Help Identifying Chips.

[Eynhallow]

Hi,
I'm new on this forum, so please tell me if I'm posting in the wrong place.
I'm trying to repair a microprocessor controlled tachometer manufactured by VDO, the from 2007, part number 02 012 195.
There are 5 chips on the board, and I need to identify them to stand a chance of fault finding the board.
I've identified the easy ones; There's a LM7805 to bring the power supply down from a nominal 12 volts to 5 volts.
A PCF8582C-2, 256 bit EEPROM.
And a LM2903, dual comparator, which I guess conditions the signal from the alternator, so the revs can be counted.
That leaves what looks like the microprocessor, and a second chip (which I'm not sure what it does)
The Tachometer has an analogue needle and an LCD to display the hours the engine has run.
I've attached two photos of the chips I'm trying to identify. I've tried the obvious google search of the part numbers, but in places it's hard to read the numbers, so I may have made some errors.
Can anyone Help?

 

[Mickster]

1st:
Could not find, sorry.

2nd:

https://www.mouser.com/datasheet/2/149/74ACT240-888464.pdf

Check datasheet to see if it matches.

 

[Eynhallow]

Thank you, 4 down 1 to go.

 

[rjenkinsgb]

I'd guess that the larger one is a custom made device or custom programmed microcontroller, rather than an off-the-shelf IC.

 

[narkeleptk]

The top ic is old Phillips logo so that may help find what it is. Its either custom as rjenkinsgb mentioned or maybe its just masked which is also very common.
I didn't look around too much but if you think its a mcu maybe check to see if this matches https://www.nxp.com/docs/en/data-sheet/8XC51_8XC52.pdf

The bottom one is Texas Instruments. maybe this https://www.ti.com/lit/ds/symlink/sn74ac240.pdf

 

[Eynhallow]

Thankyou, Yes the the microprocessor looks very like a custom version of the philip microcontroller 8xC51, which has an inbuilt timer, the PCB seems to confirm that, because the pulse from the the alternator arrive at the correct pin, after being conditioned by the comparator.
I have a picoscope, so the next thing to do is to power it up and see if I can figure out what's going on. I just hope it's something simple, which I can fix, otherwise it's £200 + for a replacement.
Once again, thanks for the help, invaluable.

 

[dr pepper]

What does the tacho do when in use, does the pointer move at all.
Does the pointer move when you jiggle the tacho.
I cant remember what make it was but I had a tacho in my boat that was driven off the alty, it had an air core movement.
If your going to scope things check for 5v and ensure the tacho is actually getting pulses from the alty, also see if the windings within the movement are receiving signals, if theres 2 or 3 coils then there might be pulses there all the time, another later type movement is an x27 stepper motor, this only gets pulses when it needs to move.
I'd be interested to see some pics.

 

[Eynhallow]

Yes, a VDO 85mm, it has an LCD (hrs) and a moving pointer, there's a moving coil driving the pointer.
It's essentially dead, nothing moving and no display on the LCD. I can't find any data on the tacho, when I plug the part number into google I can find an installation manual, but it's not for the version I have.
It's driven by a 12 pole alternator, there's a pulley ratio between the crankshaft pulley and the alternator pulley of around 2, this gives around 20 pulses per rev ( I can't remember the exact number).
When I took it off the boat it was getting power and pulses. I'm in lock down 165 miles from the boat, and I haven't powered it up since I got home, I've been marchelling all the info' I can before I start using the scope to poke around.

 

[dr pepper]

12 pole alty would be 12 or 24 pulses off one winding.
Favorite so far would be the 5v regulator, or a bad electrolytic.
If you have a relay and a cap you can make a simple mechanical oscilator to test the tacho, the cap from 100 to 2200 uF across the coil would change the freq.

 

[Nigel Goodwin]

Obviously if the processor is faulty, then he's completely stuffed.

But by downloading the assumed Philips datasheet he can see which pins are power (check those for the correct voltage), check reset (that's it's not been held in reset), and check if it's oscillating (assuming an external crystal) - make sure to use a x10 probe on the scope. If those are all OK, then check if there's and signals on the I/O's feeding the display.

Generally it's VERY rare for a processor to fail, it's mostly something external - and clock crystals failing are quite common.

 

[narkeleptk]

Generally it's VERY rare for a processor to fail, it's mostly something external - and clock crystals failing are quite common.

Don't know about that. I see corrupted flash/eeprom data and failed I/O on processors all the time in automotive modules.

 

[Nigel Goodwin]

Don't know about that. I see corrupted flash/eeprom data and failed I/O on processors all the time in automotive modules.

Might be different in automobile applications then?, possibly due to the extreme conditions?.

 

[Mickster]

It's essentially dead, nothing moving and no display on the LCD.

Might that suggest power supply, or the processor not running?
Is there any illumination on the tacho, and does it light up if so?

 

[atferrari]

But by downloading the assumed Philips datasheet he can see which pins are power (check those for the correct voltage), check reset (that's it's not been held in reset), and check if it's oscillating (assuming an external crystal) - make sure to use a x10 probe on the scope.

To avoid disturbing the oscillator, Nigel?

 

[Nigel Goodwin]

To avoid disturbing the oscillator, Nigel?

Yes, normally using a x1 probe instantly stops the oscillator, using x10 means it still works.

 

[narkeleptk]

Might be different in automobile applications then?, possibly due to the extreme conditions?.

Could be. Makes sense for many of the failing I/O's. Most of the corruption issue's are from battery related things. Constantly low/dying, charging, reverse polarity, etc..

I would expect marine applications to be just as bad if not worst.

 

[dr pepper]

I've had hc49 lareger can crystals go a few times, esp in hand held items, the tubular can style ones used in watches tend to be a lot more hardy.
To test the xtal a x10 scope probe might do the trick on the xtal itself.

 

[Diver300]

Even x10 'scope leads can stop a working oscillator. If the oscillator is less than about 25 MHz, it is likely to be running the crystal in its fundamental mode and the 10 - 12 pF of a x10 scope probe will shift the frequency by a couple of hundred ppm. That doesn't make any difference if you just want to see if the oscillator is running, but it's no good if you want to know if the frequency is as accurate as it can be.

 

[dr pepper]

Yes agreed, I've checked a processor xtal a few times with my 'scope and it hasnt stopped it, however doing so on a overtone oscillator has stopped oscillation.

 

[Nigel Goodwin]

Yes agreed, I've checked a processor xtal a few times with my 'scope and it hasnt stopped it, however doing so on a overtone oscillator has stopped oscillation.

Processors don't generally use overtone crystals, as there's no tuning - never had a problem as long as you use x10, but x1 stops most of them. A slight frequency change is no problem, as you're only looking if it's running, a scope isn't accurate enough to check frequency anyway.