Rev 7 Motherboard A500

[77slevin]

I dug up my first Amiga 500 Motherboard from the back of my closet and decided to restore it to its full glory. While researching the board I don't find much info on the revision 7, which it seems I have. Was this a limited released version, with not much boards sold, because I did see there was a version 8 with much more information to be found. Can someone on here shine a light on this?

[Jope]

Yes, very limited. It's a rather old revision, apparently made pretty soon after rev 6. For some reason they decided to continue mass production with rev 6 until the rev 8 board was needed for the new 8375 Agnus.

What date codes are on the yellow sticker and on the chips on your board?

[77slevin]

Originally Posted by Jope

Yes, very limited. It's a rather old revision, apparently made pretty soon after rev 6. For some reason they decided to continue mass production with rev 6 until the rev 8 board was needed for the new 8375 Agnus.

What date codes are on the yellow sticker and on the chips on your board?

I will check and post it tonight. Knew something was up with this when I checked the usual resources.

[77slevin]

Dates are 87/88 see pictures


Full board: https://imgur.com/gallery/uZxC2Fg


detail rev7: https://imgur.com/gallery/HG1v8bq

I'm really surprised there are no bulging capacitors to be seen on the board. Then again the super bad ones were probably from early 90's, with the A1200 and A600...

[eXeler0]

cool, could you snap some more closeups so that we can see revisions of the chipset components?

[77slevin]

This is what I can do short term, a bunch of camera pics:https://imgur.com/a/VIrsrgW

Planning to make some decent photos by daylight this weekend, with a decent camera.

Might also send a few to http://amiga.resource.cx/ if it is still being maintained. I noticed the Gen 7 entry was without photos

[Sim085]

So where there any differences between rev6 and rev7?

[eXeler0]

Originally Posted by Sim085

So where there any differences between rev6 and rev7?

From the pics provided, I'm struggling to see any difference between this rev 7 and say a rev 6A.
There's a marking that says 8839, I was thinking this is maybe week 39 of year 88, but then the the 6A mobo shown here http://amiga.resource.cx/ has a date stamp of week 41, 1988.
The rev7 also seems to have a lower serial number.
I's like a better photo of the upper right part of the mobo if possible though, @77slevin

To summarize, the rev 7 actually seems to pre-date the rev6a so maybe there was just some glitch in the naming that they changed back quickly..

[duga]

Originally Posted by eXeler0

From the pics provided, I'm struggling to see any difference between this rev 7 and say a rev 6A.
There's a marking that says 8839, I was thinking this is maybe week 39 of year 88, but then the the 6A mobo shown here http://amiga.resource.cx/ has a date stamp of week 41, 1988.
The rev7 also seems to have a lower serial number.
I's like a better photo of the upper right part of the mobo if possible though, @77slevin

To summarize, the rev 7 actually seems to pre-date the rev6a so maybe there was just some glitch in the naming that they changed back quickly..

And 8836 on the CPU.

Different factories? Or they made 7 for a while but decided to go back to rev 6?

[Marce]

Originally Posted by 77slevin

I'm really surprised there are no bulging capacitors to be seen on the board. Then again the super bad ones were probably from early 90's, with the A1200 and A600...

they used japanese caps in the A500 /A2000/A3000, caps that basically last forever,in the A600 A1200 they inserted chinese craps , unless 1 Elna 470uf, 10v (the only good one)

[Daedalus]

Originally Posted by Marce

they used japanese caps in the A500 /A2000/A3000, caps that basically last forever,in the A600 A1200 they inserted chinese craps , unless 1 Elna 470uf, 10v (the only good one)

They used whatever capacitors were cheapest at the time in basically all their models. The difference is the later models (e.g. A600 and A1200) use SMT capacitors whereas the older models use through hole, and this is where the issues come from in the later models. Where the capacitors were made doesn't really factor into it - plenty of Chinese capacitors were used in the older models, and there are plenty of Japanese SMT capacitors that have leaked after 25 years of use.

