Electronics > Repair
What more i can do?
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Poroit:
G'day All,

222Lab_Test222,Harry_22, fzabkar you are all doing a great job trying to fault find this PCB. Please keep it up :-+

You other Guys need to reread the Forum Rules.

"Regulars, please be extra nice to beginners asking questions. Do not deride them for anything, if you can't be nice, don't post.""

Att: PA0PBZ.....suggest who he could send them to!



Harry_22:
Hello Collegues!


222Lab_Test222, would you see what happens when the machine starts:

1. The Reset# signal is removed.
This occurs 200ms after the supply voltage and clock signals are established.

2. The processor begins initialization and loading the BIOS program.
"The Intel486 OX microprocessor will start executing instructions at location FFFFFFFOH after RESET.
When the first InterSegment Jump or Call is executed, address lines A20-A31 will drop LOW for CS-relative memory cycles, and the Intel486 OX microprocessor will only execute instructions in the lower
one Mbyte of physical memory. This allows the system designer to use a ROM at the top of physical memory to initialize the system and take care of RESETs." (Page 6-11 of Intel486_DX2_Microprocessor_Data_Book_Jul92.pdf)

3. We have already traced the interaction of the processor with EPROM with the BIOS.
It goes like this. The processor sets the address and activates the Chip Enable#.
The Output Enable# clock reads data from the EPROM.
Then the address changes and the data is read again by OE#.

4. On the good machine you can see that after 20 microseconds CE# disappears and one more signal appears on the data bus from another device on the bus.

5. On a non-working machine, a fatal error occurs immediately after the seventh cycle if viewed on the D0 bus.
It should be noted that in a time period less than 3 μs from Reset# release , the processor initializes internal registers.

I missed one thing. You wrote:"Another another things i am worried is the blink of Green LED. WHY?
--In non working board, it blinks sometimes and it doesn't blink sometimes. Does it affect?"

This is very important. This is a result of unstable operation. The non-working machine loading every time has different breakpoint


Here, when diagnosing such a fault, we must remember that several boards have similar symptoms.
It follows that it could be a component like a capacitor that loses capacity over time. There may be a broken contact in the DIP switch. There may also be jamming of the CMOS memory due to low battery.
Knowing what reliable equipment was assembled in Japan at that time, I do not believe that this could be a chip malfunction.
Well, maybe specifically one with a built-in defect.
We have already looked at all possible options and now we are just looking at step-by-step loading. I am sure that we must find the problem. Even if you have to write down all the addresses and data and compare them with the contents of the EPROM.

222Lab_Test222, please make a manual reset button and view all the data and address signals on a non-working machine. We look for any deviation in amplitude, rise and fall fronts. If you have any doubts, print screenshots here and we’ll figure it out together.

PS
Yes, there are many more professionals here who can also express their assumptions.
Welcome everyone!
222Lab_Test222:
Manual reset button, whats that and how can i made it?
Poroit:
G'day All,

Att: Harry _22.

I see your last post suggests the issue could be caused by:

1.Capacitor that loses capacity over time.
 
2.Broken contact in the DIP Switch.

3.Jamming of the CMOS memory due to low battery.

Att:222Lab_Test222

I suggest you change out all the caps and battery on one of the faulty boards so that they can be crossed off the list.

BTW.
I assume this Controller is linked to a Hydraulic Package that is used to steer the cutting head.

Can you send some pics of the Interface between the Controller and the Hydraulic package.

Thinking ahead...if this fault is due to a component that can no longer be sourced, you may be keen to build a new Controller using Raspberry Pi.








Harry_22:
I also encountered an atypical malfunction in old equipment from Rohde&Schwarz (Aviation transceivers). SMD resistors of certain values ​​break. There have already been several cases.
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