Amiga 600 Boot Problem

[Gary335]

So I recently purchased an Amiga 600 (US) on Ebay, and am having some trouble getting it to boot. When I power it on, it goes to a yellow screen, which flashes red every few seconds. I also noticed that the power light on the system flashes constantly, and the Caps Lock light flashes each time the screen flashes red.

Can anybody tell me what this indicates? My understanding is that the yellow indicates a CPU problem, but the red flash is throwing me off. Any help anyone could provide would be greatly appreciated!

[Oldsmobile_Mike]

Have you already done all the obvious stuff? Removed any expansions, reseated the ROM chip, inspected the capacitors, etc.?

[Gary335]

Have you already done all the obvious stuff? Removed any expansions, reseated the ROM chip, inspected the capacitors, etc.?

Yes. There are no expansions, but I did reseat the ROM chip, and also tried a different ROM chip (the one that was in the system was an older version, the one I want to use is a 3.1 ROM). Capacitors all look good, in fact the whole system looks just beautiful for it's age.

[Pat the Cat]

Yes. There are no expansions, but I did reseat the ROM chip, and also tried a different ROM chip (the one that was in the system was an older version, the one I want to use is a 3.1 ROM). Capacitors all look good, in fact the whole system looks just beautiful for it's age.

Flashing red is usually a sympton of a bad onboard memory chip, as I recall. Certainly some kind of hardware issue with exec not starting up properly... so the processor and ROM are probably good.

If you've opened it up already, try disconnecting the floppy drive at either end - could be that that's up the creek. Same with a hard disk.

I guess in theory a bad keyboard MIGHT do it, but on the A600 the keyboard is just a set of switches on a VERY fiddly cable. Probably no need to unplug it, if a switch is bad, it doesn't stop a boot from happening. So leave that alone, for the time being.

Could also be a loose screw, washer or similar, jammed on the board and causing a short. Unscrew the board from out of the case and check. Be careful, the connectors on the back also have little threaded screw headers that also need to come out to examine the board's backside. You need a hexagonal shaped tool or spanner (wrench over the pond) ideally, but pliers will do the job, they just cause scratches.

EDIT: Oh yeah, ROMs. The 3.1 version has to specifically be for an A600. They are not very swappable between Amigas, as a rule of thumb.

[Gary335]

Flashing red is usually a sympton of a bad onboard memory chip, as I recall. Certainly some kind of hardware issue with exec not starting up properly... so the processor and ROM are probably good.

If you've opened it up already, try disconnecting the floppy drive at either end - could be that that's up the creek. Same with a hard disk.

I guess in theory a bad keyboard MIGHT do it, but on the A600 the keyboard is just a set of switches on a VERY fiddly cable. Probably no need to unplug it, if a switch is bad, it doesn't stop a boot from happening. So leave that alone, for the time being.

Could also be a loose screw, washer or similar, jammed on the board and causing a short. Unscrew the board from out of the case and check. Be careful, the connectors on the back also have little threaded screw headers that also need to come out to examine the board's backside. You need a hexagonal shaped tool or spanner (wrench over the pond) ideally, but pliers will do the job, they just cause scratches.

EDIT: Oh yeah, ROMs. The 3.1 version has to specifically be for an A600. They are not very swappable between Amigas, as a rule of thumb.

Just tried booting without the floppy or keyboard plugged in and I get a green screen for about 3 seconds, then it goes to the yellow with flashing red.

Have not yet taken the board completely out of the case to check on screws, washers, etc. Will take that step next. The ROM chip is for the 600. I originally purchased it for a UK 600 I also have.

[Pat the Cat]

Just tried booting without the floppy or keyboard plugged in and I get a green screen for about 3 seconds, then it goes to the yellow with flashing red.

Have not yet taken the board completely out of the case to check on screws, washers, etc. Will take that step next. The ROM chip is for the 600. I originally purchased it for a UK 600 I also have.

