A501 "restoration"

BLTCON0

Math inside
AmiBayer
Joined
May 7, 2011
Posts
2,221
Country
Hellas (Greece)
Region
Chania, Crete
Recently I got a revC A501. It tested fine, RAM and RTC, so I took it home and un-cased it, not really expecting any thrills.
Wrong! So battery was removed at once (photos 1-3) and the two caps and three resistors near it were cleanly resoldered.
Apparently mostly the ground plane has suffered, so on to scratching the corrosion away. A CR2032 socket, donated by a useless PC motherboard, was also test-fitted, and fits nicely (y) (photos 4-5).
Some cheap nail varnish was layered upon the exposed-after-scratching areas and it was time for the socket + diode (1N4148 used) installation.
This is fairly easy on such boards because of the two bridged (+) holes. So the diode can easily be mounted inline between the socket's (+) leg and the PCB, simply by breaking the bridge (photo 6), then installing the socket and soldering the diode on the underside of the PCB (photos 7-8 ).
Doesn't really look nice (photo 9) but it still works (photo 10) and hopefully it will remain like that for a good while :smile:
 

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Nice work! I got one almost like this also. All i had to do though was remove battery and clean her up.
And i have another memory expansion lying in a plastic bag where i've just snipped of the battery, i remove the worst stuff but i need to buy some lemon to neutralize it will go out and buy it now actually, a shame if she would suffer death by corrosion.

Where should i throw the batteries it's hazardous material right? (Cadmium) I accidentally throw the first one i remove in garbage but now i'm saving them in a plastic bag to take to station at intervals.
 
What a lucky escape for that piece of hardware!! Goodness I hate those old skool batteries, they have killed too many machines :(

Well done(y)
 
Thanks for the good words guys, it's now sealed again in its metal shielding and ready to go, now just to be 100% sure, is there a good utility to test chipmem? (it'll go in a hacked for 1 MB chipmem A500).

@imaga_050
Yep I squashed a lemon to get some juice for that purpose, I just poured it on the corroded areas and left it for half an hour (for each side), don't know if that's enough or if I should have taken more time.
 
Received another A500 yesterday and I was pleased to find a working A501 in its belly.


Need to take it apart and remove the battery. Hopefully the PCB is in good condition. I have a whole bunch of those button cell holders on hand, so I might replace the battery with one of those and a CR2032 cell.
 
Holy guacamole! That card had it coming. Glad you got it back in operation. Well done! (y)
 
An easier way is, to remove R913 and place the diode instead of it.

So you don't have to brake the bridge (y)

This is the way i did it on two different Versions of A501:
 

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Thanks for the good words guys, it's now sealed again in its metal shielding and ready to go, now just to be 100% sure, is there a good utility to test chipmem? (it'll go in a hacked for 1 MB chipmem A500).

I think i used memtest.lha for that purpose seems ok. You run it from the cli prompt and can specify addresses to test and how many passes it test.

@imaga_050
Yep I squashed a lemon to get some juice for that purpose, I just poured it on the corroded areas and left it for half an hour (for each side), don't know if that's enough or if I should have taken more time.

I think the most important thing is that the lemon gets in every corner so it neutralises the whole board, it should neutralize almost immediatle as soon as it intermingles with the base crystals, with these low quantities.
 
Nice one BLTCON0. I have one of these myself and has removed the battery which did not cause any visible damage. This was a nice way of placing the diode.
 
@imaga_050
Thanks for the pointers (y)

@storhemulen
Darksun777's way with the diode is also nice, after all the diode already causes a voltage drop so it can be seen as a resistor too (although I don't know how the diode's voltage drop compares to the R931's in this case).
But apparently there's enough tolerance that it doesn't matter, so not having to cut the link is quite welcome (y)
 
Resistors limit current. Diode has a voltage drop, its not the same.
 
@Bad_Ad84
So the equivalent resistance R = V/I of the diode should be considered only a "mathematical" after-property of it once the diode is functioning in a circuit, and not a native characteristic that allows one to freely replace resistors with diodes, if I get you right?
 
Also, I strongly advice to use Schottky diodes in the lithium hack. They have lesser voltage drop (around 0.2V in direct current and a low current leakage).

The the resistor used in the NiCd barrel battery is there to limit that goes into the battery, as the other way the power consumption is very low.
 
Is there a recommended Diode value for this mod?

edit: I am guessing a 1N914 would be ok?
 
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The cheaper Schottky diode you can find, that's the best. ;)

So anything (I really mean "anything") with more than 10V of reverse voltage and more than 50mA of direct current will work fine.
 
@thgill
The guide I read mentioned the 1N914 but I couldn't find one here (someone said they aren't produced anymore), so I used the 1N4148 as a substitute.
I didn't know about Schottky diodes but following rkauer's advice I'll use one next time I deal with an RTC. Just too lazy to reopen the A500 and re-desolder the A501's metal shielding now :roll:
 
Recently I got a revC A501. It tested fine, RAM and RTC, so I took it home and un-cased it, not really expecting any thrills.
Wrong! So battery was removed at once (photos 1-3) and the two caps and three resistors near it were cleanly resoldered.
Apparently mostly the ground plane has suffered, so on to scratching the corrosion away. A CR2032 socket, donated by a useless PC motherboard, was also test-fitted, and fits nicely (y) (photos 4-5).
Some cheap nail varnish was layered upon the exposed-after-scratching areas and it was time for the socket + diode (1N4148 used) installation.
This is fairly easy on such boards because of the two bridged (+) holes. So the diode can easily be mounted inline between the socket's (+) leg and the PCB, simply by breaking the bridge (photo 6), then installing the socket and soldering the diode on the underside of the PCB (photos 7-8 ).
Doesn't really look nice (photo 9) but it still works (photo 10) and hopefully it will remain like that for a good while :smile:

I did it exactly like you but i have a different issue now:

When my Amiga boots to Workbench, it finds the clock and displays a random date and time. When booting is done, i open a CLI window and proceed to set the date using the DATE command, which appears to work. However, when i write "setclock save" it says "no battery backed up clock found"! At this point if i soft-reset my amiga, it is unable to find the clock! Any suggestions? In my case I used a Shottky diode and soldered it with the silver stripe where the black one is shown there.

I also thought of reccaping my expansion to see if it solves my issue. I know the 2 blue electrolytic caps ar 16v 100uf but do you happen to know the value of c913?
 
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