What more i can do? - Page 1
Forum section: electronics / repair

author: 222Lab_Test222
author_rank: Frequent Contributor
timestamp: October 29, 2024, 07:40:28 am
content: 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?

author: 222Lab_Test222
author_rank: Frequent Contributor
timestamp: October 29, 2024, 07:48:25 am
content: More Images

author: Harry_22
author_rank: Frequent Contributor
timestamp: October 29, 2024, 08:04:47 am
content: 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?PSIs it possible to connect a monitor to it?

author: Sorama
author_rank: Frequent Contributor
timestamp: October 29, 2024, 08:17:22 am
content: the only issue is that it beeps constantly (but works apart from that) , or are there other issues?

author: Phil1977
author_rank: Frequent Contributor
timestamp: October 29, 2024, 08:57:37 am
content: 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

author: Poroit
author_rank: Frequent Contributor
timestamp: October 29, 2024, 09:01:36 am
content: As Harry_22 has posted.CHECK THE POWER SUPPLY FIRST!

author: PGPG
author_rank: Frequent Contributor
timestamp: October 29, 2024, 09:30:18 am
content: Quote from: 222Lab_Test222 on October 29, 2024, 07:40:28 amJust 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.

author: 222Lab_Test222
author_rank: Frequent Contributor
timestamp: October 29, 2024, 11:06:09 pm
content: Quote from: Poroit on October 29, 2024, 09:01:36 amPower supply is good.

author: 222Lab_Test222
author_rank: Frequent Contributor
timestamp: October 29, 2024, 11:07:26 pm
content: Quote from: Phil1977 on October 29, 2024, 08:57:37 amYes 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.

author: 222Lab_Test222
author_rank: Frequent Contributor
timestamp: October 29, 2024, 11:09:12 pm
content: Quote from: Sorama on October 29, 2024, 08:17:22 amYes 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.

author: 222Lab_Test222
author_rank: Frequent Contributor
timestamp: October 29, 2024, 11:10:37 pm
content: Quote from: Harry_22 on October 29, 2024, 08:04:47 amYes, 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.

author: themadhippy
author_rank: Super Contributor
timestamp: October 29, 2024, 11:14:54 pm
content: What bios is it using? a single beep can be all's well

author: Manul
author_rank: Super Contributor
timestamp: October 29, 2024, 11:39:34 pm
content: My bet would be that RTC or some volatile settings were reset and it detects that.

author: tryingtolearn
author_rank: Contributor
timestamp: October 29, 2024, 11:41:06 pm
content: Does it beep as soon as pwr is supplied or does it start to beep at a certain point ?

author: 222Lab_Test222
author_rank: Frequent Contributor
timestamp: October 30, 2024, 12:01:24 am
content: Quote from: themadhippy on October 29, 2024, 11:14:54 pmMSDOS 3.21 H AND L

author: 222Lab_Test222
author_rank: Frequent Contributor
timestamp: October 30, 2024, 12:03:19 am
content: Quote from: PGPG on October 29, 2024, 09:30:18 amCan you explain a bit more?

author: 222Lab_Test222
author_rank: Frequent Contributor
timestamp: October 30, 2024, 12:04:22 am
content: Quote from: Manul on October 29, 2024, 11:39:34 pmCan you explain a bit more?

author: 222Lab_Test222
author_rank: Frequent Contributor
timestamp: October 30, 2024, 12:06:09 am
content: Quote from: tryingtolearn on October 29, 2024, 11:41:06 pmpower given it start to beep, nothing on display.

author: tryingtolearn
author_rank: Contributor
timestamp: October 30, 2024, 12:29:16 am
content: 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 issuebut 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?

author: 222Lab_Test222
author_rank: Frequent Contributor
timestamp: October 30, 2024, 12:34:50 am
content: 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.

author: PGPG
author_rank: Frequent Contributor
timestamp: October 30, 2024, 01:07:19 am
content: Quote from: 222Lab_Test222 on October 30, 2024, 12:03:19 amYour following sentence looks to deny what I was thinking about:Quote from: 222Lab_Test222 on October 30, 2024, 12:34:50 amI 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.

author: 222Lab_Test222
author_rank: Frequent Contributor
timestamp: October 30, 2024, 01:29:06 am
content: Quote from: PGPG on October 30, 2024, 01:07:19 amAfter couple of weeks test here and there, i somehow find that those MSDOS are not getting input address bus voltages.A16 and A17

author: Harry_22
author_rank: Frequent Contributor
timestamp: October 30, 2024, 06:07:54 am
content: Quote from: 222Lab_Test222 on October 30, 2024, 12:34:50 amSeems the answer is here.What do you mean under "bios is dead"?Quote from: 222Lab_Test222 on October 30, 2024, 01:29:06 amThe 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).

author: radiolistener
author_rank: Super Contributor
timestamp: October 30, 2024, 06:18:00 am
content: 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

author: 222Lab_Test222
author_rank: Frequent Contributor
timestamp: October 30, 2024, 06:41:13 am
content: Quote from: Harry_22 on October 30, 2024, 06:07:54 amyes there is beep if those EPROM is removed from working board.I think thats the BIOS.