127A0079C DIP28 data sheet

[KevinW]

Looking for this data sheet, can't find it on line.
It's a micro chip for a garage door opener.

Thanks.

 

[jambo6984]

When looking for pdf datasheets it's handy to just type the first number or top number and type PDF after on google usually will pull up a result if not you might have to contact manufacture but here it is found it for you

 

[jambo6984]

http://www.hkinventory.com/p/d/127A0079C.htm

 

[Ian Rogers]

That link produces no datasheet...

Normally garage doors use Holtek micro's Most wireless systems use the HT12a or 12e... ( these are encoders )

I can't find out if the 28 pin markings match that though!! The Holtek skinny 28 pin was an 8051 compatible anyway!! You need to trace the pinout and tell us where the pos and neg's connect..

 

[jambo6984]

Do you know the manufacture because if you do I don't contact them directly and they could print one out or email one, I will keep looking for you though I'm sure I can find it somewhere I know how frustrating it can be I will try a search to try to find out who is the manufacture if u can't find a actual datasheet I will go all the way to UT this time instead of believing in the description that there is one hope u can help you

 

[jambo6984]

http://www.ic2ic.com/search.jsp?sSearchWord=127A0079C

 

[jambo6984]

Here is another link to a bunch of that kind after you scroll down and click on the one that says dip 28 it may not be there but figured I would give you something while waiting on your response does it say any other numbers on it other than that a flashlight works better to read small numbers than a magnifying glass I just wanted to wait on your response before proceding with last resorts tomorrow any other info as far as brand name any other numbers or letters will help if you just need to know ground and power though if you still have the circuit board it came from you could possibly trace the lines hopefully we will find the datasheet or the manufacture before it gets to that luckily there's only a couple of manufactures that make that kind of IC probably just outdated but we will get it one way or another

 

[jambo6984]

http://www.pdficdatasheet.com/index.php?route=product/search&search=127A0079C

 

[KevinW]

You need to trace the pinout and tell us where the pos and neg's connect

I'll try and do that Ian.
View attachment 108607
https://sep.yimg.com/ay/yhst-16416632405890/liftmaster-chamberlain-41d4674-20-garage-door-opener-circuit-board-5.gif

Can anyone familiar with garage door openers indicate what the purpose is for the two small relays I have marked 1 and 2?


The trace was burnt off leading to #2.

 

[Ian Rogers]

That's a Microchip Pic... It looks like a standard 28pin , crystal on pins 9 and 10.. Resistor on pin 1.. The pic16C77 comes to mind.. But it won't be readable..

The two relays will probably be for direction.. You need to show the track side as well..

 

[KevinW]

It's one of the directional controls that's failing.
When the contacts close it doesn't trip and stop, it just continues on in that direction.
I've traced that lead back into that chip.
I pulled the relay and it is functioning properly.

 

[Ian Rogers]

When the contacts close it doesn't trip and stop, it just continues on in that direction.
I've traced that lead back into that chip.

Via one of those transistors I hope.... Pic will not power those relays...


BUT!! Those repairs are coming from the HV side...

 

[KevinW]

The center threaded nylon screw turns and moves the contacts forward and rearward.
It's the brown lead that fails to work when the contacts meet.
That brown lead can be traced back to the chip.

 

[Ian Rogers]

Okay, so its just the limit switch input... If its connected directly to the micro ( bad design work) then the micro pin must be kaput!

 

[KevinW]

I pulled the other remaining relays and they both work fine.
There is a light on the board and from what I have read 5 blinking lights indicates a faulty relay but the relays are good so it must be something else.
If you follow the white dots you can see the trace from the brown wire ends up in the chip via one resistor.

 

[Ian Rogers]

Is the resistor in the track ok? If it is, then the chip is broken.. The other check is to trace the other side of the switch... Making sure it switches the pin from 5v to 0v..

 

[KevinW]

The resistor is fine Ian.
I gave the board a thorough cleaning and it's now working.
I tried it a few times without failure and will continue to test it.
As of right now it appears to be working.
Thanks for your assistance, I'll keep you informed of the results.

 

[KevinW]

Still failing but intermittent.
When it moves to the left towards the brown wire which appears red in the picture it should stop and reverse like it does but when it fails the contacts close but the relay doesn't switch and reverse to make it move to the right.

 

[KevinW]

Just to update, the fault is caused by a defective led controlling a photo transistor on the rpm sensor.
https://www.ebay.com/itm/CHAMBERLAIN-LIFTMASTER-SEARS-RPM-SENSOR-41LG291A/201974085103?_trksid=p2485497.m4902.l9144