you take out both EPROMS from working board and track the beep signal as usual. Reduce the time/div to detailed view the delay between reset release and beep stop. First with EPROMs and next without.
fzabkar:
--- Quote from: Harry_22 on November 19, 2024, 10:07:15 pm ---@222Lab_Test222, could you take out both EPROMS from working board and track the beep signal as usual.
--- End quote ---
I wonder if it might be an idea to scope the OE and CE pins of the EPROMs? The OP has reported that there is activity on all the address lines other than the high order A16 and A17. I'm wondering whether the pre-BIOS beeping is non-fatal and still allows the BIOS to POST, at least until it encounters a problem?
This is how I imagine the two EPROM layouts (the high order address space is occupied by MS-DOS):
--- Code: ---256K .--------. A17 .--------. 0x3FFFF
| | | |
| | | |
| | | |
| MS-DOS | | MS-DOS |
| | | |
| v3.21 | | v3.21 |
| | | |
| | A16 | | 0x10000
64K |--------| |--------|
| | A15 | | 0xFFFF
| BIOS | | BIOS |
| | | |
|KDX 1.34| |KDX 1.34|
0K '--------' A0 '--------' 0x0000
High byte Low byte
D15 - 8 D7 - 0
--- End code ---
222Lab_Test222:
Reset#
IC1 reset signal is connected to IC2 Pin 1, IC5 Pin 1, IC23 Pin 6, TORNADO IC Pin 77.
CLK, including 66 MHz quartz and logic around it.
It is connected to IC6 Pin 3, IC7 Pin 2
Track pin3 MB3771 (Power Good?) and pin2 (Gnd or not)
Pin 3 doesnt have any power, Pin 2 is not GND, there is some voltage, it is connected to Resistance and then VCC.
222Lab_Test222:
There are some more ICs under BIOS MSDOS, You guys noticed or not?
IC5 74LS07
IC17 74F32
IC71 74HC125A
Green LED is connected to IC5 via resistance.R26
Red LED is connected to IC5 via resistance.R6
Buzzer is connected to SWITCH SW4, the 4th pin is used to toggle sound on or off. Then it is on IC21 Pin 2, and that is near Tornado IC.
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