A500 Won't Recognize 3.1 ROM

[jammarob]

Continuity checks ok.

I'm stumped.

At this point I think i'll just pick up another A500

[ElPolloDiabl]

Check here. I'm sure the error code is in one of those old books.

http://www.bombjack.org/commodore/amiga-books.htm

Other than that, someone has gotten that error code after their battery leaked.

[orange]

if not mentioned already in thread, you might need to add missing resistor pack, iirc its near CPU.

[Faerytale]

U forgot to install Microsoft Plug & Play drivers!

[paul1981]

Is it different jumbled characters each time?

[DutchinUSA]

Orange, you talking about the following?: (forgot who wrote it but I cut & pasted it into an email to myself).

I had burned an EPROM (AMD AM27C400) with Kickstart 3.1 image for my A500+ but when I replaced the original ROM I got a red screen with flashing power LED. Very similar situation to the one described by orange.

The kickstart was the 40.063 version intended for A500/A600/A2000. I had verified the CRC-32 checksum before burning it. The image wasn't corrupted or modified. I had checked it with the SKick. Everything had worked fine.

With the CPU replaced by the turbo board (030 CPU) the kickstart booted correctly (I'm sure it wasn't a 020+ image because it had been soft-kicked earlier and had worked with the stock 68000 CPU, the EPROM was also verified if it contained the programmed data).

Strangely when my Action Replay III card was connected the kickstart booted correctly but required disabling of the cartridge (actually it was A2000 version of the Action Replay III connected through a bus board). I have burned another EPROM with the same data but the story repeats.

Then I started to suspect that something strange must be happening on the CPU bus. I noticed that the Action Replay card had pull-down resistros on the data bus but my rev 8A motherboard was missing data bus pull-ups. I populated the missing resistor packs (RP108 and RP110) but nothing happened. I tried both pull up and pull down configurations without success.

Then I started to measure signals at the CPU socket with my scope and found out that when I touched with a probe some low order address lines the power LED flashing stopped. The system hung. It was deterministic behaviour.

I realized that also low order address lines (A16-A1) were missing their pull-up resistor packs (RP106 and RP107) so I removed data lines pull-ups and moved them to low order address lines. Since that moment everything works flawlessly.

You can locate aforementioned missing resistor packs next to the CPU socket on the A500+ rev 8A motherboard.

I don't really know why it initially worked with the original mask ROM but didn't with the CMOS EPROM. One possible explanation is an input leakage current of the ROM/EPROM chip. The 68000 CPU was manufactured using NMOS technology with relatively weak sourcing current of high output state (0.4mA). According to the datasheet of the ROM chip its input leakage current is ten times larger than the one of the EPROM.

I hope someone will find my description helpful.

just to see if i understood this. you installed two resistor packs at RP106 and RP107 to make the "AMD AM27C400" eprom working. what are the types/specs of these resistor packs?

Yes, I installed two resistor packs (aka resistor networks or resistor ladders) as specified in the rev 8A schematics: 9 x 4k7 in SIP-10 package.

One of the suitable components is BOURNS 4610X-101-472LF. You can buy them at Farnell.

[Oldsmobile_Mike]

^^^  That is some danged amazing troubleshooting, there.  Not sure if Rev 8A is comparable to his Rev. 5, but couldn't hurt to inspect if those components exist.  You sir, win the dancing banana award for the day!  :banana:

[DutchinUSA]

That wasn't mine though and it was in reference to a burnt kickstart.

I have heard what Mechy mentioned before though .. certain rom speeds will be fine in one machine but will be too slow in another (same model and everything) .. weird but true

[jammarob]

That is very helpful, thanks for that!

I'll get a hold of a logic probe and oscillator this weekend and start poking around the CPU.

It's certainly possible that one of these resistor packs could be faulty.

[jammarob]

**UPDATE**

I couldn't figure out this revision 5 A500, so I picked up a revision 6A A500 from a local electronics junk store today.

None of the 10-pin resistor packs mentioned earlier are populated on this board. It would NOT recognize the 3.1 kickstart EPROM until I populated RP107 with a 9 x 47K resistor pack.

It now recognizes the kickstart and boots, but adding an A508IDE causes it to become unstable.

Does anyone have the values for RP106, RP108, RP110 on a revision 6A?

[Oldsmobile_Mike]

I couldn't figure out this revision 5 A500, so I picked up a revision 6A A500 from a local electronics junk store today.

I'm impressed that they have "local electronics junk stores" in Texas that have Amiga parts!!!

I've got tickets to a tech event down there in Austin in September, anyplace you can recommend?

...btw, ripping my A500 apart in a few weeks for some upgrades.  It's a 6A, if you can't find those values before then I might be able to get them for you.  Not anxious about removing my VXL*30 though, haha.  

[jammarob]

Yep! Unfortunately, they are about to permanently close. Everything is 80% off, so the A500 was pretty cheap.

https://www.youtube.com/watch?v=AIy__NX9SvQ

[mechy]

I'm impressed that they have "local electronics junk stores" in Texas that have Amiga parts!!!

I've got tickets to a tech event down there in Austin in September, anyplace you can recommend?

...btw, ripping my A500 apart in a few weeks for some upgrades.  It's a 6A, if you can't find those values before then I might be able to get them for you.  Not anxious about removing my VXL*30 though, haha.  

Lol, i am jealous, i am in texas and our junk stores have nothing amiga ever ;/
 I am in a small town though

[mechy]

That is very helpful, thanks for that!

I'll get a hold of a logic probe and oscillator this weekend and start poking around the CPU.

It's certainly possible that one of these resistor packs could be faulty.

when you burned the eprom,did you fill it completely, i.e. concatenate it to double it them burn it to the full 4mbit eprom... hope that makes sense?

if not,then iirc it may address the empty half or some such and not work.

[paul1981]

Yep! Unfortunately, they are about to permanently close. Everything is 80% off, so the A500 was pretty cheap.

https://www.youtube.com/watch?v=AIy__NX9SvQ

Wow!

[danbeaver]

Since this is still an Amigakit ROM (and we are on an Amigakit web site), do you really want to not involve them in an issue that really is in the realm of customer support?

I only point this out as this thread is heading towards its third page...