another broken motherboard needs help :)

[loth77]

i have another motherboard with a problem...

i think the best way is to show it...



that in the schematics is (look the circle right side)



closer



as a result of the damage the A1200 has big problems with video output:
black screen in RGB and a black & white noisy output that at least shows that the motherboard is still alive.

i want to change that exploded component, but i can't understand what is the broken component
can anyone help me and this Amiga?

thanks thanks thanks!

[FOL]

Ouch, thats taken alot of current.

Looks like a Surface Mount Ferrite Bead.

[loth77]

mmm... yeah... seems like one of them...
with the symptoms i described, do you think that this could be the only damage in this mother board?
i can't see anything more

[FOL]

Originally Posted by loth77

mmm... yeah... seems like one of them...
with the symptoms i described, do you think that this could be the only damage in this mother board?
i can't see anything more

Check that print and see if it reads short to ground.
Seems odd it burnt up like that. Could only be massive current, causing it to cook.

Do some checks first, check the voltages, see if it has +12v. If it has, then maybe something connected to the RGB port was faulty.

[loth77]

yeah, i agree... very strange.
i'll check, then i'll have to find that smd ferrite bead

thanks

[Zetr0]

@loth77

Dadaaaaa click linkie its in itallian too ... yeah its because I care =D

Theres a minimum order quantity of 10 units - at 0.19 euros a unit that wont break the bank - however there is a minimum order process of 25 euros (i think its 25 ... it might be 20) either way I am sure you can find an absolute ton of stuff to add to make it up =)

good luck and remember to take photo's


its impressibe what kinda of things can cause such high current draw - those beads are supposed to only be rated for 300mA (0.3 amp) - since yours is on the +12v line thats a maximum of 3.6watts - what your picture shows.... is a "tad" higher than that - I would say that was pushin 40 - 60 watts

do you have any equipment on that line other than the monitor say an adapter like an A520 or SVideo adapter - if so its like thats broken as well... or has caused the problem in the first place.

[rkauer]

Also, the +12V line is only required to feed external adaptors, like scandoublers/genlocks or an A520.

Check the resistors near the trace to see if they are broken.

Oh, a SCART cable will use the +12V line, too: if you was using one, check for short-circuits on it.

[loth77]

thankssss
i'll find a way to order it (i have a friend who works in a satellite antennas repair shop and they often order from farnell.... so i'll ask him to add these little things for me )

about the problem... has been very strange.
i have built a rgb cable following a tutorial that is here on eab and this cable worked well on another Amiga that i have, but never worked on this.

i was using this amiga with an old commodore style cabletronic psu to keep it silent and all was working well. but i noticed that sometimes maybe it was lacking some power.

so i connected again the modified pc psu that i always used on my amigas.
before turning it on i also thought: "let's try again that home made cable on this amiga, maybe it was not working for the lack of power...."

turned on.... all black.... roasted silicon smell.... jumping on the turn off button... being "angry"....

that's it

tomorrow i will open the cable to check if there has been a short circuit there... it is strange, 'cos it was working well until few hours before on the other amiga.

so... do you think that changing the exploded grano di ferrite will give my amiga new life?
(she will be 18 years old on 21st december!!! i must save her!!)

thanks!


p.s.
@zetro... that ferrite bead you linked me is no more sold on farnell.
was that the exact "model" i need for my repairation? or just a generic link to the ferrite beads page?

[Loedown]

If you do a search for 1206 ferrite bead then you will be ok, 1206 is the package size.

You will most likely need to run new wiring, it's probably taken out the traces too.

[8bitbubsy]

The SCART cable will only use +12v (+ a resistor) to set the TV in RGB mode and to auto-switch channel. Set your TV to the AV1 channel and connect to SCART port 1 (RGB). This way the auto-set stuff is not needed.

I guess you actually fried something more than just this ferrite bead, because the +12v is not really needed for a SCART cable (or even a 1084 cable). Maybe the damage happened from inside the Amiga instead of from the RGB port... Please look carefully for other broken components... Check for fried chips: If you can't hold your fingertip on a chip without feeling burning pain, and the Amiga was only turned on for under 30 seconds, then you should have spotted a fried chip.

[loth77]

Originally Posted by Loedown

If you do a search for 1206 ferrite bead then you will be ok, 1206 is the package size.