Oh dear. Don't try turning it on again until you've checked everything over visually for something nasty. Like a burst capacitor, or a little bit of metal causing a short cirtcuit.

http://wiki.classicamiga.com/Amiga_boot_error_code_colours

Could theoretically be the power supply, too, I guess. Check the voltages it's giving out with a multimeter.

But, could be just the old ROM is dead and the new one works fine.

http://www.hardwarebook.info/Amiga_500/600/1200_Power_Supply

[Gary335]

Oh dear. Don't try turning it on again until you've checked everything over visually for something nasty. Like a burst capacitor, or a little bit of metal causing a short cirtcuit.

http://wiki.classicamiga.com/Amiga_boot_error_code_colours

Could theoretically be the power supply, too, I guess. Check the voltages it's giving out with a multimeter.

But, could be just the old ROM is dead and the new one works fine.

http://www.hardwarebook.info/Amiga_500/600/1200_Power_Supply

Checked everything over, nothing seems amiss. Capacitors are fine, everything looks fine. Can't see anything that might be causing a problem. Tried another power supply, same result. So I'm thinking we can rule that out.

[Castellen]

Flashing red is usually a sympton of a bad onboard memory chip, as I recall. Certainly some kind of hardware issue with exec not starting up properly... so the processor and ROM are probably good.

I guess in theory a bad keyboard MIGHT do it, but on the A600 the keyboard is just a set of switches on a VERY fiddly cable. Probably no need to unplug it, if a switch is bad, it doesn't stop a boot from happening. So leave that alone, for the time being.

EDIT: Oh yeah, ROMs. The 3.1 version has to specifically be for an A600. They are not very swappable between Amigas, as a rule of thumb.

Red indicates a ROM checksum failure.  One of the first things the system does on power up is build a checksum of the entire ROM and compares it to the checksum stored in ROM.  If they're different, it throws a red screen.  The ROM is usually something that generally works fine or not at all, so most of the time if you have an actual ROM issue, the CPU will end up executing garbage right away, then fail within the first few instructions to the point you'll only ever see a black screen.

Therefore most of the time when you see a red screen, it's often something screwing with the CPU data bus causing the checksum calculation to be wrong.


Agreed, a keyboard fault won't cause this problem.


The 16-bit ROMs are exchangeable between A500, A2000 and A600.


Most of the symptoms so far point to a chip memory problem.  Despite popular belief, the power up memory test (which makes the green screen) is not very thorough.  It's kept brief in order to keep boot times practically short.

What happens during boot in terms of memory is essentially:
- Write exception vector table (46 words) to bottom of memory
- Read them all back, if any aren't as expected then do a green screen
- Do a single word write+read test of chip memory every 16k, if there's a failure in the first 256(?)k then do a green screen
- Set up exec in chip memory - if something breaks here due to bad memory which wasn't detected in the previous test, you'll usually get a yellow screen (exception error)


I'd suggest replacing either/both DRAM ICs in the A600 and see if that fixes the problem.  As I recall, the system should boot normally without U17 fitted, but U16 always needs to be present and working correctly.  Failing that look at the 16 CPU data bus lines with an oscilloscope and see if any lines don't have a clean 0-5Vp-p waveform.  Could also be a CIA fault, both 8520s live on the CPU data bus and people plugging stupid things into the Centronics port can often damge U7, which can then proceed to mess up the data bus and cause similar symptoms as described here.

[Pat the Cat]

I'd try the new ROM anyway. Take care prising the old one out - small flat bladed screwdriver is good enough, make sure you get the notch the right way around. You have to do each end, in turn, a bit at a time. Don't lever it out all the way at once, the pins get bent all ways.

If the old ROM is corrupted and isn't carrying out boot properly, that would also explain the behaviour, to a certain extent. Unikely, but worth a try with the new one. ROM chips are pretty robust, as components go. But when the PROM type are dead, they're dead, AFAIK.

...Could also be a CIA fault, both 8520s live on  the CPU data bus and people plugging stupid things into the Centronics  port can often damge U7, which can then proceed to mess up the data bus  and cause similar symptoms as described here.

