A3000T Motherboard Help

[bitcpy]

Upon dissassembling and inspecting an A3000T that I recently acquired I noticed a blown resistor (if that is indeed what it is) at location C704 right next to the chip U704.

I am not well versed in electronics parts so I need some input on what part I need to order to replace the blown one? I am assuming that the blown component has not affected anything else and once I replace it, all should be well?

Here is what the board looks like:

 

[bdb]

It looks like a capacitor (probably died in the line of its duty protecting the IC)

 

[jvdbossc]

I am not sure it matters but u 702 misses a piece. There is also some discolorment. My bet about the cap would be it's just a stabeliser put to make sure no noise. But wait for somebody who can check chematics.

 

[LTAC]

I suppose that it's a caps, as bdb writes!
Label "R" = Resistor
Label "C" = Caps

---------- Post added at 13:30 ---------- Previous post was at 13:09 ----------

 

[vibros]

Hello,

this capacitor has the value of "224" -> 220 nanoF or 0.22 microF.

Regards
Stefano

 

[NMI]

Yes, that is (was!) a standard decoupling capacitor.
I have never seen one blow up like that though! :wooha:

It is not strictly required for the amiga to work, so just remove the remains and you can use the amiga till you get a new capacitor (and have the time to replace it).

 

[bitcpy]

Thank you so much guys!

I will look for the replacement part and in the meantime desolder this one.

 

[bitcpy]

While working on the board, I noticed 3 resistor packs were removed from the motherboard. Is this all part of the INT2 mod? Any reason why these packs would be removed?

 

[quarkx]

I may be wrong, but I think those are the termination packs for the SCSI. They are socketed, and right by the SCSI chip.

 

[bitcpy]

Ok.. That might make sense.. The computer had the WarpEngine installed with NCR SCSI so maybe you have to remove the termination resistors on the MB when the WarpEngine goes in.. I'll double check the manual.

Thanks for that. You may have answered it for me.

I may be wrong, but I think those are the termination packs for the SCSI. They are socketed, and right by the SCSI chip.

 

[BLTCON0]

While working on the board, I noticed 3 resistor packs were removed from the motherboard. Is this all part of the INT2 mod? Any reason why these packs would be removed?

As quarkx pointed out, these provide the option to terminate the onboard SCSI bus and they're intentionally left empty. Nothing to do with the INT2 mod. If installed they should be 220 or 330 Ohm.
You need to install these if the WD SCSI chip is at one end of the SCSI bus (e.g. only external devices, or only internal devices with the cable ending at the SCSI connector).

 

[bitcpy]

Thank you!

This 3000T is a bit different than my 3000D. The 3000T came with a SCSI termination pack that the quick setup guide says needs to be plugged into the back. I guess that is why the motherboard ones are missing.

On my 3000D I have no such SCSI termination pack for the rear connector. Wonder why the 2 systems operate differently.

As quarkx pointed out, these provide the option to terminate the onboard SCSI bus and they're intentionally left empty. Nothing to do with the INT2 mod. If installed they should be 220 or 330 Ohm.
You need to install these if the WD SCSI chip is at one end of the SCSI bus (e.g. only external devices, or only internal devices with the cable ending at the SCSI connector).

 

[quarkx]

Thank you!

This 3000T is a bit different than my 3000D. The 3000T came with a SCSI termination pack that the quick setup guide says needs to be plugged into the back. I guess that is why the motherboard ones are missing.

On my 3000D I have no such SCSI termination pack for the rear connector. Wonder why the 2 systems operate differently.

The 3000t was built as a separate project from the desktop version (not sure if it actually was before or After). It was a project to not only give a tower, but to improve the design and add more zorro slots, to be sold as an ultra high end workstation. (They were almost 5 grand when launched) One could guess that they assumed that no external SCSI devices would be added, with 7 internal drive bays, 7 devices is all one would ever want or need.
There was also some deal that was going to be made with SUN to use them as SUN Workstations (A3500)
Who knows what they were they were thinking with the puny desktop cases! I guess they believed that there would be no more need for a 5 inch drive bay since 5 inch floppies were obsolete. Maybe they got a good deal on those cases and just decided to cram it all in there.

 

[BLTCON0]

Maybe they got a good deal on those cases and just decided to cram it all in there.

Nice one!

My guess would be they got jealous of IBM's PS/2 series cases

 

[quarkx]

Yeh, you have to remember that CBM was notoriously cheap. The A1000 case was simply a C128 case "retooled" and the A2000 case was the failed C900 case.
The cases were an after-thought, they just used what they had lying around, and told the guys in Japan to "Make it fit". The Japanese team would then re-layout the motherboard to fit the case.
The A4000 case was also a re-used one, originally made for the "Improved" A1000 that nobody wanted (2200,2300,3200,3300- the A1000JR line) this was (IFRC) explained in the "On the Edge" book and here

 

[bitcpy]

I went to the electronics store to try and find the .22UF cap and this is the only one I could find.

I was hoping to stay true to the 3000T motherboard and find the same type.

Can someone please confirm for me that these are ok ?

---------- Post added at 15:16 ---------- Previous post was at 15:10 ----------


I tried to find them at Digikey but there are hundreds to choose from..


Does anyone know which category the right one falls into?


Aluminum Capacitors (64790 items)
Capacitor Arrays (1335 items)
Ceramic Capacitors (121174 items)
Electric Double Layer Capacitors, Supercaps (623 items)
Film Capacitors (19629 items)
Mica and PTFE Capacitors (3000 items)
Niobium Oxide Capacitors (469 items)
Silicon Capacitors (177 items)
Tantalum Capacitors (32843 items)
Thin Film Capacitors (2373 items)
Trimmers, Variable Capacitors (690 items)

Or even better yet, can someone point me to a location that will sell the same type of capacitor that is on the Amiga 3000T motherboard?

Here is all I could find locally.

 

[demolition]

I went to the electronics store to try and find the .22UF cap and this is the only one I could find.

Can someone please confirm for me that these are ok ?
I tried to find them at Digikey but there are hundreds to choose from..
Does anyone know which category the right one falls into?

This one is probably as close as you can get to the original one:
http://www.digikey.ca/product-detail/en/C410C224M5U5TA7200/399-4466-1-ND/818323

The one you got should also be okay to use, but it will look a little out of place. Remember to clean up the place from the blown cap using isopropanol and check that nothing else is damaged as well (tracks for example).

 

[bitcpy]

Thank you! I have ordered a bunch of them so I have spares.

I double checked everything else around it and it all looks ok.. I did clean the board with IP Alcohol as well.

http://www.digikey.ca/product-detail/en/C410C224M5U5TA7200/399-4466-1-ND/818323[/URL]

The one you got should also be okay to use, but it will look a little out of place. Remember to clean up the place from the blown cap using isopropanol and check that nothing else is damaged as well (tracks for example).

 

[demolition]

Thank you! I have ordered a bunch of them so I have spares.

They don't usually blow like that unless it has a defect (manufacturing, physical hit etc.), so don't expect to use the rest of them any time soon..

But I do the same as I hate seeing 90% of my money go towards postage, so I always order larger quantities to get that percentage down..

 

[bitcpy]

Exactly! They wanted $10 for shipping and $0.47 for a cap so I ordered $10 worth of caps.. lol..

Thank you! I have ordered a bunch of them so I have spares.

They don't usually blow like that unless it has a defect (manufacturing, physical hit etc.), so don't expect to use the rest of them any time soon..

But I do the same as I hate seeing 90% of my money go towards postage, so I always order larger quantities to get that percentage down..