Help with a dead A500?

I've got an a500 that doesn't want to wake up. Here's what it is, what I've done, and the symptoms:

Specs:
Rev 6a motherboard
8372A fat agnus
a501 in the trapdoor
JP2 shorted on the uppermost pads
JP7A open
a520 video adapter

When I first turned it on, it showed a green screen, a pulsing power LED, and no floppy activity. The intertubes suggested either bad Chip RAM, or a faulty Agnus, with reseating the Agnus as the possible fix. Tried it without the a501, and the same result.

I pulled/cleaned/reseated the Agnus, and, since I was in there, reseated the other socketed chips as well. Excercised all due caution, anti-static precautions, etc.

Tried it again, and this time there's no screen at all. My TV says "No Signal", so I believe it's not just a black screen, but who knows when a 20+ year old machine is trying to talk to the new kid TV. :)

Tried it with/without the a501, different, known good PS, verified the a520 is working well (used it on a known good a1200). So, I'm not sure if I made a bad situation worse, or if it was just a goner to begin with. :(

I'd like to get it working, and pass it along to someone who will use it (my a1200 suits me well, I just wanted to rescue this thing). Any suggestions on where to start troubleshooting it? My gut is "replace everything that's socketed", but I don't have a spare a500 to do that...

Thanks!
WhyreByter

And no A2000 around, too?

Complete dead black screen normally means dead CPU.

Sometimes just re-inserting the Agnus not cure the green screen problem if its socket get fissured.

A 68000 CPU is dirty cheap and will be the starting line to recover this A500.

Thanks, rkauer! Pretty much what I figured. The inside looks really nice, minimal dust, no cola, etc., so it should be worth saving. Anyone in the Seattle, WA area with a spare MC68000P8? :)

I need to open up the a501 tomorrow, as it still has the metal shield soldered in place, which means it's probably still got the original battery in it. No leakage outside the shield, which is good.

Thanks!
WhyreByter

---------- Post added at 19:07 ---------- Previous post was at 19:03 ----------

Quote:

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Originally Posted by WhyreByter

I need to open up the a501 tomorrow, as it still has the metal shield soldered in place, which means it's probably still got the original battery in it. No leakage outside the shield, which is good.

Thanks!
WhyreByter

---

Just peeled up a corner of the shield, and it's still got a nicad battery in it, but, amazingly, it looks absolutely brand new. But, it's still gotta go, ya know!? :lol:

Hiyas WhyreByter

lets analyze =)

Quote:

---

Originally Posted by WhyreByter

I've got an a500 that doesn't want to wake up. Here's what it is, what I've done, and the symptoms:

---

okay lets lookie at what you have

Specs:
Rev 6a motherboard (good)
8372A fat agnus (good)
A501 in the trapdoor (okay)
JP2 shorted on the uppermost pads (pad 1 & 2 = good)
JP2 Pads 2 & 3 Cut (you need to do this)
JP7A open (good)
A520 video adapter (caution these can be flaky)

Quote:

---

Originally Posted by WhyreByter

When I first turned it on, it showed a green screen, a pulsing power LED, and no floppy activity. The intertubes suggested either bad Chip RAM, or a faulty Agnus, with reseating the Agnus as the possible fix. Tried it without the a501, and the same result.

---

This is the classic memory assertion failure - there is a base conflict of address.

Quote:

---

Originally Posted by WhyreByter

I pulled/cleaned/reseated the Agnus, and, since I was in there, reseated the other socketed chips as well. Excercised all due caution, anti-static precautions, etc.

---

While "anti-static" precautions are a good practice its important to know that the Agnus is not a static sensitive device.

Quote:

---

Originally Posted by WhyreByter

Tried it again, and this time there's no screen at all. My TV says "No Signal", so I believe it's not just a black screen, but who knows when a 20+ year old machine is trying to talk to the new kid TV. :)

Tried it with/without the a501, different, known good PS, verified the a520 is working well (used it on a known good a1200). So, I'm not sure if I made a bad situation worse, or if it was just a goner to begin with. :(

---

Unfortuantely the system cannot lock a base address - hence the LED flashing.

This can happen with a bad GARY or Agnus - but in this case I think its because it has a a conflict on Address 19 and 20 (JP2)

Quote:

---

Originally Posted by WhyreByter

I'd like to get it working, and pass it along to someone who will use it (my a1200 suits me well, I just wanted to rescue this thing). Any suggestions on where to start troubleshooting it? My gut is "replace everything that's socketed", but I don't have a spare a500 to do that...

Thanks!
WhyreByter

---

Okay -

Firstly you need to cut the trace between 2 and 3 of JP2 - ensure that this is cut by using a multimeter in continuity mode

Ensure that all the pads of JP7A are also isolated from each other by again testing continuity between the pads

Here is a quick how to (click for images to Zoom)

Schematic
http://s2.postimage.org/1kt1shqjo/A500_6a_1_MBCHIP.png

JP2
http://s2.postimage.org/1kt53kfj8/jp2_zoom.jpg

JP7A
http://s2.postimage.org/1kt3g131g/jp7a_zoom.jpg

With the Rev6A you can populate the motherboard with 4x (256x4) -80ns Chips =D

remember, that by populating the motherboard you will be rendering the trapdoor unusable. To be fair modifying EXRAM (JP7A already does this anyway)

Good luck, hope this ramble helps =)

Thanks, Zetr0! While it didn't specifically solve my current issue, it does address one of my follow-on questions about what JP2 and JP7A are.