Gold dust knowledge, thanks.

It's  a bi-directional port but it's very limited compared to where parallel  ports went. I never knew the data bus could be damaged by silly connections but  it's very easy to plug the wrong thing in there.

[Gary335]

The ROM makes no difference. The result is the same with either one. How would one go about replacing U16 and 17? These appear to be soldered directly to the board. Also, where would I obtain these replacement parts? I imagine I'd have to order them from somewhere on the other side of the pond since I'm in the US?

[Pat the Cat]

The ROM makes no difference. The result is the same with either one. How would one go about replacing U16 and 17? These appear to be soldered directly to the board. Also, where would I obtain these replacement parts? I imagine I'd have to order them from somewhere on the other side of the pond since I'm in the US?

Pretty much everything on the A600 is soldered apart from the ROM. ROHS standards came in 1992. Lead free solder, so count your blessings that fixing it isn't going to cause health damage.

Spare parts you are looking for are an 8520 (CIA, Complex Interface Adaptor) in PLCC or is it FPGA form (? square SMD) for U7, and if that doesn't work, the RAM chip or Chips. I don't know that off the top of my head, but it's written on the chips.

You may or may not be able to get spare parts. From anywhere. But, they're generally to be had, if you look hard enough and are patient.

As for the soldering skills, if you don't have, find someone local that does. Makerspace or Hackerspace close to you? Fablab, anything like that? Worth a search engine check on your location.

Solder containing lead is now pretty rare, but still available. No more is going to be produced though - at least, not in the USA, Europe, or Japan.I think China has severely restricted the use of lead, but the Chinese economy is so huge, it's very difficult to be sure that environmental monitoring is checking up on that, as far as solder goes.

[Castellen]

How would one go about replacing U16 and 17? These appear to be soldered directly to the board. Also, where would I obtain these replacement parts?

The original DRAM is a Hitachi HM514260 which are usually easy to find on popular auction sites.  Be sure to get the SOJ package (JP suffix on the part number), so specifically you'll need the HM514260JP-8 or -7 for the right package with either 80 or 70nSec timing.

And obviously it's surface mount soldered, so a couple of minutes work for someone with a rework station.


Likewise, the 8520s are both PLCC44 packages, which can be found on the second hand market.  I've even got a bunch in stock.

It's  a bi-directional port but it's very limited compared to where parallel ports went. I never knew the data bus could be damaged by silly connections but  it's very easy to plug the wrong thing in there.

 


It met the design requirement of meeting the Centronics standard at the time and generally worked fine.  Unfortunately there was little protection on the I/O lines, which are handled directly by both 8520s, and lots of things happen to use 25-pin D-range connectors.  So you ended up with people jamming any random 25-way connector into the port which could do varying degrees of damage.  Worst case it would damage U7 or U8 to the point where they'd interfere with the CPU data/address busses, then you'd have no booting, or you'd have memory test failures, etc.

The serial port is a lot more tolerant as the 1488/1489 RS232 line drivers offer reasonable protection to the 5V I/O.

Pretty much everything on the A600 is soldered apart from the ROM. ROHS standards came in 1992. Lead free solder, so count your blessings that fixing it isn't going to cause health damage.

These machines were all built with standard 60/40 tin/lead solder.  Though unless you mistake it for a pork chop and start eating it, or go huffing the lead fumes for years, a one-off repair job such as this is very unlikely to pose a health issue.

[Pat the Cat]

...These machines were all built with standard 60/40 tin/lead solder.  Though unless you mistake it for a pork chop and start eating it, or go huffing the lead fumes for years, a one-off repair job such as this is very unlikely to pose a health issue.

That could be why some people with access to tools and have skills are leery about doing the work?

But thanks, always seemed to need higher temp to me. Less tolerant than lead solder.

Guess I didn't take an iron to an SMD Amiga that often. Didn't need to.

But then, I was taught to be careful when connecting and disconnecting things.