2 bombs at boot

[DaRyon]

Hello Exxos
I have a very strange issue,
1° all PSU caps are changed already, I know my PSU & my floppy, my Keypad are good (I exchanged them with another Atari)
2° When everything is connected on the mother board I always have 2 bombs at boot.
3° If I remove the keypad connector, the TOS boot correctly and Desktop is ok except don't detect the Floppy. (Bip Bip .... all time like of a key was press permanently...)
any idea of what to investigate further ?
thanks
David

[Steve]

Hello Exxos
I have a very strange issue,
1° all PSU caps are changed already, I know my PSU & my floppy, my Keypad are good (I exchanged them with another Atari)
2° When everything is connected on the mother board I always have 2 bombs at boot.
3° If I remove the keypad connector, the TOS boot correctly and Desktop is ok except don't detect the Floppy. (Bip Bip .... all time like of a key was press permanently...)
any idea of what to investigate further ?
thanks
David

If you check out these error codes:
https://www.atari-forum.com/viewtopic.php?t=15500

It seems 2 bombs means 'drive not ready'. I would probably focus on mandatory upgrades like: floppy drive pull-up resistors and the DMA pull-ups.

[JezC]

Just to rule out one possible issue, can you tell us which TOS version you are using?
IIRC TOS 2.x needs a floppy drive connected or it reports 2 bonds at boot anyway

[rubber_jonnie]

Hello Exxos
I have a very strange issue,
1° all PSU caps are changed already, I know my PSU & my floppy, my Keypad are good (I exchanged them with another Atari)
2° When everything is connected on the mother board I always have 2 bombs at boot.

Always a good start.

3° If I remove the keypad connector, the TOS boot correctly and Desktop is ok except don't detect the Floppy. (Bip Bip .... all time like of a key was press permanently...)
any idea of what to investigate further ?
thanks
David

Firstly, you really need to state what machine it is (ST, STF, STFM, STE etc) and what version of TOS so we know what we're dealing with. For example, if TOS 2.06 does not detect an FDD then it will bomb on startup. Usually that's with 4 bombs, so not quite the same, but worth knowing what you're dealing with.

Second, AFAIK with the keyboard removed, STs (Definitely Megas) will behave as though there is a key pressed, so don't worry about that, it just needs a keyboard. Check to be sure the connector cable is correctly oriented, and check both ends of the KBD cable for bad connections.

With regards to the FDD, is there any sign of life from it during boot at all? Is it the original FDD or have you swapped it for a PC drive? PC drives are normally set to ID1, but ST drives require an ID of 0.

I'd check that power is good, as I once had an STFM where the power wires for the FDD had freyed and the GND was touching 5v at the point it connected to the mainboard. You can check with a magnifying glass and multimeter in continuity mode to see if the wire is freyed and shorting.

Also check that the FDD is getting +5v at the plug. You can always double check that the +12V is also present, but it's only usually the older drives that need it. Check it anyway just in case.

Finally, check the FDD data cable is OK and not reversed. If you get a solid on FDD LED then it may be reversed.

[DaRyon]

Hi everyone

thanks a lot for all your feedback
so to answer your points:
I'm not sure about the TOS version since I can't manage to boot it (no desktop)
is there a way to know when the Atari is not booting properly ?
this is a 1040 STF version serial number A17BI4016960M original TOS

For you information, I tried to plug another floppy disk (which I know it works on another 520STE) same 2 bombs popping up

Going to try the pull up fixes ? looks the obvious one isn't?

Best
David

[olivier.jan]

As it’s a 1040 STF, unless you have a special add-on, the TOS version is < 2, so you can safely boot without floppy. What happens if you boot with the keyboard but without the floppy ?

[Smonson]

If you check out these error codes:
https://www.atari-forum.com/viewtopic.php?t=15500

2 bombs is Bus Error. That top list is the GEM error code numbers.

I see 2 bombs a lot because I suck at programming ;)

[Steve]

@Smonson AHH thanks I never noticed this :)

[DaRyon]

As it’s a 1040 STF, unless you have a special add-on, the TOS version is < 2, so you can safely boot without floppy. What happens if you boot with the keyboard but without the floppy ?

In this case the system is showing 2 bombs as well. look like the problem is coming from the keyboard connection / mother board because when I try with another keyboard (the one from my 520st that I know it works) I get same 2 bombs as well

[rubber_jonnie]

OK, so the current status is:

1. You get 2 bombs on boot if the keyboard is connected.
2. If you connect a known working keyboard you get 2 bombs.
3. Booting with no keyboard gets you to the desktop, but you get a beeping noise like keypresses are being made and no floppy.

So does the spare 520 work with the keyboard from the 1040? I can't see that you tested it, but if it does work it rules out the keyboard. You should of course test the keyboard for shorts and the like before doing this.

I do know if the keyboard is disconnected on the Megas, it will beep continuously like a key is being pressed. I haven't tried with the ST but I expect the result is the same.

You should also reseat any socketed IC's and clean the contacts with IPA then use something like Electrolube or Deoxit before putting the IC's back in.

The schematic shows (Well as best as I can tell for an STF) that U54 is the 6850 used for the keyboard. That's likely soldered in but it may be an issue, but clean the IC contacts first for everything else.

If you don't have a PLCC IC puller I'd suggest getting one, they are quite inexpensive and do prevent damage to the custom IC's. Make sure you make a note of the IC orientation too, take photos if needed as inserting incorrectly can kill the IC's.