Amiga 500 hangs at floppy boot(loader)

[Turrican_3]

Hi guys, this thing is driving me crazy so I hope someone can help.

Amiga 500 rev 6A, board at first glance seems in good shape.

System is able to boot kickstart (1.3) and shows the familiar hand, floppy clicks as usual waiting for the disk, but when I insert one it seems to load the bootsector and then hangs with a white screen. The drive keep spinning, for the record.

Tried with both a known working Gotek (this is how I noticed it goes to track 0, I have the OLED modded one) and physical floppy disk drive.

I also swapped every socketed IC (including Fat Agnus), one at a time (excluding CIAs that I tried simultaneously) with the ones of another A500 rev. 6A I own. By the way I also had a look at dozens of threads on this very forum but I don't think I've found this exact issue yet.

Any ideas what to check next? I'm stuck now. :-\

[Turrican_3]

I don't know if this is related and/or helps with diagnosing the problem, but I've just noticed this Amiga has issues with a 512K espansion (guru) at power on.

The very same expansion works flawlessly on the other rev 6A motherboard.

I also have reason to believe this Amiga has been serviced in the past, since accessing the bottom side of the motherboard I can see some dirty areas around certain components (possibly not properly cleaned after rework? - two RAM chips for example are socketed and from a different manufacturer than the others) and I also suspect a couple of capacitors might have leaked, but those seem to be related to video output judging from schematics - I'm talking about the two big ones on the upper left part of the motherboard, near the RGB port; at least one of them seems bad (brown stuff at its bottom)

[lesta_smsc]

Any chance the expansion port has some bent pins that are making contact? I had strange errors after a pin connection.

[Turrican_3]

Apparently no such thing, I guess it's something else. :-\

[R4M]

I had a similar problem with a gotek connected as df0: with a broken cable. Are you sure that the bootblock is loaded? Maybe the track0 signal is not working and the OS steps the head indefinitely.

[Turrican_3]

Please note I only have a basic understanding of electronics and the Amiga inner workings.

Having said that, the OLED display of the Gotek drive says 01.00 first, then 00.00 if I'm not mistaken. After that, screen stays white and nothing else happens.

Cables should be ok since the same drive + cables combo works on a different Amiga, so I guess if what you mention is the actual issue there must be something wrong that should be somewhere starting from the motherboard floppy connector going onwards, right?

[solarmon]

I assume you are talking about the internal floppy drive. Have you tried with an external floppy drive connected to the external floppy drive connector?

It sounds like possibly some of the floppy connector traces are broken?

Take some closeup pictures of the floppy connector and surrounding areas and post it here so that we can see, and maybe somebody can spot something.

A good resource to help troubleshooting is http://www.amigapcb.org/, and with a multimeter you can use this to check that traces are working or not.

[Turrican_3]

Originally Posted by solarmon

I assume you are talking about the internal floppy drive. Have you tried with an external floppy drive connected to the external floppy drive connector?

Yeah sorry, it's DF0: I'm talking about.

Unfortunately my 2.05 A600 ROM doesn't seem to properly work when inserted (I thought they were interchangeable at least for basic functionality, guess not? or maybe it's a further hint at something being wrong) so with this A500 only having Kickstart 1.3 available, booting from an external drive is out of the question.

Take some closeup pictures of the floppy connector and surrounding areas and post it here so that we can see, and maybe somebody can spot something.

You are right, will definitely do as soon as I come back home!

[solarmon]

And with Kickstart 1.3 ROMs you won't also have the benefit of the early boot up screen that shows what disk drives are detected.

But definitely nice clear close up pictures will help us help you!

[Turrican_3]

Uploaded photos to imgur to preserve maximum detail/resolution

https://imgur.com/Mn6jJGl.jpg (motherboard top)
https://imgur.com/DNnBw1E.jpg (motherboard bottom)
https://imgur.com/xFkjqHH.jpg (CIA B area detail)
https://imgur.com/6vyxHEX.jpg (CIA A area detail)

https://imgur.com/pveSD0c.jpg (leaked capacitor(s?))
https://imgur.com/aNIEBAQ.jpg (possibly reworked RAM)
https://imgur.com/fFW5Ihz.jpg (CIA A bottom side area)
https://imgur.com/YKQ4MQ2.jpg (internal expansion area)

(full album --> https://imgur.com/a/rAdfT7A)

I also checked continuity between floppy connector and CIAs/Paula/Gary, everything seems ok according to schematics, EXCEPT the connection(s) to the 74LS38 that I will test later today (seems to be major difference between rev 6A and 8A, used the latter as a reference for practical reasons but please feel free to correct me if I'm wrong!)


