A1200 Fault Speculation

[CDTV1991]

UPDATE: After solving the initial problem, the theme of this thread has now become "Project "Trigger's Broom" and follows the many repairs and replacements of my A1200.

I took a punt on a broken A1200 from eBay for a tenner. It hasn't arrived yet.

Seller wrote "Faulty amiga 1200 for sale, turns on but there is no display on the tv, tested rf and phono. might be an easy fix for someone? I did check motherboard but it does not look damaged and capacitors dont seem buldged? The rest is untested due to not being able to get it working. so is sold as non working for parts only"

Can anyone speculate what this fault could be?

I'll post an update when it arrives and I have a poke around.

It does not come with a power supply, but I have an A500 supply, will it work?

[prowler]

The video might still work from the monitor output. You will be able to test this if you have a TV with a SCART input and Amiga RGB to SCART lead.

If not, I can lend you an A520 modulator, which provides an RF and composite video signal from the Amiga's RGB monitor port.

If it works and you're happy with that, then I could sell it to you for a small fee. If not, or it doesn't work, then just return it to me.

[CDTV1991]

Originally Posted by prowler

The video might still work from the monitor output. You will be able to test this if you have a TV with a SCART input and Amiga RGB to SCART lead.

If not, I can lend you an A520 modulator, which provides an RF and composite video signal from the Amiga's RGB monitor port.

If it works and you're happy with that, then I could sell it to you for a small fee. If not, or it doesn't work, then just return it to me.

I've got a SCART lead to my TV for my CDTV set up, so i'll test it with that.

I've also got an A520 from an A500 in the loft

Will the A500 power supply work with the A1200?

[prowler]

Originally Posted by CDTV1991

I've got a SCART lead to my TV for my CDTV set up, so i'll test it with that.

I've also got an A520 from an A500 in the loft.

You're all set then.

Originally Posted by CDTV1991

Will the A500 power supply work with the A1200?

Yes. In fact, most A500 PSUs are better than those supplied with A1200s.

Good luck!

[orange]

i'd ask the seller if floppy drive 'clicks' or if there is hdd activity.

[CDTV1991]

Well, it has arrived

It doesn't work, although I expected it to be faulty (sold as faulty) and I'm interested in trying to diagnosing the fault and fixing it.

This is what I have learned so far. Let me know if you have any ideas on the cause of the fault or anything else I could try to test.

1. I plugged my working A500 PSU into the A1200
2. The green power light comes on
3. The caps lock light flashes briefly, but doesn't work after that
4. No FDD click

Plugged it into my TV via:

1. RF Out to TV - nothing
2. Composite Out to TV - nothing
3. A520 modulator RF Out (from my A500) - nothing
4. A520 modulator Composite Out - nothing
5. RGB Out via SCART lead - nothing

Each time the TV "thinks" there is a signal there and the screen goes black / dark grey.

Doing the same with my working A500 gives a picture every time, every option.

I opened it up and found:

1. A clean looking motherboard
2. No bulging capacitors
3. A slightly messy looking board for the internal RF modulator (link to photo below)
4. No loose cable connections

http://i299.photobucket.com/albums/m...a1200rfmod.jpg

Also noticed:

- An empty HDD holder
- Some missing screws
- Loose FDD drive
- Sticker on the keyboard (underneath the front casing) saying "Angel Software STOCK"
- Old silver warranty sticker with a hole through it, a non CBM (smaller white) sticker on top of that and then a "new" silver CBM warranty sticker on top of that. Seems odd because the seller had told be that there were no bulging capacitors, so he must have opened it up.

[johnim]

try reseating the roms and try again but notice which rom from which socket and the end pin holes left see here

http://www.ianstedman.co.uk/Amiga/am...0moboR118.jpeg

[orange]

perhaps you should measure voltages inside a1200.
keep in mind that ks3.x takes a while to boot.
oh, and check the temperature of chips.

[CDTV1991]

Originally Posted by johnim

try reseating the roms and try again but notice which rom from which socket and the end pin holes left see here

http://www.ianstedman.co.uk/Amiga/am...0moboR118.jpeg

Thanks, but I did this but it didn't make a difference.

If I unplug the internal FDD should the A1200 still boot?

Im trying to eliminate as much as I can

Originally Posted by orange

perhaps you should measure voltages inside a1200.
keep in mind that ks3.x takes a while to boot.
oh, and check the temperature of chips.

Anywhere in particular I should be measuring voltages?

Also, any particular chips to be checking the temperature of and what would suggest a fault? If one chip was "cold" would that suggest that it wasn't working or would you need to get the machine working to see some heat?

[orange]

yes, it should boot even without floppy (but, iirc, the delay is even longer then).
I'd measure the voltages wherever its convenient, like floppy power or perhaps parallel port.. (just be careful)
too cold or too hot is bad temperature for chips. still, alice and cpu should get pretty hot quickly. there are 4 ram chips, see if one of them is hotter than others.

[Arnie]

The 1200 will still boot without the floppy connected. Also the boot time is longer if 3.1 roms are fitted.

[CDTV1991]

When the machine is switched on all the chip temperatures range between 28 and 41 deg c.

The VLSI "budgie" chip, what ever it is does seem a little cooler than all the others.

What else could be bust on this machine to prevent it starting?

[cpiac64]

my 1200 don't boot without hard-disk, the signal reset is defect, insert an hard-disk or cf-ide with cf

change the rom 3.0 or 3.1, one time i received a 1200 with 2 rom odd, and verify if rom are inverted

[orange]

@cpiac64
perhaps you didn't wait long enough to boot.

[cpiac64]

sorry for my bad english, now use a traductor

"were my examples, I happened to have a 1200 that will not start if you connect a hard drive or a CF, then I've had with a wrong rom"

[Thorham]

Originally Posted by cpiac64

sorry for my bad english, now use a traductor

"were my examples, I happened to have a 1200 that will not start if you connect a hard drive or a CF, then I've had with a wrong rom"

If you mean a translator (traductor isn't an English word), then your 'bad English' is still a million times more clear than those translators

[CDTV1991]

The floppy doesnt click and the caps lock light won't come on, only a very brief flash when I switch the power on.

If I take the roms out it has no affect on the black screen. The tv thinks there is a signal, so some signal must be getting through, when i switch the machine off the tv goes back to a no signal screen

12v is reaching the floppy drive, 5v reaching various parts of the board

If I plug in the floppy but take out the power the orange floppy light comes on. If i plug the power in the floppy light goes out

I dont have any spare roms, however if I tried my roms from my a500, would they provoke some sort of reaction that may give me a picture on screen?

[cpiac64]

with tester read voltage on pin1 of hd connector, if zero the 10micro caps are dead, if 5 volt the reset circuit are ok, if you don't have a tester, use a led with a resistor 10k, if led go on the reset is ok

[CDTV1991]

Originally Posted by cpiac64

with tester read voltage on pin1 of hd connector, if zero the 10micro caps are dead, if 5 volt the reset circuit are ok, if you don't have a tester, use a led with a resistor 10k, if led go on the reset is ok

5v ok on hdd pin 1

I have a cf adapter, but no cable! If i touch the pins of the adapter to the mainboard the adapter's led lighht comes on so this must be ok.

So if its not power related it may be rom related?

Could i try an a500 rom?

[prowler]

Originally Posted by CDTV1991

So if its not power related it may be rom related?

Could i try an a500 rom?

No, they're not compatible with the A1200.