Hardware & Technical Amiga tech expert wanted!

Tomtom

Tomtom
Recently I found an old friend of mine, huddled up in a box underneath a lot of other boxes.

QSxdNEh.jpg


IdpeYDb.jpg

She's been there for some time. She may be old and yellowing but she's still beautiful.

Anyway.

As I'm sure you will agree, she is the perfect subject for a restoration project, so that is what I'm now up to. First things first: take her apart for a good clean. I don't want to put any power through yet, just in case a thousand creepy crawlies have been using her as a toilet and shorted out something important and hard to replace.

Inside isn't as bad as I expected, but my cleaning did reveal this on part RP101 next to Gary:

OC7wRPu.jpg

That is one ugly blob of solder, shorting out the end two pins on whatever component that is. I need to know if those pins are supposed to be shorted, or if this is a manufacturing error. I've looked at a badly scanned service manual that Google found, but I can't make head or tails of it. I've Googled other images of Rock Lobster motherboards, but none that I've seen appear to have these pins shorted. I don't recall any major issues using the Amiga back in the day, but it did crash out every now and then - could this have been the cause?

If it needs to be fixed I can do it no problem, and if the pins are supposed to be shorted I can certainly resolder it properly - she deserves no less. But I do need to know how it's supposed to be before I start shunting electrons through.

So... those two pins: to short, or not to short?


Any other restoration tips or advice from anybody with experience is also welcome.
 
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AH_ImADot

AH_ImADot
I did a Google search for images of the Amiga 500 Motherboard. I did not see any that had those pins shorted. There are plenty of hacks out there for more on-board RAM, and other stuff, so I'm not sure if your MB has been tweaked or not. That's a pretty significant solder glob to make it through QA, and might even cause the computer to not even work if it was accidental.
 

clivewil

clivewil
by the look of the print underneath them, those contacts are both shorted anyway, yes? or is that just an illusion in the pic? (a bit hard to see exactly)

---> to me it looks like the last 3 in a row are common/shorted.
 
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Asp Explorer

Asp Explorer
That's a resistor pack. I don't have the specs handy, but you ought to be able to find an appropriate replacement. It's not meant to look like that :(

It's not part of a chip ram mod that I know of, it's nowhere near the cut jp necessary for that or have a flying trace wire.
 

Shadowdancer

Shadowdancer
Looks like a 4.7kΩ resistor network, each resistor being that value towards the pin to the left of the picture. The schematics I found look a bit weird (connecting Vcc to GND through one of the resistors seems useless?)

If you can get your hands on a soldering iron, some desoldering braid, and a multimeter, you can just remove that blob and then check if the value between the two rightmost pins is "correct". While measuring in-circuit isn't ideal, you should end up with a bit under 10kΩ.

(edit) While you're at it, just reflow all solder points on that resistor, they do llok a bit cruddy. Use lead solder.

- - - Updated - - -

clivewil said:
---> to me it looks like the last 3 in a row are common/shorted.
Click to expand...
I don't think so, they appear to be pull-up resistors for two data lines and that one resistor connecting Vcc to ground.
 
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Tomtom

Tomtom
clivewil said:
by the look of the print underneath them, those contacts are both shorted anyway, yes? or is that just an illusion in the pic? (a bit hard to see exactly)
Click to expand...

No, they are not connected, it just looks like that in the photo due to poor lighting and the camera being sort-of-okay-but-not-really-suited-to-this-purpose. By eye the tracks (and the gaps between them) are easier to see.


Shadowdancer said:
Looks like a 4.7kΩ resistor network, each resistor being that value towards the pin to the left of the picture. The schematics I found look a bit weird (connecting Vcc to GND through one of the resistors seems useless?)

If you can get your hands on a soldering iron, some desoldering braid, and a multimeter, you can just remove that blob and then check if the value between the two rightmost pins is "correct". While measuring in-circuit isn't ideal, you should end up with a bit under 10kΩ.

(edit) While you're at it, just reflow all solder points on that resistor, they do llok a bit cruddy. Use lead solder.
Click to expand...

Thanks, it sounds like you know what you're talking about! I have the soldering gear so no problem there. I fully intend to spend an hour or two refreshing my rusty soldering skills on a crappy old broken stereo before I go anywhere near the Amiga with it. Good idea about using the multimeter to test the pins - I shall definitely do that.


ArchEmperor said:
Omg. That is some serious treasure you got there! Take good care of it!
Click to expand...

Thank you, yes I will :D


Consensus so far is that the pins aren't supposed to be shorted, and I'm inclined to agree; I've looked at a bunch more photos and none that I have seen appear to have the connection, in good or bad solder. This Miggy was never modded, so that cannot be the cause either.

Still, there's plenty of work to do - need to finish cleaning the mainboard, de-yellow the plastic, strip and clean the keyboard, the floppy drive needs... uh... a miracle, and I need to pop the A501 expansion open for a look at that. Fully expecting the battery to have leaked.