You will most likely need to run new wiring, it's probably taken out the traces too.

thanks
new wiring seems to be not a big problem.

understanding the right ferrite bead is a bit more difficult, the one that Zetr0 linked is not a 1206 package size.
so i don't know what to choose now.

@8bitbubsy
i'm also scared to have fried something else...
but none of the chips is too hot when i keep the amiga on.
and also there are good possibilities that there has been a short circuit in the rgb cable.

i add a photo of the composite video output

[Loedown]

http://au.farnell.com/jsp/search/bro...001%2B1001113#

Measure the DC resistance and pick one that's close, or wait for a better reply from someone who knows more about these things, either Toni Wilen or Ian Stedman

[cpiac64]

sembra manchi qualche bit nel sincronismo, quei quadretti sono strani, scambia il chip video se puoi con quello di un altro 1200

p.s.
sorry if i wryte in italian

[loth77]

se potessi lo farei
ma non ho ne gli strumenti adatti, ne un chip da provare
conosci qualche posto in italia dove potrebbero almeno tentare di riparare questa scheda?

i said that if i could i would do that (exchange video chip)
and then i asked if he knows some place in italy where they still repair Amiga boards.

just in case i will fail

[Zetr0]

Hmmm looking at the pics I would say that the package type is 0805 (bigger than the 1202)

@loth27

try this farnel italian link if not try this Farnel UK link - worse case scenario theres always DigiKey - but there shipping prices can get scairyfor some parts of europe.

Now insofar as removing a working component from an A1200 its possible that its not the problem - the videoport is fed from the DAC - there are a couple of revisions made to the DAC on the A1200 though the revisions of the board - so you will need to start there - and replace like for like - you will notice that the DAC itself (pending motherboard version) will have 4 pins shorted and jumpered with wire on some motherboards - unless you have the same motherboard revision then you wont be able to use the DAC.

At this point I suspect the fault you are seeing is Capacitor feed related - so replace these very cheap components first - should that this not proove any different then I suggest that you change the DAC for the same revision you take off.

However its best to say at this point thats supposition - its as possible LISA has been damaged - the output / feedback on the +12v its quite serious - I dont think I have seen the +12V line on an A1200 light-up like that. FOL suggest a grounding to have or perhaps was - had taken place. I would certainly agree with that - so inspect the bottom of the motherboard as well - check all the localized resistors as well anything within the 12v rail (before the SMD ferrite bead)

as a thought it might be an idea to try another monitor - just incase the old one got damaged too.

Buona fortuna il mio amico. =)

[loth77]

thanks for the links

i would like to do all that you said... but i don't have a spare motherboard to sacrifice and i don't have the right instruments to do that, i just have a very simple soldering iron and a tester. apart from changing the ferrite and some caps in not too difficult places i can't do much more.

so i really don't feel like taking away components from the motherboard.
the revision is 1B
the dac has the pin shorted and the wire.
the lines looks really fine and i can't find anything strange near the resistors
i have found 2 capacitors that seems that have leaked, but they are very far from the video connector, thay are C821 (near that pcmcia) and C822 (near the floppy power connector)

can you suggest some places where i can send the motherboard to repair if i can't do it on my own?

unless it will not cost way too much, i would like to save this board instead of buying another.

edit...

about the screen i couldn't try one easily...
but i took the motherboard to the bigger lcd and connected it through composite output... results?
SHE'S ALIVE!!!!

but my shitty lcd screen seems that has troubles... well... it is just 2 months old, so warranty should fix it )
what do you think?

so now i think that the troubles of my amiga are less serious than before i will make some more tests, maybe i will just have to fix that ferrite bead to have back the rgb working

[cpiac64]

cosa intendi per "lei e' viva"?

io riparo un po' di tutto ma abito vicino a Milano

comunque te la stai cavando bene col saldatore

parli di lcd, puo' essere che non si sincronizzi col 1200

[Graham Humphrey]

English only please.

[loth77]

@cpiac
ti scrivo in italiano in pm

translation:
he told me that he repairs stuff and asked me what i wrote
i said that i will translate in pm

[cpiac64]

sorry,

i remeber to wryte in english.

the lcd in fault are broken the 1200