27C256DC-12 duplication and Atmel 80C32 fault finding

Thread Starter

geoffers

Joined Oct 25, 2010
475
I'm more getting curious than anything else!

Next to the 74hct139 is a 74hct00e which is a NAND gate.

Output y1 of the nand drives one of the inputs of the 139. From 2 processor pins?? (24&28)

What is the logic behind using 2 pins to one pin on a device intended to multiply outputs?

I know I've missed something

Cheers Geoff
 

ericgibbs

Joined Jan 29, 2010
18,766
Hi Geoff,
You could start adding circuitry to this image.
It would help you develop the circuit diagram, post your sketches and I will tidy them up.
E
Geoff1.gif
 

Thread Starter

geoffers

Joined Oct 25, 2010
475
Thanks Eric,

Your quite right, I've been looking at all my bits of paper thinking I should map out the whole darn thing, I'll fire up design spark this afternoon and see what pickle I can create!
 

Thread Starter

geoffers

Joined Oct 25, 2010
475
What's the best format to post schematic diagram in?

Can do design spark .sch, bitmap or I think it's metafile

Which is clearest? I tried a bitmap but couldn't zoom in very well, I've mapped a reasonable bit of it but takes a while.

Cheers Geoff
 

ericgibbs

Joined Jan 29, 2010
18,766
hi G,
I use Gif, bmp, jpg , try posting a dummy try image.
E

Edit:
do you have a screen capture program?
 
Last edited:

Thread Starter

geoffers

Joined Oct 25, 2010
475
Still plugging away slowly,
Replaced the 74hct139 and 74hct00
The light show has changed but still not right, I've turned my attention towards the inverter 74hct04 to the left of the processor, one of its outputs is le on the right hand 74hct573, it looks to the untrained eye when the program is running like the wrong latch is being used so I've ordered one and will change that, I've also ordered 5 latches and will change them if need be!
 

Thread Starter

geoffers

Joined Oct 25, 2010
475
Update!
I've mapped out where the 74hct04 goes and replaced it. Still doesn't function properly but longer between reset pulses.

Leads me to ask, when a circuit like this fails (cause unknown) can a fault on one chip take out a few others? Or is it likely to be a voltage spike and pot luck which survives? I've five 74hct573 latches coming which I will change, hopefully today, after that there is only one logic chip left, and the bus interface chip which is as far as I know completely unavailable!

Cheers Geoff
 

Thread Starter

geoffers

Joined Oct 25, 2010
475
Update!
Replaced the 2 74hct573 latches between the processor and eprom.

The green light no longer flashes

A red light comes instead

I think that's trying to tell me it's not got it's node address so I'm going to change that latch next.
 

Thread Starter

geoffers

Joined Oct 25, 2010
475
Another update!
All latches changed now, the red light takes longer to come on now but still does!

The last remaining logic ic is a 74hct151 multiplexer which interfaces with the RFID readers I believe, it's E input and y output are connected to the processor and reading the data sheet a high input on E forces Y low.

I'm just hoping this is being used as a error check and is causing my red light!

Other than that it's the bus interface chip left, I can't get that.

Fingers crossed, have a 74hct151 on its way.......
 

Thread Starter

geoffers

Joined Oct 25, 2010
475
Final?! Update.

I hope that's it anyway! Thanks to Mr chips and Eric my circuit board is currently working!

Very pleased, still wonder what might have caused it though? Every logic ic seems to have failed along with the processor, only ones to survive where the eprom and bus interface.

Got in touch with the chap I got it from and he reckons was still working when removed!!

Cheers Geoff
 

MrChips

Joined Oct 2, 2009
30,711
Final?! Update.

I hope that's it anyway! Thanks to Mr chips and Eric my circuit board is currently working!

Very pleased, still wonder what might have caused it though? Every logic ic seems to have failed along with the processor, only ones to survive where the eprom and bus interface.

Got in touch with the chap I got it from and he reckons was still working when removed!!

Cheers Geoff
Not necessarily all failed.
You replaced many that could still be working. You eventually replaced the bad ones.

Congratulations on a successful repair job!
 

Thread Starter

geoffers

Joined Oct 25, 2010
475
One more question......

Re varnishing the PCB, rs do PCB varnish, I've cleaned off the flux with isopropyl alcohol is that enough or should I use something else?

Cheers Geoff
 
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