[Marce]

Originally Posted by Daedalus

They used whatever capacitors were cheapest at the time in basically all their models. The difference is the later models (e.g. A600 and A1200) use SMT capacitors whereas the older models use through hole, and this is where the issues come from in the later models. Where the capacitors were made doesn't really factor into it - plenty of Chinese capacitors were used in the older models, and there are plenty of Japanese SMT capacitors that have leaked after 25 years of use.

nope, for ex the A500 motherboard basically have only 2 caps, and always were chemicon or nichicon (japan)

the A1200 contain around 10 or 12 SMT chinese craps, 3 chinese electrolytic caps and 1 ELNA good cap ( for the audio)

the difference is day and night, that's why the A500 never need a recap

[nikosidis]

It would kind of make sense to go to rev. 7
Rev. 3, 5, 7
Why they suddenly went rev. 6 and 8

I never seen A500 with a bad cap.
Neither a Commodore 64.

It is the surface mount caps. that started to leak on later models. A600, A1200, A4000.
To say they are bad quality would also be questionable. After 30 years?
I would say be aware. The battery they put in some models are much worse.

[Daedalus]

Originally Posted by Marce

nope, for ex the A500 motherboard basically have only 2 caps, and always were chemicon or nichicon (japan)

the A1200 contain around 10 or 12 SMT chinese craps, 3 chinese electrolytic caps and 1 ELNA good cap ( for the audio)

the difference is day and night, that's why the A500 never need a recap

Right, so you don't really know what you're talking about then. Thought as much. I've found dead and dying capacitors in A500s before, and in Atari 8-bits (I've never recapped a C64 so can't comment there) and lots of other equipment, old and new. But the point is, all conventional electrolytic capacitors degrade sooner or later, and the reason the A500 doesn't need a recap is that when the through hole caps die, they don't spew their guts onto the PCB directly beneath them and start corroding it. SMT capacitors of that era are particularly prone to failure, regardless of manufacturer, but THT capacitors fail too, even if they last a bit longer. Also, most capacitors in an Amiga don't show any obvious symptoms when they fail, so you simply can't tell whether most of those capacitors in that A500 are still fully working or not. There are a couple though that can and do cause the machine to fail when they fail - I've repaired several A500s by replacing dead capacitors.

[Marce]

Originally Posted by nikosidis

I never seen A500 with a bad cap.
Neither a Commodore 64.

It is the surface mount caps. that started to leak on later models. A600, A1200, A4000.

this is 100% correct
in fact I still have my commodore 64 C with chemicon japanese capacitors, it works like a day 1 after 37 years or so

[Jope]

Originally Posted by eXeler0

To summarize, the rev 7 actually seems to pre-date the rev6a so maybe there was just some glitch in the naming that they changed back quickly..

I decided to take another look and the only difference I can see between rev 6 and 7 is between U33 and Denise. There is a footprint for a trimmer cap in rev 7, where rev 6 has three caps in that same area.

Seems they wanted to make the cap for 7MHz adjustable, but ended up just cost reducing it back to a fixed value. The schematics for rev 6 on amigawiki actually show a trimmer cap for C403.

The other two caps look like they are for CCK and CCKQ at the AmigaBUS slot (XC1 and XC2 on the rev 6 board) . They have been cost reduced out of the rev 7 board, but looks like they have been bodged back in between the ground at the end of missing RP405 and the respective clock pins at RP103.

Seems probable that they had designed rev6 and rev7 in chronological order, but decided to go back to rev6 for mass production due to the problems they found with the clocks after deleting the caps.

[utri007]

I have also a rev 7 motherboard. Ram chips mounting holes are all through, easy expand ram.

[Jope]

Originally Posted by utri007

I have also a rev 7 motherboard. Ram chips mounting holes are all through, easy expand ram.

Nice.. Did you find yours from a Finnish sold machine? What date codes are stamped on the chips?

[4pLaY]

I have a revision 7 as well that i got from the UK at one point. I have seen hundreds of A500 motherboards and this is the only rev 7 i can remember seeing.

[thebajaguy]

The cap in the reset circuit can dry out. The cold-boot behavior of a guru banner is typical in that case - particularly of expanded systems (sidecar and internal) that use the host PSU. The system comes out of _reset too quickly, and the peripheral hardware hasn't settled from initial power on.