Author Topic: What more i can do?  (Read 37060 times)

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Offline 222Lab_Test222Topic starter

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What more i can do?
« on: October 29, 2024, 07:40:28 am »
Its a 30 years old PCB board and the company stopped making it, so no datasheet and no schematic. It's a hard troubleshooting, the main issues is beeping continuously, after the hard time watching all ICs and stuffs, still couldn't figure out where the problem is.This is a machine controller which is used to dig underground for sewage repair system.

I have lots of those boards with 99% having the error of beep. The beep is continuous beep and no break on between.
I checked all capacitor, no sign of sort, the IC looking good, no burn marks as well as any damages. The SRAM, Flash seems ok as i used that from the working board, MSDOS is good as i used that also from working board. Where am i wrong?

What more to do?
 

Offline 222Lab_Test222Topic starter

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Re: What more i can do?
« Reply #1 on: October 29, 2024, 07:48:25 am »
More Images
 

Offline Harry_22

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Re: What more i can do?
« Reply #2 on: October 29, 2024, 08:04:47 am »
Hi!
If you have 99% of the same faulty boards, it may mean that the external equipment/power supply is also faulty please don't forget it.

But most likely some element has changed its parameters over time. Electrolytes are very suitable for this role, although early caps are less susceptible to "capacitor plague". And you have very few of them there.
The chips are definitely working.

Has the battery finally run out and the BIOS jammed?

PS
Is it possible to connect a monitor to it?
« Last Edit: October 29, 2024, 08:10:58 am by Harry_22 »
 
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Online Sorama

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Re: What more i can do?
« Reply #3 on: October 29, 2024, 08:17:22 am »
the only issue is that it beeps constantly (but works apart from that) , or are there other issues?
 

Offline Phil1977

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Re: What more i can do?
« Reply #4 on: October 29, 2024, 08:57:37 am »
Is there any fan in the system?

Some embedded system mainboards continuously beep if they register some operation parameters are out of tolerance. Values worth to check are
- Fan speed
- Bus voltages
- CPU voltages (AFAIK the Intel 486DX2-66 generally is a 5V-type. But I´d check if there are any 3.3V-parts on the board)
- Battery voltage

 
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Offline Poroit

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Re: What more i can do?
« Reply #5 on: October 29, 2024, 09:01:36 am »
As Harry_22 has posted.

CHECK THE POWER SUPPLY FIRST!
 

Offline PGPG

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Re: What more i can do?
« Reply #6 on: October 29, 2024, 09:30:18 am »
Its a 30 years old PCB board and the company stopped making it, so no datasheet and no schematic.

Just because you don't have a schematic doesn't mean it doesn't exist somewhere. If it's not a problem with one board but with many, then maybe there's a chance of finding it.

As beep is in so many of them I can imagine a situation were something powered by battery (RAM, RTC) need be initiated and beep asks for it. Replacing battery after being died may be not enough, but knowing what is powered by battery may be will allow to find a way to copy contents from working PCB.
 

Offline 222Lab_Test222Topic starter

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Re: What more i can do?
« Reply #7 on: October 29, 2024, 11:06:09 pm »
As Harry_22 has posted.

CHECK THE POWER SUPPLY FIRST!

Power supply is good.
 

Offline 222Lab_Test222Topic starter

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Re: What more i can do?
« Reply #8 on: October 29, 2024, 11:07:26 pm »
Is there any fan in the system?

Some embedded system mainboards continuously beep if they register some operation parameters are out of tolerance. Values worth to check are
- Fan speed
- Bus voltages
- CPU voltages (AFAIK the Intel 486DX2-66 generally is a 5V-type. But I´d check if there are any 3.3V-parts on the board)
- Battery voltage

Yes there is fan which is run by 12V, The voltage regulator is sending 5V to CPU and still searching where 3.3V is going.

One if the IC WE001BF and MSDOS Pins doesnt get require power on Buses.
 

Offline 222Lab_Test222Topic starter

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Re: What more i can do?
« Reply #9 on: October 29, 2024, 11:09:12 pm »
the only issue is that it beeps constantly (but works apart from that) , or are there other issues?
Yes the power supply is good, There is long beep no break, I even change MSDOS as well as RAMs with new working one to check if they are fault BUT still same.
 

Offline 222Lab_Test222Topic starter

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Re: What more i can do?
« Reply #10 on: October 29, 2024, 11:10:37 pm »
Hi!
If you have 99% of the same faulty boards, it may mean that the external equipment/power supply is also faulty please don't forget it.

But most likely some element has changed its parameters over time. Electrolytes are very suitable for this role, although early caps are less susceptible to "capacitor plague". And you have very few of them there.
The chips are definitely working.

Has the battery finally run out and the BIOS jammed?

PS
Is it possible to connect a monitor to it?

Yes, i even changed the CMOS battery with new one.
The capacitor are all good.

Yes there is monitor BUT due to beep there is nothing on monitor, it doesn't even turn on.
 

Online themadhippy

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Re: What more i can do?
« Reply #11 on: October 29, 2024, 11:14:54 pm »
What bios is it using? a single beep can be all's well
 

Offline Manul

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Re: What more i can do?
« Reply #12 on: October 29, 2024, 11:39:34 pm »
My bet would be that RTC or some volatile settings were reset and it detects that.
 

Offline tryingtolearn

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Re: What more i can do?
« Reply #13 on: October 29, 2024, 11:41:06 pm »
Does it beep as soon as pwr is supplied or does it start to beep at a certain point ?
 

