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Old 06 May 2012, 10:58   #1
8bitbubsy
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Ricoh RTC diode in Amiga 4000

Some of you might have seen this big 1N5817 diode connected from the VCC pin on the RTC to an SMD component on many Amiga 4000 motherboards -- any idea what this fix really does? My rev B Amiga 4000 mobo never had this one, and I was wondering if I should install this diode myself...

Here's a picture of what I mean:

Last edited by 8bitbubsy; 14 December 2012 at 18:43.
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Old 06 May 2012, 12:19   #2
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Quote:
Originally Posted by 8bitbubsy View Post
Some of you might have seen this big 1N4001 diode connected from the VCC pin on the RTC to an SMD component on many Amiga 4000 motherboards -- any idea what this fix really does? My rev B Amiga 4000 mobo never had this one, and I was wondering if I should install this diode myself...

Here's a picture of what I mean:
I cant remember what it fixed but it does fix something. Have'nt done one for a while now, hence I cant remember what it fixes.

I think it was a fix to stop a boot related problem.
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Old 14 March 2013, 12:40   #3
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Bumping this thread.. Can someone with an A4000D (which has this diode) check what diode type it really is? The number starting with 1N. I'm not sure if it was a 1N5817 after all...
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Old 14 March 2013, 13:32   #4
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Dont know if this helps:

@28/05/10
Very strange problems may create a defective Ricoh 5C01 real time clock IC, as red screen, yellow screen, or not boot at all.
Also recently encountered a very strange problem was as follows.
In an A4000 who boot normaly from cold start and work perfect, if someone push off and on again the mains switch, has as result a dark grey screen. After two minutes with the machine OFF, when the restart all work perfect again!!! This was repeated.

The problem was the Ricoh ic. For some reason degrade its suply voltage from +5v, to 1.77v!!!! This was happened only if someone shut and then restart the machine from a previews working condition.

At first I think cause the ic was defective, but later discover cause in some pcbs, must add a 1N4001 diode from D178, to Ricoh ic at pin 20. The cathode of diode must connect at pin 20 of ic.

Source: http://www.amibay.com/showthread.php?t=6896

Last edited by Turran; 14 March 2013 at 13:38.
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Old 14 March 2013, 14:22   #5
8bitbubsy
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Thanks!

Anyways LOL I just noticed something... On all Amiga 4000D's, the L and R label is wrong... It should say R and L, but instead it's swapped.
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Old 14 March 2013, 14:29   #6
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Same with mine and another one I know of =) Labels are correct, color is not.
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Old 14 March 2013, 19:49   #7
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Quote:
Originally Posted by 8bitbubsy View Post
Bumping this thread.. Can someone with an A4000D (which has this diode) check what diode type it really is? The number starting with 1N. I'm not sure if it was a 1N5817 after all...
Check reverse current for 1N5817 - it doesn't look good - IMHO this can't be Schottky as reverse current in Schottky diode is to high.
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Old 15 March 2013, 10:54   #8
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The diode is in original state 1N5817.
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Old 15 March 2013, 17:00   #9
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reverse current for this diode is around 1mA - battery can be drained quite fast...
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Old 17 March 2013, 09:50   #10
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Quote:
Originally Posted by Turran View Post
Same with mine and another one I know of =) Labels are correct, color is not.
Just about all of them have the colours reversed. As a result I remember having a big arguement as a kid with an a4000 owning friend regarding whether red is right or not. :-D
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