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Author Topic: Capacitors - wrong orientation? (Read 463 times)

Online Wolfgang

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Capacitors - wrong orientation?
« on: 2020.September.16. 11:49:54 »
In both my EP64s C9 is oriented like this(minus to the left): https://www.nightfallcrew.com/gallery/enterprise-128-one-two-eight-boxed/IMG_5573.jpg

According to the schematics, the orientation of C9 should be like this (minus to the right):
https://enterpriseforever.com/hardware/ep-repair-service-)-help-with-egyptian-ep64-no-video-outputnot-strating/?action=dlattach;attach=25401;image

Why are they different?
 
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Online gflorez

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Re: Capacitors - wrong orientation?
« Reply #1 on: 2020.September.16. 12:52:21 »
I am not the better knowledge source about electronics, but observing the schematics



and this closer picture without the components(thanks to Pear),



I see the right pin of C9 tied to the central pin of U21, Ground, so the capacitor minus pin should go also to the right.

Strange to find this assembly error after so much years.
« Last Edit: 2020.September.16. 13:00:35 by gflorez »
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Online John Fante

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Re: Capacitors - wrong orientation?
« Reply #2 on: 2020.September.16. 17:51:13 »
Hmmm. Interesting. When I did my recap Ioriented my new C9 as it was on the board. + to the right. So I have the same layout as Wolfgang.

Here are the old. And here the new.

Not to hijack the thread but maybe this error is causing my noise. If it is an error, that is!
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Online Wolfgang

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Re: Capacitors - wrong orientation?
« Reply #3 on: 2020.September.16. 18:25:11 »
Quote from: John Fante on 2020.September.16. 17:51:13
Hmmm. Interesting. When I did my recap Ioriented my new C9 as it was on the board. + to the right. So I have the same layout as Wolfgang.

Here are the old. And here the new.

Not to hijack the thread but maybe this error is causing my noise. If it is an error, that is!
I actually turned the new C9 around, since it seems the correct orientation to me.
No real difference to see (yet), at least no smoke and interesting smells.:razz:

Btw., no reason to apologize, I am in the same boat. I also got an Egyptian EP and I am trying to get it up to speed. So far, I upgraded the ROM to EXOS2.4 and built my memory expansion. Now, I am fighting the missing color of the RF signal.:smt017
« Last Edit: 2020.September.16. 22:31:00 by Wolfgang »
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Offline Judge

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Re: Capacitors - wrong orientation?
« Reply #4 on: 2020.September.16. 19:26:05 »
Quote from: John Fante on 2020.September.16. 17:51:13
Hmmm. Interesting. When I did my recap Ioriented my new C9 as it was on the board. + to the right. So I have the same layout as Wolfgang.

Here are the old. And here the new.

Not to hijack the thread but maybe this error is causing my noise. If it is an error, that is!

Despite appearances, this is good orientation...

25465-0

25467-1
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Üdv.Judge

Online John Fante

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Re: Capacitors - wrong orientation?
« Reply #5 on: 2020.September.16. 20:45:01 »
Quote from: Judge on 2020.September.16. 19:26:05
Despite appearances, this is good orientation...

(Attachment Link)

(Attachment Link)

Ok. So the way it is mounted originally is the right way - despite what the schematics say? :)
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Offline Judge

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Re: Capacitors - wrong orientation?
« Reply #6 on: 2020.September.16. 22:16:29 »
Quote from: John Fante on 2020.September.16. 20:45:01
Ok. So the way it is mounted originally is the right way - despite what the schematics say? :)

ZoZo wrote here on the forum about this long ago what is the reason ...:smt017
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Online Wolfgang

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Re: Capacitors - wrong orientation?
« Reply #7 on: 2020.September.16. 22:26:21 »
I don't think that the schematics are wrong.
In fact the capacitor in this  image

is strange. The - arrows point in the direction of the narrowing, opposite to the usual way. Since the visible right side of C9 seems to be metal, I would assume that this is the GND side.

To sum it up, I think
- the right side should be minus
- the arrow on the capacitor in the image above is wrong
- the capacitor in the image above is mounted correctly (+ left / - right)
- the silk screen on the pcb seems to be wrong

I am not an electronics expert, so please convince me that I am wrong.:)
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Offline Judge

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Re: Capacitors - wrong orientation?
« Reply #8 on: 2020.September.16. 23:06:31 »
This is the same motherboard with the original capacitors ... The + seems to be pointing to the right...and so on all the EP motherboards I have seen

25469-0
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Online gflorez

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Re: Capacitors - wrong orientation?
« Reply #9 on: 2020.September.16. 23:31:02 »
I think that Judge could be right.... and the schematic wrong.... if there is negative voltage at the left side, GND is positive.
« Last Edit: 2020.September.16. 23:44:16 by gflorez »
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Offline Judge

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Re: Capacitors - wrong orientation?
« Reply #10 on: 2020.September.17. 00:22:04 »
We are waiting for ZozoSoft.. once he told me why this is so ... :)
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Offline elmer

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Re: Capacitors - wrong orientation?
« Reply #11 on: 2020.September.18. 05:02:35 »
Quote from: Judge on 2020.September.17. 00:22:04
We are waiting for ZozoSoft.. once he told me why this is so ... :)

I'm quivering with anticipation, waiting for his reply! ;)

I did a search on forum, looking for all references to "C9", but it didn't turn up any satisfactory explanation.
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Offline Judge

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Re: Capacitors - wrong orientation?
« Reply #12 on: 2020.September.18. 08:00:14 »
Look at the sign on the planting scheme...

25479-0

25481-1

25483-2
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Online Wolfgang

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Re: Capacitors - wrong orientation?
« Reply #13 on: 2020.September.18. 11:06:51 »
Quote from: elmer on 2020.September.18. 05:02:35
I'm quivering with anticipation, waiting for his reply! ;)

I did a search on forum, looking for all references to "C9", but it didn't turn up any satisfactory explanation.
Same here. :)
All available (different) schematics show the same direction.
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Offline BruceTanner

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Re: Capacitors - wrong orientation?
« Reply #14 on: 2020.September.18. 17:01:26 »
I can confirm that the PCB markings are correct.

On a working EP, with the ground clip of an oscilloscope probe connected to the right side of C2 (0V) and the tip connected to the left side of C2, there is approx -1v across the capacitor ie. the right side is more positive than the left side. Except for a few ms at powerup :oops: which might explain why C2 is a common failure.

25485-0
Here purple is 12V,  blue is 5V and yellow is across C2, at power on (note different v/div for each channel.)

I was looking at power on because I thought the purpose of C2 might be to delay 12V coming up so that 5V comes up first. But here you can see that the 12V trace reaches 9V almost immediately and then goes to 12v ~3ms later, so I'm still not 100% sure! :lol:
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