How to Use an A2320

[raoulduke]

I was going to ask about caps.  I think there are really just those two (http://amiga.resource.cx/photos/a2320,1), but I can replace them.  They smell fine but without (your) help I don't really know how to diagnose any of the issues with the card.  I can replace the two caps though.

Matt_H I didn't realize you were working on the assumption that it might be a PAL issue; I could have told you it wasn't.  I got it from its original owner here in New Jersey.  But he hadn't used it in a long time; I'm not sure he realized what condition it was in (regardless of the card), and it also had battery corrosion damage.

Is it possible that traces around the battery affect the display port?  My other thought in addition to the card itself was that the port may not work (properly).

And as for the cable; I just realized I bought a 23-pin to 9-pin VGA... so... but it'll make it slightly easier to graft a homebrew adapter onto the end of it.  Part of the circuit diagram for (essentially) the silverbox is here: http://eab.abime.net/attachment.php?attachmentid=16650&d=1211448710 , and you add a 100uf according to them cap between the VCC and GND.  What does that mean 5v 100uf, then?

And the silverbox looks like it also has extra circuitry on the underside.  What's the deal with that and how limited would that homebrew adapter be?  (http://eab.abime.net/showthread.php?t=36781)  I feel like they were saying it wasn't working properly at 15khz; does that mean it'll only work at 30khz?  Or ... what am I missing here.  Is it just not possible to adapt to VGA...?

[QuikSanz]

The 2 you see are of electrolytic type but, every part with a "C" in front of the part # is a cap. All types can go bad after 26 years.

Edit: I count about 32

[Oldsmobile_Mike]

What does that mean 5v 100uf, then?

It's an electrical measurement.

https://en.wikipedia.org/wiki/Farad

[raoulduke]

No, oldsmobile_mike what i meant was that the actual discussion of the schematic mentions adding a 100uf cap but it doesn't list a voltage measurement.  I was curious if someone with more electronics knowledge could infer what the voltage is supposed to be - and I was suggesting that it might be 5v but that is truly a guess.

//

Also the LCD I got the other day can do 30khz and 50hz so I think it'll work.  I didn't realize those other caps were apt to go bad.  On most of my older machines that use those types they've never gone bad.  But I suppose it's possible.  Still for the moment I'd prefer to just be able to ditch the composite output; I've had the amiga sitting on my floor in front of the tv for a week or two.

[QuikSanz]

Look again. VCC to ground, Pin 23 is VCC = +5V. They want this in the adapter for a trash filter on the power to the chip.

Edit: A bit large for that. Maybe typo, 10Mf maybe.

[raoulduke]

I understand.  I studied electronics a little bit as a young child, but I don't understand the impact of what you're saying.  Are you saying my inference that it needs a 5v 100uf cap was correct, or that it was incorrect?  Better still... could you just please tell me what the answer is?  

[QuikSanz]

Se edit, yes your assumption is right, 5V, but I question 100Mf. Sounds high to me but the voltage on that bus may have some other heavy current loads causing a fluctuation.

[raoulduke]

Thanks; as I said, I really don't know... I'm taking that discussion at face value - as I said because I just don't have the knowledge.  If someone has one of those silverboxes and can check the cap that'd possibly be useful; but I think it's got different circuitry.  [And I couldn't make out a rating in the pics on the site Matt_H posted.]

I mean... I guess putting a cap with too high a rating isn't likely to do damage, right?  (Whereas I think the other way around possibly could?)  I'm happy to experiment a little; wait and what would it possibly damage - the monitor?  I honestly don't care about that.

[QuikSanz]

This cap is only designed to keep power clean so 100Mf won't hurt, just have to wedge it into the adapter. Big size diff between 100 and 10.

[raoulduke]

I appreciate it.  Thanks.  I have spare PCB; I guess I'll buy a female vga connector - or I may have one, actually.

One last question: The 9-pin vga has a sync ground and separate R, G, and B grounds; the 15-pin vga only has one ground (that hits multiple pins).  So should I just 'tie up' all the separate grounds and just put them all to the single ground of the 15-pin?

[raoulduke]

[Well that's my plan for the grounds.]

Yeah so much for last question... Re: the A2320 and recapping, if I'm reading this: (http://www.mouser.com/catalog/supplier/library/pdf/avxmultilayerceramicld.pdf) correctly, it seems to be that the codes are highly dependent on the type of cap.  And I don't know enough to differentiate the caps on the a2320; they should all be visible in the hi-res pics posted earlier [at least to see the types].

The only one that looks substantially different in type from the others is the "101".  And one of mine looks "chipped" or maybe even zapped, subtly though.  So that one would be what I'd replace first and then test before recapping the rest.  Anyway, any help would be much appreciated, but I want to leave the list up in case anyone else wants to recap in the future.

// I don't know if any of the first bit is right...

Code         / #of Caps / Meaning
A5E 104M / 13           / 5V 0.1uf; +/- 20%; tolerance control
476 +16k / 2             / 16V 47 uf
101          / 3             / 0.1nf
019 A5M   / 4             / 5V ?; AVX; +/-20%
334 E5Z    / 3             / 5V 0.33uf; +80%; tol. cntl.
102 C5K    / 1             /
101 A1[4?] / 1
040 ACF    / 1
043 AAM   / 1
045 ACP    / 1
001 AMF    / 1
010 ANP    / 1

And then those two electrolytic caps are 16V 470uf.

[QuikSanz]

I appreciate it.  Thanks.  I have spare PCB; I guess I'll buy a female vga connector - or I may have one, actually.

One last question: The 9-pin vga has a sync ground and separate R, G, and B grounds; the 15-pin vga only has one ground (that hits multiple pins).  So should I just 'tie up' all the separate grounds and just put them all to the single ground of the 15-pin?

It appears as though the 15 pin has 3 grounds next to RGB pins, so 1 for each color, to keep out crosstalk/color bleed. #5 should be power ground, that's the ground you want.

[raoulduke]

"Normally," though, I think they're wired together anyway.  Usually that second row and then a few first and third row pins are wired together.  I can't find my d-sub female connector (to evidence that thought), but: http://www.blogcdn.com/www.engadget.com/media/2006/11/vga_pinout.jpg .  But I can wire them specifically to the pins near the R, G, B; no biggie.  [I am a little curious if that explains a quality issue with my ST adapter, though.]

[QuikSanz]

I suppose the layout is for all formats including RCA type cable just put the cap near the chip close to the legs. Maybe underneath.

Edit: Use electrolytic

[raoulduke]

Cool.  Thanks.  I couldn't find 5v 100uf caps at mouser or digikey, so I'm going to go with 6.3v.

I think I'll actually make a little PCB connector board and leave the cables detachable on both ends.  I've had not great luck with my 8 or 9-wire Atari ST bus mouse adapter.

[raoulduke]

Didn't work [my VGA adapter]... I guess there's a small possibility that I wired it wrong (which I think is unlikely, though) and that starting from scratch would help.

Actually the only thing I couldn't try is the Dell CRT monitor I bought that has (by a wide margin) the widest scanning range - bc it has a male VGA plug and my ... apparatus ... also has a male VGA plug.  So I think I'll start there (with an adapter).

I recapped the two electrolytic 470uf 16V caps on the A2320 but that had no obvious effect.  I bought these 101(-labeled) caps but the ones I got only have two axials/leads and the originals have three.  Is one a ground?  I assume I should just look for another set of caps that have 3?