EDIT damn I didn't notice bottom motherboard is not properly focused! :-\
I can take another shot if needed for troubleshooting (here's hoping zoomed photos are enough)

[solarmon]

There seems to be corrosion on the internal expansion connector pins (to the right of the picture) - these are the power and ground pins, I believe. So that might explain your memory expansion board issues.

[demolition]

Originally Posted by Turrican_3

Unfortunately my 2.05 A600 ROM doesn't seem to properly work when inserted (I thought they were interchangeable at least for basic functionality, guess not? or maybe it's a further hint at something being wrong) so with this A500 only having Kickstart 1.3 available, booting from an external drive is out of the question.

KS 2.05 should work fine in any Rev 6 A500.

[Turrican_3]

Originally Posted by solarmon

There seems to be corrosion on the internal expansion connector pins (to the right of the picture) - these are the power and ground pins, I believe. So that might explain your memory expansion board issues.

Yes, right now I've decided to avoid connecting the expansion and just focus all efforts on the boot issues first, hopefully I can take care of that later.

[Turrican_3]

Originally Posted by demolition

KS 2.05 should work fine in any Rev 6 A500.

Hmm that's not good to hear. :-\

This 2.05 comes from an A600 that I purchased second hand, I only discovered upon further ispection it was actually an EPROM. But since it is working properly on the A600 it shouldn't make a difference on the A500 if, as you said, they are actually compatible.

I also have a proper original A600 ROM (not 2.05, but it's not relevant), maybe I can try that one instead?

[solarmon]

Have you tried swapping/switching the CIA chips (which are the same) to see if you get the same or different behaviour?

[demolition]

Originally Posted by Turrican_3

I also have a proper original A600 ROM (not 2.05, but it's not relevant), maybe I can try that one instead?

Sure, the other one could be faulty somehow (unless it works in the 600).
I think 2.05 does more hardware checks so that could also be why it fails to get to the KS screen. What is the color of the screen when it stops changing? If it changes from black, then I think it passed the ROM checksum which means that it is not faulty.

[Turrican_3]

Originally Posted by demolition

Sure, the other one could be faulty somehow (unless it works in the 600).

Hmm no, it actually works on the A600. I think I will try both the ROM and the EPROM (again), so that I can report back on the screen color too. :-)

(PS: I made a mistake before, I meant "not 37.350", i.e. for the A600 I currently have a 37.300 ROM and a 37.350 EPROM, both working in their original hosting computer)

Originally Posted by solarmon

Have you tried swapping/switching the CIA chips (which are the same) to see if you get the same or different behaviour?

Yep, also tried a completely different set from the working A500.

I haven't tried replacing every IC *simultaneously* yet though.

[Turrican_3]

Tried again the A600 37.350 EPROM, I can confirm it does not work in this Amiga 500, screen goes black at power on, then 1-2 shades of grey I think, then white, after that power LED starts blinking (slowly, like a Guru meditation, but no such message ever shows on screen), then again black/grey/etc. while the LED keeps blinking.

I'm going to try the 37.300 official ROM now and will report back.

[Turrican_3]

Ok this is getting more and more interesting (or weird/complex?)

I've tried the 37.350 EPROM on the other A500 (same motherboard revision) and it works indeed!

So, to recap, for some reason this A500:

- can complete the Kickstart 1.3 loading (shows hand and floppy clicks)
- cannot complete the Kickstart 2.0x loading (enters some pseudo-guru loop)
- with Kick 1.3 hangs at floppy bootloading
- doesn't seem to accept a 512K internal expansion (guru)

[demolition]

I guess memory corruption could cause this kind of behaviour. The KS ROM doesn't do a proper test of all the memory but only a few select addresses to identify available memory. The guru is probably a result of the CPU trying to execute some invalid opcode which triggers the exception handler.

It would be useful to put a DiagROM in it and see what it says, but I don't suppose you have a suitable EEPROM and a burner handy?