A1200 black screen and buzzing from floppy

[Retroplay]

Ok, here's the story;

I was dumping Deep Core using the CAPS dump disk on A1200 rev1.D4, like I have done before successfully with other games (always only 81 tracks).
In the middle of dumping disk 2 (disk 3 dumped ok) it halted and stopped at a gray screen, after a little while a buzzing sound came from the floppy drive (AmigaKit drive), still stuck on the gray screen.
I turned off A1200 and left it off for 20-30 secs only to be greeted by a black screen when I turned it back on.

I disassembled the Amiga and removed HDD and ACA1232, turned it on again and floppy drive went berserk and still nothing but a black screen.

The floppy drive, ACA1232 and Kickstart 3.1 roms work fine in my other A1200, which also is a rev 1.D4.

So anybody got an idea what has blown up here ?

[kipper2k]

Did you remove the floppy drive and try rebooting? That appears to be main suspect at the moment. (although you say it works in other, still try.

An Amiga stuck on a grey screen when booting indicates a bad U8 (for the A1200) which is the even CIA which controls the floppy functions.

[Retroplay]

I have even tried a different drive I know works, nothing.

[edit]
As soon as I power on the 1200 the floppy led goes ballistic with or without drive connected and drive makes a very "unhealthy" noise when connected.

And as I previously said, it just stays at a black screen.

[kipper2k]

Originally Posted by Retroplay

I have even tried a different drive I know works, nothing.

[edit]
As soon as I power on the 1200 the floppy led goes ballistic with or without drive connected and drive makes a very "unhealthy" noise when connected.

And as I previously said, it just stays at a black screen.

Black screen at boot normally indicates that the CPU did not initialize. did something metallic drop through the casing onto the board. If the floppy LED is doing weird things then it is still possibly caused by the CIA chip.

[Retroplay]

My bet is CIA then as nothing has been dropped on the board.

Are there any places which offers repairs for this as I'd really like to get it going again.

[Turran]

Send a PM to TomCrazy =) Thats in Sweden. Not too far off.

[prowler]

Have you checked the A1200 with another PSU, or tried the PSU with another machine?

[Retroplay]

Yes, I have my spare rev 1.D4 A1200 up and running using the same A500 PSU.

After a quick timing fix the ACA1232 was stable too.

@Turran
Thanks I'll do that.
Is this him btw ?
http://www.youtube.com/user/RetroGameModz

[roy bates]

yes thats tom

[TomCrazy]

Originally Posted by Retroplay

I have even tried a different drive I know works, nothing.

As soon as I power on the 1200 the floppy led goes ballistic with or without drive connected and drive makes a very "unhealthy" noise when connected.

And as I previously said, it just stays at a black screen.

I think I know exactly what kind of sound your floppy drive is making. It's from the spindle motor of the floppy drive turning off and on very quickly.

There is obviously something wrong with the motherboard and not the floppy drive.

The reason you're getting these symptoms is because you have a fault that is generating a sporadic behavior of the _MTR0 signal.

The _MTR0 signal is what controls the state of the spindle motor of the internal floppy disk drive (on or off). This signal is also driving the base of a PNP transistor that is in turn driving the floppy LED.
Sporadic blinking of the floppy LED means that there is something wrong with the signal that is driving this LED, which is the _MTR0 signal.
A problem with this PNP transistor is not very likely, since the floppy drive produced an "unhealthy" sound while the floppy LED was blinking. This suggests that the driving component for the PNP transistor is already at fault (that is, the _MTR0 signal).

The _MTR signal is being generated in the even CIA chip at U8.
It's then going into Gayle (U5) and coming out as _MTR0, which is the signal controlling the spindle motor of DF0 and the state of the LED for the internal floppy drive.

This kind of failure very much suggests that there is a chip failure, since the _MTR0 signal is changing state sporadically as soon as the motherboard is being powered up.
However, it doesn't necessarily mean that there is something wrong with the even CIA. It could just as well be something wrong with Gayle.

There should be an easy way to test this;

Gayle is the chip that is generating the _MTR0 signal out of the _MTR signal and _SEL0 signal. It probably does this by applying an OR-function to the _MTR and _SEL0, which results in _MTR0.
However, this MTR0 is only controlling the spindle motor of the internal floppy drive. The signal that is controlling the spindle motor of the external floppy drives is called _MTRX, and this _MTRX signal is not being generated in Gayle, but in some other logic gates at position U26.

What this means is that if there is something wrong with the even CIA, that fault will propagate through both Gayle and the gates at U26, causing this erratic floppy behavior both on the internal disk drive and the external floppy disk drive.
However, if there is something wrong with Gayle, the sporatic floppy behavior will only happen on the internal floppy drive and not on external floppy drives.

I don't think there is any point in sending the motherboard to me or anyone else at this stage. First of all, I think you should try to connect an external floppy disk drive to the motherboard and switch on the power. You can leave the internal floppy drive disconnected during this test. In fact, it's better to leave the internal floppy drive disconnected, because it will be easier to hear any possible erratic sounds coming out from DF1 if DF0 is disconnected, since we already know that DF0 is making a lot of noise.

So to start with, connect an external floppy drive while having the internal floppy drive disconnected. Then turn on the power.
Let me know here what the outcome of that test was.

Since we can already rule out a power supply problem, I think it's very likely that there is something wrong with either one of these two chips. I don't have either of these two chips as spare parts at home. Since the test I've explained about here is very simple, I think it's better that you try to perform the test by your own to start with. Then you could possible try to check the possibilities of finding a new chip or a donor for the needed chip before even sending the motherboard here.

But unfortunately, the test I mentioned is not bulletproof, since a sporatic change in the _MTR signal at the even CIA probably won't trigger an erratic behavior of the external drives if _SEL1 is not changing states sporatically as well.

There are also a few other things that complicates the situation a bit.
The CPU address bus has 4 bits hooked up to both the CPU, Alice and the even CIA.
The CPU data bus has 8 bits going to both the CPU, Gayle and the even CIA.

This means that it's impossible to completely verify what chip is at fault without futher testing. It might not even be the even CIA that is at fault. There might be something else that is controlling the even CIA that is faulty, causing the even CIA to act erratically. Gayle and the CPU is what comes to mind. (In this case, it would be a different problem with Gayle than the one I was first talking about.)

Let me know the result of hooking up an external floppy drive to the motherboard and we'll take it from there.

[Retroplay]

I'll need to get an external drive then, once I've done that I'll report back.

[Retroplay]

Okay I got an external drive.

The drive works as I have tested it on my A500 successfully.

The A1200 however doesn't recognize it.

Here's what happens:
[ Show youtube player ]

Black screen, DF0 acting up and DF1 not working at all.