Offline 222Lab_Test222Topic starter

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Re: What more i can do?
« Reply #14 on: October 30, 2024, 12:01:24 am »
What bios is it using? a single beep can be all's well

MSDOS 3.21 H AND L
 

Offline 222Lab_Test222Topic starter

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Re: What more i can do?
« Reply #15 on: October 30, 2024, 12:03:19 am »
Its a 30 years old PCB board and the company stopped making it, so no datasheet and no schematic.

Just because you don't have a schematic doesn't mean it doesn't exist somewhere. If it's not a problem with one board but with many, then maybe there's a chance of finding it.

As beep is in so many of them I can imagine a situation were something powered by battery (RAM, RTC) need be initiated and beep asks for it. Replacing battery after being died may be not enough, but knowing what is powered by battery may be will allow to find a way to copy contents from working PCB.

Can you explain a bit more?
 

Offline 222Lab_Test222Topic starter

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Re: What more i can do?
« Reply #16 on: October 30, 2024, 12:04:22 am »
My bet would be that RTC or some volatile settings were reset and it detects that.

Can you explain a bit more?
 

Offline 222Lab_Test222Topic starter

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Re: What more i can do?
« Reply #17 on: October 30, 2024, 12:06:09 am »
Does it beep as soon as pwr is supplied or does it start to beep at a certain point ?

power given it start to beep, nothing on display.
 

Offline tryingtolearn

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Re: What more i can do?
« Reply #18 on: October 30, 2024, 12:29:16 am »
So this statement would lead me to look at other components in the set up.
"I have lots of those boards with 99% having the error of beep"
how many are you talking?  the one percent that didnt - may have another issue
but doubtful 99% of all tested have the same error to give you a steady tone upon power.

Was the same blank monitor used for all boards tested? 
Any other shared components used when swapping boards for testing?
 

Offline 222Lab_Test222Topic starter

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Re: What more i can do?
« Reply #19 on: October 30, 2024, 12:34:50 am »
All the boards have same issues, Normally on other board when that long beep occurs either its the CMOS battery is dead, or RAM or bios is dead.
If i change that things, maximum times those beep is gone and boards is working normal.

But now in few more boards, the same isssues BUT even if i change those with new working ones, they are not running and beeping continuos, I havent touch the ICs yet, and there is no burn or damage mark anywhere, the capacitor looking good, no bulky ones and damages ones.

I have tested on two monitor which is working fine with another motherboard.
 

Offline PGPG

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Re: What more i can do?
« Reply #20 on: October 30, 2024, 01:07:19 am »
Can you explain a bit more?

Your following sentence looks to deny what I was thinking about:

when that long beep occurs either its the CMOS battery is dead ...
If i change that things, maximum times those beep is gone and boards is working normal.

I just supposed that there are some crc in configuration in RAM in RTC IC or the time that is after its reset (1970 ?) not accepted, but as replacing dead battery helps probably it is not this.

From what you write now it looks that it starts from testing everything and any error = beep.
I would expect error number somewhere. Once upon a time we send just after power on the device information through its normal LED and used foto-detector connected to COM port to read it.
 

Offline 222Lab_Test222Topic starter

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Re: What more i can do?
« Reply #21 on: October 30, 2024, 01:29:06 am »
Can you explain a bit more?

Your following sentence looks to deny what I was thinking about:

when that long beep occurs either its the CMOS battery is dead ...
If i change that things, maximum times those beep is gone and boards is working normal.

I just supposed that there are some crc in configuration in RAM in RTC IC or the time that is after its reset (1970 ?) not accepted, but as replacing dead battery helps probably it is not this.

From what you write now it looks that it starts from testing everything and any error = beep.
I would expect error number somewhere. Once upon a time we send just after power on the device information through its normal LED and used foto-detector connected to COM port to read it.

After couple of weeks test here and there, i somehow find that those MSDOS are not getting input address bus voltages.
A16 and A17
 

Offline Harry_22

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Re: What more i can do?
« Reply #22 on: October 30, 2024, 06:07:54 am »
All the boards have same issues, Normally on other board when that long beep occurs either its the CMOS battery is dead, or RAM or bios is dead.
If i change that things, maximum times those beep is gone and boards is working normal.
Seems the answer is here.
What do you mean under "bios is dead"?


After couple of weeks test here and there, i somehow find that those MSDOS are not getting input address bus voltages.
A16 and A17

The chip type (UV EEPROM size) is set in the Bios?
Take out them on working board and check it for beep (Check the working board without chips).
« Last Edit: October 30, 2024, 06:22:48 am by Harry_22 »
 

Online radiolistener

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Re: What more i can do?
« Reply #23 on: October 30, 2024, 06:18:00 am »
since it is very old, it is possible that ROM chips are loss their information, so the beep may be a signal that ROM checksum is failed
 
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Offline 222Lab_Test222Topic starter

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Re: What more i can do?
« Reply #24 on: October 30, 2024, 06:41:13 am »
All the boards have same issues, Normally on other board when that long beep occurs either its the CMOS battery is dead, or RAM or bios is dead.
If i change that things, maximum times those beep is gone and boards is working normal.
Seems the answer is here.
What do you mean under "bios is dead"?


After couple of weeks test here and there, i somehow find that those MSDOS are not getting input address bus voltages.
A16 and A17

The chip type (UV EEPROM size) is set in the Bios?
Take out them on working board and check it for beep (Check the working board without chips).

yes there is beep if those EPROM is removed from working board.
I think thats the BIOS.
 


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