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MC146814 (286 motherboard repair)

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jh1523

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I'm looking for a datasheet for this chip MC146814AP for a 286 motherboard I'm trying to repair. I believe the chip is defective but don't know exactly what its functions are. I couldn't find much information by googling; there are some mentions that it may be a RTC, but I wonder if it has other functions as well, such as NVRAM for CMOS settings etc - as it's too big for a plain RTC. The motherboard doesn't POST and this chip gets very hot very quickly after I connect power.

FWIW the motherboard is a DTK PTM-1230 The chip is the one marked KBD on that picture.
 
Hmm, I found some snippets of old Linux code that indeed refer to this chip as a RTC, not keyboard controller. Far from real documentation unfortunately. There is another large chip right next to it labeled M5L8042, I believe that's a microcontroller and more likely to be the keyboard controller.
 
jh1523 said:
I'm looking for a datasheet for this chip MC146814AP for a 286 motherboard I'm trying to repair. I believe the chip is defective but don't know exactly what its functions are. I couldn't find much information by googling; there are some mentions that it may be a RTC, but I wonder if it has other functions as well, such as NVRAM for CMOS settings etc - as it's too big for a plain RTC. The motherboard doesn't POST and this chip gets very hot very quickly after I connect power.

FWIW the motherboard is a DTK PTM-1230 The chip is the one marked KBD on that picture.
Click to expand...

Most likely it is RTC, more frequently AT used MC146818, but MC146814 appears to be the same (or compatible) thing. At least Ralf Brown's interrupt list says so. So Google for MC146818, it should be easy to find.
Normally defective RTC shouldn't prevent AT from POSTing. But you might not be able to boot it properly :)

Edit: I found a picture of your board (hopefully): DTK PTM1230.jpg

The 40-pin U62 M5L8042 chip is the keyboard controller. If it is defective, system might not boot at all, as it controls things like CPU reset. But note that this chip is manufactured using older NMOS process, and it is OK for it to be hot to touch (50C or so... you should be able to hold your finger on it for a few seconds without getting burned).
The 24-pin U56 MC146818AP chip is the RTC. One note about RTC - it uses a NiCd battery (on the right side of it), and these batteries leak over time, and its electrolyte will "eat" PCB traces and ICs' pins. So make sure to inspect your board for any damages. It is also recommended to unsolder the NiCd battery, and replace it with 2xAA or 3xAA batteries (there are multiple threads on that in this forum).
 
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I believe that the 814 is first-cousin to the 146818, which is the original CMOS memory and clock module for the PC AT. It wouldn't surprise me if they differed only slightly.

If this were my board, I'd just plug in one of the Dallas RTC modules and be done with battery worries. I've done this with other 286 boards and it works fine.
 
Yes, that is my board. The battery has been removed a long time ago, but not before leaking and doing some damage in the area of the RTC. Like I said, the RTC chip becomes very hot as soon as I power it up, which none of the other chips do. I was hoping to find a functional description/pinout of the chip so I try to replace it with something else. The keyboard controller M5L8042 does not get hot.

(I am a mortal enemy of NiCd batteries, at least those used on motherboards. I execute them on sight. They have other uses, for instance nothing holds a candle to them when used for solar-powered garden night lights. For that use, NiMH or Li cells don't come even close)
 
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jh1523 said:
Yes, that is my board. The battery has been removed a long time ago, but not before leaking and doing some damage in the area of the RTC.
Click to expand...
Sounds like there might be some trace damage. Replacing chips certainly won't remedy that if it's the problem.
 
Would the Landmark diagnostic ROMs http://www.minuszerodegrees.net/supersoft_landmark/Supersoft Landmark ROM.htm be useful in this system to diagnose the defect? I assume I would have to use the 5170 images since the motherboard has 2 bios chips, but which of U27 and U47 is "odd" and which is "even"? I do have the capability to burn my own EPROMs.

(edit) Oops, the even/odd is in the names of the files. :p Again though, would they work in this motherboard? How about in a generic 386 clone which I'm also trying to repair (more details to follow)?
 
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