Hi all,

I have a couple of circuit boards, one working one not!
They're pretty old and both have a 27c256dc-12 processer on them.

I know very little about these at the moment, I'd like to make a duplicate of the one on the working board to rule that out as a problem.

RS list a copier, would that be the way to go? Is there code protection on these chips?

Cheers Geoff

 

Hi all,

I have a couple of circuit boards, one working one not!
They're pretty old and both have a 27c256dc-12 processer on them.

I know very little about these at the moment, I'd like to make a duplicate of the one on the working board to rule that out as a problem.

RS list a copier, would that be the way to go? Is there code protection on these chips?

Cheers Geoff

Hi Geoff

Those chips are NOT processors. They are READ ONLY memory chips, each holding 32K bytes, which is equivalent to 256K bits. Here is a typical datasheet:
https://rocelec.widen.net/view/pdf/p6ig9bhsmu/MCHPS04540-1.pdf?t.download=true&u=5oefqw

If there is a processor on that board, you need to work a bit harder to find it. Since they don't make these chips anymore you're going to have to try the Gray Market where prices are often unpredictable and potentially astronomical.

 

I see , thanks that explains why I couldn't make much sense of it!
That chip is the only one on the board that is easily removable and I know there are several different versions of it available.

There is a micro too, could the EPROM be holding configuration for the micro?

There's a few on eBay, how much UV does it take to wipe them? I have a old exposure unit for making PCBs.

I think I'll swap the eprom from one board to the other, if it works I could try wiping/reprogramming the one that doesn't.

Thanks Geoff

 

Seems I might need a MINIPRO-TL866A or similar not sure why the text changed!
Don't suppose anyone has one they'd like to sell?!

 

I see , thanks that explains why I couldn't make much sense of it!
That chip is the only one on the board that is easily removable and I know there are several different versions of it available.

There is a micro too, could the EPROM be holding configuration for the micro?

There's a few on eBay, how much UV does it take to wipe them? I have a old exposure unit for making PCBs.

I think I'll swap the eprom from one board to the other, if it works I could try wiping/reprogramming the one that doesn't.

Thanks Geoff

At 32K bytes I think there is more in there than configuration. It is likely a complete program that implements the functionality of the device. The UV erasable parts are sensitive to a particular wavelength of UV light. IIRC it is 253.7 nanometers, you need about 30 Watt-seconds/cm² to fully erase all locations. Other sources indicate that anything less than 400 nm will work but require different amounts of time for full erasure.

 

It would be useful for you to post a photo of the entire board.

 

Seems I might need a MINIPRO-TL866A or similar not sure why the text changed!
Don't suppose anyone has one they'd like to sell?!

Why are you shouting? What is that? What is the relationship between that and a 27C256?

 

Sorry about the shouting! I'd copied across from eBay, it's a EPROM copier/programmer.
I'll grab some pictures this morning, just been studying the data sheet (thank you), would it be feasible to program a pic to read from one and program another?

Few doubts I have, to program vcc has to be 6v guess this means the data output will be 6v, more than the pic16f1779 I have handy would like on its inputs?

The flow chart shows verification of each byte, the program section mentions writing the array then verifying it?

Any thoughts on programming these?

Thanks Geoff

 

Hi Geoff,
Post a link for the programmer you have seen on eBay.

This is a clip from the 27C256 datasheet, note the high programming voltages.

E

BTW: what type is the onboard micro controller IC, a photo would help.

E

 

Here is the offending board,

Here's what's happened!
I have 3 boards all together,
Board one works

Board two had a voltage regulator problem and destroyed most of its ic's

Board three I bought as working?!

I'm barking up the wrong tree with the eprom, put board 3's eprom in board 1 this morning and it all works.

Put board 2's EPROM in board 3, definitely doesn't work.

The rotary switches should change the address of the board but board 3 refuses to change, board 3's eprom in board one will change.

I'm investigating the switch's at the mo but they seem ok.

Main processor is a 80c32

Thanks for everyone's help
Geoff

 

If you have verified that moving around the 27C256 EPROM fixes the problem then here are some options moving forward.

1) Get a professional shop to make a duplicate EPROM.
2) Find someone who can do this for you.
3) Beg, borrow, or buy an EPROM programmer capable of reading and programming 27C256 EPROM.
4) Build your own EPROM programmer.

Your first step would be to copy the contents of the "good" EPROM.
You can also copy the contents of the "bad" EPROM and compare it with the "good" EPROM.

You can build your DIY programmer using an Arduino board.
You will need 8 data lines, 15 address lines, and 2 control lines. If the Arduino does not have sufficient I/O pins, you can multiplex the address lines using one set of 8 pins. Going even further, you can multiplex data and address lines using a group of 8 pins, plus additional pins for multiplex control.

 

In the absence of being able to find much wrong with it I've put it in the airing cupboard, it's been on a farm for 20+ years so thought some damp may have got in somewhere!

 

Depending on how important and critical this is to you, I can do it. You would have to send the EPROMs to me but it would not be accomplished overnight. It would take me a couple of months to get the equipment in working order.

Perhaps, there is another member here on AAC that has an EPROM programmer ready to go.

 

Thanks, unfortunately the problem lies elsewhere on the board, the eprom works as it should on the 'good' board.

I've been trying to find some instructions but Alfa Laval keep everything very tight.

The processor must be alive as the green led flashes, the whole thing seems very complicated for what it does but guess I've learnt stuff in a easier time!

Thanks again Geoff

 

Depending on how important and critical this is to you, I can do it. You would have to send the EPROMs to me but it would not be accomplished overnight. It would take me a couple of months to get the equipment in working order.

Perhaps, there is another member here on AAC that has an EPROM programmer ready to go.

Thank you that's a very kind offer

 

Still plugging away at this board!
From fiddling with the good one, on power up it gets its node address first, two red led are lit the go out.

Once powered you can alter switchs but node address won't change until power up.

The faulty one has two red led lit all the time.



Shown are rotary dip switches and a 74hct573 buffer, I assume the component to the left are pull ups for the input of the buffer?

Comparing boards the inputs change as they should do the dip switches are ok?

Is there any way to check the buffer? Short of taking it out and replacing it?

I guess the micro enables the buffer reads output and disables it as there are least 5 buffers on the board!

Thanks Geoff

 

Just been prodding with multi meter pin 11 (latch enable) is 650ohms to ground on two buffers and 1700 on the others?
Are these buffers given to failing? It's quite old but quite expensive so I don't want to ruin anything!

 

What function do the two rotary switches play?

 

Those light grey terminal blocks connect to 4-conductor cables going out of the box.
What are the cables connected to?

 

They set the node address, 0-99
They're 6pin binary encoded so one does the lower nibble on the buffer and one the upper.