Troubleshooting a sick A1200

[Oldsmobile_Mike]

I'm working on an A1200 that won't respond to right mouse button clicks.

It appears to be the exact same problem described in this thread.

Symptoms:

• Early startup menu can be entered just by pressing the left mouse button
• Workbench does not respond to right mouse button clicks
• I'm able to access menus in Workbench with the ALT+RAMIGA key combination
• All pins on the connector are present and I've hit them with a little bit of contact cleaner
• 1D1 motherboard that does not appear to have ever been recapped
• Pressing on components like the CIA's and Paula don't seem to have any effect
• Tried with three different known-good mice (obviously)
• System is equipped with a Indivision AGA Mk1, Blizzard 1230IV + SCSI kit and a copious amount of RAM.  I could remove but I don't see how those could affect this issue
• My crystal trackball lights up on button clicks. It operates in the same manner on this A1200 as it does on my other Amiga's (bright for LMB, dim for RMB)

According to the second-to-last post in the above EAB thread, the culprit is C412 capacitor.

I've looked over the board and skimmed schematics here and here but I haven't been able to locate that component yet (if it exists) on this one.  I don't have the tools to replace SMD caps here, but any other suggestions before I page Dr. Acill?  ;)


Edit - just added a few random pics

[giZmo350]

My A.H. repaired A1200 board (I believe rev 2B) is asses-able top and bottom. Since I have it out, let me take a look... BRB.

[giZmo350]

A cap number is partially covered up on my board after repair but, look on your board... is it just above and to the left of the floppy header? It would be an electrolytic cap.

Nope, never mind. I see on your board it's labeled CN12. Dang it! Lemme keep looking....

[Oldsmobile_Mike]

Nope, never mind. I see on your board it's labeled CN12. Dang it! Lemme keep looking....

Thanks Rog!  This component may not even exist - at least with that part number.  

[giZmo350]

Sorry Mike.... I can't find a C412 anywhere... top or bottom. I checked all SMD's & Ceramic's.

However (not trying to hijack here), I'm glad I removed my bottom shield and checked there too 'cause I have two blown ceramic caps! C16B and C18A :eek: What the heck do those do? :cry:
 
 Ahhh, I see they are both part of DRAM Decoupling circuit.

Geeeeze! I wish Jens would hurry up and get those reloaded boards out!

BRB..... Ciggy time!

[jackflash]

CN12 is the floppy power connector, label numbers starting with CN are connector numbers

[giZmo350]

CN12 is the floppy power connector, label numbers starting with CN are connector numbers

Ahhh, ok. Then the SMD cap next to the floppy connector is C(X)22 (my number is partially covered up from a recap. On Mike's board it looks like C822.

[Oldsmobile_Mike]

BRB..... Ciggy time!

I'm still at the office, but will be doing the same shortly.  Working on these damned computers makes me need a smoke!  :lol:

[Chucky]

I had issues like this.  I also heard a slight low click in the speakers while pressingthe right mousebutton


fix:    capleakage have damaged the GND to paula..  of some reason paula still "worked" but RMB mouseclicks did not work.

[arttu80]

Hello Mike!

I think you should consider what I found out about my left mouse button problem. Maybe it would help your RMB dilemma also?

http://www.amiga.org/forums/showthread.php?t=66445

Read my last post in this thread please.

Also I noticed you have some odd colored pins on cia chip (U7) nearby keyboard connector, this CIA will affect joy ports. Something had been done to it?

[hese7]

I'm working on an A1200 that won't respond to right mouse button clicks.

According to the symptoms the computer acts like the right mouse button is constantly being pressed down. The Paula chip is responsible for handling the right mouse button. I suspect either the Paula chip is faulty or one of the pull-down capacitors (E353 or C312).

[QuikSanz]

In DC electronics a capacitor cannot pull up or down anything. This would be a resistor..

Chris
Tech Support
DoorKing

[LoadWB]

In DC electronics a capacitor cannot pull up or down anything. This would be a resistor..

Chris
Tech Support
DoorKing

Well, in its normal, proper operating state, no.  But caps can fail and go open or short.  Fun times.

[QuikSanz]

In series in a circuit they block DC. I parallel they "debounce", if they short you will get nothing out.

Edit: That may overload the resistor and blow it in time

[Acill]

Sorry Mike, I'm in Italy untill the 1st of January.