Author Topic: Broken Facit A3400 Serial Terminal  (Read 2406 times)

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Offline Ozric

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Broken Facit A3400 Serial Terminal
« on: May 02, 2015, 09:17:58 pm »

A while ago I came into possession of a Facit A3400 Serial Terminal from the early 1990s.

Unfortunately it is not working properly and I am not really knowledgeable enough about electronics to know what to do with it.
When I turn it on it takes about 10-15 minutes before the screen comes on. What is displayed on the screen is constantly flickering white horizontal lines:

The screen does not change or react when I hook up something to the serial interface. I can connect to it from a host device but of course I cannot really see if it works or not because I can't see any output sent from a host on the screen. The vertical lines you can make out in the photo are burn-in from whatever software this terminal used to run.

I have checked the battery in the thing and it shows the correct voltage, but that might be me getting fooled by something.

Anyone have any suggestions on what might be wrong or what I should test?

Here are some more pictures of it:

Offline SeanB

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Re: Broken Facit A3400 Serial Terminal
« Reply #1 on: May 03, 2015, 08:07:14 am »
Your monitor board and probably the SMPS has some dying capacitors.

The monitor board is on the left and the PSU is to the right. You probably will see some bulging capacitors on the monitor board, and replacing those with new ones will likely fix it.

Offline Ozric

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Re: Broken Facit A3400 Serial Terminal
« Reply #2 on: May 03, 2015, 10:41:50 am »
I took it apart again to check the caps, and I could not find any that were bulging unfortunately.
Here are some pics:

EDIT: Took another look and it looks like someone's had a little accident on the power board:

Now i just need to buy a cap and soldering iron and this terminal might just be up and running again.
« Last Edit: May 03, 2015, 10:49:24 am by Ozric »

Offline Ozric

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Re: Broken Facit A3400 Serial Terminal
« Reply #3 on: May 04, 2015, 06:30:01 pm »
So, I borrowed a multimeter so I could measure that cap and any others. However I do not know if the multimeter is giving accurate reading or not.

I am getting four lines on that leaky cap (- - - - µF) on the multimeter display but I am also getting that on a lot of the other caps on the power supply board. However some of them do show what seems to be relatively accurate values (314 µF on a 330 µF cap for example.) Could it be that a bunch of the caps on the board are broken even though they are not showing any physical signs of it, or am I being fooled by the multimeter?

The meter is a Meterman PM51.

Offline poot36

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Re: Broken Facit A3400 Serial Terminal
« Reply #4 on: May 05, 2015, 03:30:34 am »
You are seeing the common problem of trying to measure the caps in circuit.  If you unsolder one leg of the cap you can get a correct reading.  I would try and get one of the cheap ($20) component testers online that has a ESR tester built in.

Offline Ozric

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Re: Broken Facit A3400 Serial Terminal
« Reply #5 on: May 30, 2015, 05:37:19 pm »
Today I bought a soldering station, solder, wick and a big pack of caps, unsoldered the broken cap (it measured about 4.5µF instead of 220) and soldered on a new one.

It works!

Such a great feeling being able to fix this old piece of technology.

Offline Deathwish

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Re: Broken Facit A3400 Serial Terminal
« Reply #6 on: May 30, 2015, 05:42:42 pm »
Congratulations, now my personal advice is that I would replace all the others regardless of looks, it's like me, old and some of them can go anytime, best be safer than not.
Electrons are typically male, always looking for any hole to get into.
trying to strangle someone who talks out of their rectal cavity will fail, they can still breath.
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