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Lift CPU board

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2PAC Mafia

Member
Hi,

I have to repair some CPU lift boards. I have tested all the simple digital IC´s and passive components and all are OK. Measuring consumption and touching (heat) some other complex IC´s I thing I have problems. I would like to replace all of them to be sure I´m solving the problem but my question is about these IC´s. They are:

8255A (Programmable Peripheral Interface)
8254 (Programmable Interval Timer)
8085AH-2 (Single chip 8 bit N channel microprocessor)
8259A (Programmable Interrupt Controller)

Apart of these I have 2 EEPROM 27256 and 2 static RAM. Could I replace these list of components? are they programmed through the software stored at EEPROMs?
 

ClydeCrashKop

Well-Known Member
Most Helpful Member
The 8255 chips are prone to have individual output pins go bad.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Apart of these I have 2 EEPROM 27256 and 2 static RAM. Could I replace these list of components? are they programmed through the software stored at EEPROMs?
They will be EPROM (not EEPROM), it's very likely that the 27256's contain the entirely programming for the microprocessor, so couldn't be replaced (unless you could source ones ready programmed by the original manufacturer of the board).

However, you don't repair items by testing components, you need to test the entire design as a whole and fault find from there.
 

2PAC Mafia

Member
They will be EPROM (not EEPROM), it's very likely that the 27256's contain the entirely programming for the microprocessor, so couldn't be replaced (unless you could source ones ready programmed by the original manufacturer of the board).

However, you don't repair items by testing components, you need to test the entire design as a whole and fault find from there.
What I want to replace are not the EPROM, are these components (in case that are programmed by the EPROM):

8255A (Programmable Peripheral Interface)
8254 (Programmable Interval Timer)
8085AH-2 (Single chip 8 bit N channel microprocessor)
8259A (Programmable Interrupt Controller)

I only have this board, I don´t have the complete system so my only way to repair it is testing components in this case. I can´t get the lift with me in my workshop... :)

We know the problem is at this board by replacing it.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
What I want to replace are not the EPROM, are these components (in case that are programmed by the EPROM):

8255A (Programmable Peripheral Interface)
8254 (Programmable Interval Timer)
8085AH-2 (Single chip 8 bit N channel microprocessor)
8259A (Programmable Interrupt Controller)

I only have this board, I don´t have the complete system so my only way to repair it is testing components in this case. I can´t get the lift with me in my workshop... :)
Even without the lift, you should be able to do a considerable amount of testing on it - obviously first thing though, the actual 'fault' should give you a major clue to the problem.

You don't mention anything about the symptoms?, but assuming it's dead? then common causes are PSU issues, clock issues, and reset issues - IC failures in uP systems are pretty uncommon.
 

spec

Well-Known Member
Most Helpful Member
Hi,

I have to repair some CPU lift boards. I have tested all the simple digital IC´s and passive components and all are OK. Measuring consumption and touching (heat) some other complex IC´s I thing I have problems. I would like to replace all of them to be sure I´m solving the problem but my question is about these IC´s. They are:

8255A (Programmable Peripheral Interface)
8254 (Programmable Interval Timer)
8085AH-2 (Single chip 8 bit N channel microprocessor)
8259A (Programmable Interrupt Controller)

Apart of these I have 2 EEPROM 27256 and 2 static RAM. Could I replace these list of components? are they programmed through the software stored at EEPROMs?
Hi 2PakMafia,

Yes, you can replace all the the chips. None of them store any information, including code.

spec
 

2PAC Mafia

Member
Hi 2PakMafia,

Yes, you can replace all the the chips. None of them store any information, including code.

spec
Thanks a lot, this was my question because as I said the rest of things I already tested.

No power supply dedicated circuit, 5v coming in from another board.
 

spec

Well-Known Member
Most Helpful Member
No probs 2PAK Mafia,

The 8085 brings back memories of the heady days of pioneering personal computers.

And Palma brings back memories of many enjoyable holidays in Majorca.:cool:
The last time I was in Palma, my wife and I took the railway to the north.:happy:

spec
 
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2PAC Mafia

Member
Good, so you know our special and beauty island!!! Best regards.
 

dr pepper

Well-Known Member
Most Helpful Member
You could measure the current draw of the circuit and then using the datasheets estimate what it should be, if something is overheating draw is probably excessive.
You could do this on the bench.
 

2PAC Mafia

Member
Yes, I was thinking about that too but even like this it makes me doubt about if they are 100% so I will replace them.

My IC tester can test some of them but it needs a special adapter which I don't have.

When the lift technicians test the boards they have to go to hotels because this system is very old, I think it's already obsolete from Orona, so I prefer to avoid doubts and have a high % they are repaired.
 

dr pepper

Well-Known Member
Most Helpful Member
There is a lift not far from here if it hasnt been replaced yet that uses mercury arc rectifiers like my avatar.
 
Last edited:

ChrisP58

Well-Known Member
Another possible failure source is age. Programmed parts don't have infinite memories. It varies by different technologies and processes, but your EPROM might only have a lifetime endurance spec of 10 or 20 years. Based on the vintage of the processor used, your assembly is probably at least 30 years old.

So it may be that the data in the EPROM has just become corrupted. Even a one bit change can cause a problem in what it's supposed to do, or cause a CRC check to fail so the processor abort operation.
 

spec

Well-Known Member
Most Helpful Member
Another test you can make is to check that the supply voltages on all the chips are correct (meaure directly on the chip pins, 0V and Vcc).

spec
 

2PAC Mafia

Member
Hi,

Another possible failure source is age. Programmed parts don't have infinite memories. It varies by different technologies and processes, but your EPROM might only have a lifetime endurance spec of 10 or 20 years. Based on the vintage of the processor used, your assembly is probably at least 30 years old.

So it may be that the data in the EPROM has just become corrupted. Even a one bit change can cause a problem in what it's supposed to do, or cause a CRC check to fail so the processor abort operation.
They supplied me the board without EPROM because they used the EPROM at spare working board.

Another test you can make is to check that the supply voltages on all the chips are correct (meaure directly on the chip pins, 0V and Vcc).

spec
OK, thanks.
 
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