As to my current issue, I left out 2 important bits of info:

- JP2 is only connected on 1-2, not 2-3
- After I reseated all the chips, the power LED comes on steady, not pulsing anymore

@rkrauer: I just took a good, close look at the agnus socket. It has all its fingers, and a magnified view shows no fractures. Not saying that it's not bad, but a visual inspection doesn't reveal any anomolies.

Thoughts?

Thanks again for your help!

--WhyreByter

Im sure there will be some Amigans on here that wont like this suggestion.... :)

Throw it in the bin and buy another working a500 (or better still and a600 or a2000). This sounds harsh, sorry, but I have found out the hard way that you will spend hundreds of dollars of time and parts fixing a system that is literally worth nothing. A500s are the most worthless Amiga made - you can usually buy a good working example for $50.00 to $80.00.

It is simply not worth your time trying to fix it (unless it is something VERY simple and inexpensive).

A basic a600 can be had for $100.00 to $150.00 in vgc. Except for having to replace a few caps they have very good reliability as everything is surface mounted. They already have an internal ide, 2mb chip capable, have ecs as standard and at least ks 2.04.

Oh, and if you end up binning the a500, keep the psu - the only good thing about the a500 was its heavier duty psu which is compatible with (and much better than the standard psus of) the a1200 and a600.

Again, I hope this does not come across as being harsh as that is DEFINITELY not the intension, the suggestion is simply to save you losing hair, time and money on a pointless quest. To put it in perspective, would you spend 4 hours fixing a $50.00 vacuum cleaner?

Quote:

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Originally Posted by Zetr0

Hiyas WhyreByter

lets analyze =)

Quote:

---

Originally Posted by WhyreByter

I've got an a500 that doesn't want to wake up. Here's what it is, what I've done, and the symptoms:

---

okay lets lookie at what you have

Specs:
Rev 6a motherboard (good)
8372A fat agnus (good)
A501 in the trapdoor (okay)
JP2 shorted on the uppermost pads (pad 1 & 2 = good)
JP2 Pads 2 & 3 Cut (you need to do this)
JP7A open (good)
A520 video adapter (caution these can be flaky)

Quote:

---

Originally Posted by WhyreByter

When I first turned it on, it showed a green screen, a pulsing power LED, and no floppy activity. The intertubes suggested either bad Chip RAM, or a faulty Agnus, with reseating the Agnus as the possible fix. Tried it without the a501, and the same result.

---

This is the classic memory assertion failure - there is a base conflict of address.



While "anti-static" precautions are a good practice its important to know that the Agnus is not a static sensitive device.

Quote:

---

Originally Posted by WhyreByter

Tried it again, and this time there's no screen at all. My TV says "No Signal", so I believe it's not just a black screen, but who knows when a 20+ year old machine is trying to talk to the new kid TV. :)

Tried it with/without the a501, different, known good PS, verified the a520 is working well (used it on a known good a1200). So, I'm not sure if I made a bad situation worse, or if it was just a goner to begin with. :(

---

Unfortuantely the system cannot lock a base address - hence the LED flashing.

This can happen with a bad GARY or Agnus - but in this case I think its because it has a a conflict on Address 19 and 20 (JP2)

Quote:

---

Originally Posted by WhyreByter

I'd like to get it working, and pass it along to someone who will use it (my a1200 suits me well, I just wanted to rescue this thing). Any suggestions on where to start troubleshooting it? My gut is "replace everything that's socketed", but I don't have a spare a500 to do that...

Thanks!
WhyreByter

---

Okay -

Firstly you need to cut the trace between 2 and 3 of JP2 - ensure that this is cut by using a multimeter in continuity mode

Ensure that all the pads of JP7A are also isolated from each other by again testing continuity between the pads

Here is a quick how to (click for images to Zoom)

Schematic
http://s2.postimage.org/1kt1shqjo/A500_6a_1_MBCHIP.png

JP2
http://s2.postimage.org/1kt53kfj8/jp2_zoom.jpg

JP7A
http://s2.postimage.org/1kt3g131g/jp7a_zoom.jpg

With the Rev6A you can populate the motherboard with 4x (256x4) -80ns Chips =D

remember, that by populating the motherboard you will be rendering the trapdoor unusable. To be fair modifying EXRAM (JP7A already does this anyway)

Good luck, hope this ramble helps =)

---

Bloody hell, you really know your stuff Zetr0! :lol: :thumbsup:

Quote:

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Originally Posted by abraXXious

Im sure there will be some Amigans on here that wont like this suggestion.... :)

---

I hear you... I just got it today, along with a bunch of software from a guy who swore it was working (:bs:). My own fault for not checking it out, but I was in a hurry. I'm not too disappointed, I'm enjoying my a1200/1230/Indivision, and got the package as much for the software as anything.

But, it seriously looks well-kept. Give the case a light bath, and sort out the issues and it'd be almost like new. I just hate to toss it without spending a bit of time/effort on it.

--WhyreByter

@WhyreByter

hmmm, If you are positive that the traces are cut on both JP2 and JP7A then the I suspect the problem will probably lie with GARY, do you have another to test?

Its also important to mention that my good friend rkauer is also correct - it could be a CPU fault, since this unit was not tested before hackery.

Don't beat yourself up over it though, these things happen, GARY's and 68K motos are easy to come by and cheap enough (if not free) if you ask nicely =)


@AmiNeo

That's what happens when you stay up late, with insomnia and read technical manuals, schematics and hackers guides - y'know all the stuff ones mum typically warns you not to do..

hey... your up late/early

I threw out a rev 4 a2k mb only a week ago, he could have had the gary, 68k etc off it. :(