I'll hold off on doing anything drastic for now, and while I do the rest of the restoration work I'll put feelers out for a couple more opinions. It's not that I don't trust you, it's just that she's precious and I'm taking no risks. I know you understand :)
 

Morbad

Morbad
It's hard for me to see from that picture, but on first glance that looks like one of the resistor in the network is damaged and has burst through the encapsulant, rather than being shorted by excess solder.

I'd replace the resistor network.
 

Hooplah

Hooplah
Let's hope that your Kickstart floppy disc is still working!

Also note that over time capacitors will fail especially in power supplies. Given 30 years running or not you might see a few of these which can be visually seen with leakage and/or bulging on the top end of them. I'd do a visual and replace as needed before applying power.

Failed-Capacitors.jpg
 

Tomtom

Tomtom
Morbad said:
It's hard for me to see from that picture, but on first glance that looks like one of the resistor in the network is damaged and has burst through the encapsulant, rather than being shorted by excess solder.
Click to expand...

Fortunately not. With a bit of prying I can fold the blob down, it is connected to the base of the solder points only, and the encapsulant is undamaged.


Hooplah said:
Let's hope that your Kickstart floppy disc is still working!
Click to expand...

Let's hope I can find it :eek:


Hooplah said:
Also note that over time capacitors will fail especially in power supplies. Given 30 years running or not you might see a few of these which can be visually seen with leakage and/or bulging on the top end of them. I'd do a visual and replace as needed before applying power.
Click to expand...

No worries there, the first thing I did was a full capacitor inspection and they look fine. A little research revealed that the A500 isn't particularly prone to cap failures anyway. When it came to manufacturing the A600 and A1200 though, Commodore opted for the cheaper SMD caps which are far less reliable!
That's not to say that the A500's higher quality caps can't fail - of course they can! But mine appear to be in very good condition. Thanks for the advice though, it is appreciated.


The verdict from all fronts is unanimous: those pins are not supposed to be shorted. Today I shall remove the blob and touch up the solder. Then I will inspect the power supply and if it all checks out I will power her up, for the first time in twenty years.

Wish us luck! :D
 

Shadowdancer

Shadowdancer
Electrolytic caps will over time dry out and fail without bulges or goo. So if the sucker turns out to not work, that's still something to keep in mind.
 
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Tomtom

Tomtom
Well...

She's ALIVE!

Boots up to the "Insert WorkBench Disk" screen just fine, but the colours are off - totally cyan, like there's no red component to the video output. The mono output feed looks perfect, so the problem is likely to be the A520 adapter itself (I hope!). This may be reparable - doing some research on it right now.

Otherwise all seems fine; no error codes blinking on the power light, the floppy drive is chirping away quietly to itself... it's wonderful :)
 

ArchEmperor

ArchEmperor
Tomtom said:
Well...

She's ALIVE!

Boots up to the "Insert WorkBench Disk" screen just fine, but the colours are off - totally cyan, like there's no red component to the video output. The mono output feed looks perfect, so the problem is likely to be the A520 adapter itself (I hope!). This may be reparable - doing some research on it right now.

Otherwise all seems fine; no error codes blinking on the power light, the floppy drive is chirping away quietly to itself... it's wonderful :)
Click to expand...

Please make a video of that moment. (I want to hear the sounds, see the screen, getting that nostalgia kick... ) I am filled with emotion. I am so happy for you!
 
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Tomtom

Tomtom
Good news, everyone - the A520 module has been repaired! A squirt of contact cleaner into the pots brought some colour back, but the red component kept flickering off and on. I reflowed the solder on the main socket connections, and now it's working like a charm.


ArchEmperor said:
Please make a video of that moment. (I want to hear the sounds, see the screen, getting that nostalgia kick... ) I am filled with emotion. I am so happy for you!
Click to expand...

At the moment I have the floppy drive in bits. There is a ridiculous amount of dust and fluff in there, I'm having doubts about whether it will be able to read a disk ever again. Even if that is the case, I'll see what I can do. The periodic chirps on the "insert disk" screen are still music to my ears, even if no disks can be read!
 

MickyG1982

M
amigacooke said:
At last, a thread where everyone is happy :)
Click to expand...

Can never be unhappy when there is an actual Amiga involved!!!

- - - Updated - - -

Tomtom said:
Well...

She's ALIVE!

Boots up to the "Insert WorkBench Disk" screen just fine, but the colours are off - totally cyan, like there's no red component to the video output. The mono output feed looks perfect, so the problem is likely to be the A520 adapter itself (I hope!). This may be reparable - doing some research on it right now.

Otherwise all seems fine; no error codes blinking on the power light, the floppy drive is chirping away quietly to itself... it's wonderful :)
Click to expand...

Maybe not repairable, but certainly replaceable:

http://amigastore.eu/en/4-amiga-500
 
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