Amiga 500+ black screen

Tajmaster

Truth, Justice, all that stuff.
Joined
Sep 16, 2009
Posts
5,289
Country
UK
Region
Bradford, West Yorkshire
Hi all

I have acquired another A500+ recently but unfortunately it only displays a black screen.

Ive tried pushing all the chips down firmly and also swapped the 68000 and Gary for a known working one but it still wont work.

It had some battery leakage when I got it but it doesnt look that bad?? I cleaned it with lemon juice and then IPA.

Ive attached some pics, anyone got any ideas?

Thanks

Taj
 

Attachments

  • DSCF1718.jpg
    DSCF1718.jpg
    218.2 KB · Views: 4
  • DSCF1717.jpg
    DSCF1717.jpg
    219.5 KB · Views: 2
  • DSCF1719.jpg
    DSCF1719.jpg
    216.5 KB · Views: 3
  • DSCF1720.jpg
    DSCF1720.jpg
    206.5 KB · Views: 2
  • DSCF1721.jpg
    DSCF1721.jpg
    213.5 KB · Views: 3
Mine is the same does the floppy access just a little at boot ?
 
Mine is the same does the floppy access just a little at boot ?

Nope, the floppy light is off and the green light is "half dim", like it is normally before the insert disk screen would pop up.
 
oh right, well if anything yours is in slightly better condition than mine. my gary chip had been attacked too
 
I thought it might have been a duff Gary at first but swapping it with one from one of my A500s made no difference.

All the chips get warm but as there doesnt look to be much battery damage Im stumped :blink:
 
mine is just the same but i have a a little bit of an attempt to access the floppy. the motor spins one turn and stops...

cpu gets warm after a few mins...power light is steady but nothing else.
 
@Taj

looking at the Filter thats where your problem is likely to be.

You will need to desolder the resitors and diode and repair the power feed, to do this you should

1. Buy a fiberglass pen,

Fibreglass Abrasive Pencil & 5 Refills £6.75 + Free Postage (eBay.co.uk Buy It Now)



This is better for you than acetone, as its safer for you and the motherboard, I would suggest only those that have experience with acetone to use that as it will eat the entire PCB if you are not careful.


2. Buy conductive Copper Tape

Copper Foil Tape £0.99 Free Postage (eBay.co.uk Buy It Now)



Now this is really handy, this particular tape is used in whats known as Leading for stained glass windows, this means it can tolerated not only high temperatures but also the glue on the backing reacts with the heat causing a permanent bond with the substrate (glass / fiberglass) its adhering too


I will hit the schematics tonight and see if I can help anymore

---------- Post added at 17:55 ---------- Previous post was at 17:51 ----------

mine is just the same but i have a a little bit of an attempt to access the floppy. the motor spins one turn and stops...

cpu gets warm after a few mins...power light is steady but nothing else.

Hmmm this maybe a different but related problem my friend, the FDD has a power on self diagnositc routine which shouldn't have anything to do with the motherboard (other than supply of power which is done automatically with the power-on)

I shall have a thunk =D
 
Okay the area's that I would inspect here are

1. the Audio Filter Power feed needs repaired (look at Taj's last pic)
2. GARY socket needs to be buzzed out to the traces to ensure conductivity
3. Paula socket needs to be inspected for corrosion and conductivity

give that a go chaps.
 
The damage here (in the pic)

mine is exactly the same.. :)
 

Attachments

  • damage.jpg
    damage.jpg
    169.6 KB · Views: 6
Hi,
you also have a further look on the picture.

Best regards

FD
 

Attachments

  • damage.jpg
    damage.jpg
    195.2 KB · Views: 5
That needs some lemon juice pronto, to neutralise the copper hydroxide that is the blue fuzz on the parts. Clean off all of the blue crud with lemon juice, rinse and let it dry off and let's have another look.

That 74LS series chip is a signal inverter and that corroded leg could be carrying a signal that is holding the machine up.
 
Hmm, I thought I got all that gunk off :blink: Ill get a bit of lemon juice on it and see if I can scrub more off.

Thanks for suggestions guys and Zetro, I will purchase the stuff you have linked although my skills in this area are definitely in the n00b class category!
 
Oh, Ive always read that lemon juice is OK to neutralise acid?

One question about lemon juice, does it matter how old it is? ie, will it stop working if the bottle was opened say 3 months ago?

Anyway, Ive attached new pics. I took these after re-applying lemon juice, giving it a good scrub (the 74ls thingy, the Gary socket and the Paula socket especially) then scrubbing it again with IPA. Is it better than before?
 

Attachments

  • DSCF1727.jpg
    DSCF1727.jpg
    213.4 KB · Views: 1
  • DSCF1726.jpg
    DSCF1726.jpg
    207.7 KB · Views: 0
  • DSCF1725.jpg
    DSCF1725.jpg
    205.5 KB · Views: 0
  • DSCF1724.jpg
    DSCF1724.jpg
    205.2 KB · Views: 0
  • DSCF1723.jpg
    DSCF1723.jpg
    130 KB · Views: 0
  • DSCF1722.jpg
    DSCF1722.jpg
    157.5 KB · Views: 0
  • DSCF1728.jpg
    DSCF1728.jpg
    205.3 KB · Views: 1
well guys ive desoldered the resitors and diodes and ive started cleaning the area up - god it looks a mess :)

more fun tomorrow - one of the resistor legs fell off but i have new ones
 
@ Taj

If you aren't sure about your lemon juice, PM me some address details and I'll send you some citric acid powder - lemon juice in powder form - that will last indefinitely.

That board looks a lot better, but that leg on that 74LS chip will defnitely need refluxing and soldering.
 
@Taj

Lemon Juice (Citric *acetic* Acid) is used to neutralize Copper Hydroxide (Alkaline)

3 Month old lemon juice is perfectly okay.

IPA is good at lifting dirt/grease and resins but will not neutralize alkaline... well a lot of it would disperse it to be honest.

remember its best to wash the board with (deionized) water after the acetic acid treatment.

remember to give a good 10 minutes for the acetic acid to do its thing, then rinse, and apply IPA if you want to.

I would suggest at this point you use a multi-meter in continuity mode and check the traces leading to both the GARY and PAULA sockets


@Fieldday

My friend you will find the best PCB cleaners will contain citric acid as their *active* ingredient. IPA wont directly neutralize alkaline / base which what Copper Hydroxide / Peroxide is.
 
@ Fieldday

Citric Acid is used quite widely in metalworking circles as a 'metal brightener' and cleaner for non-ferous metals. It also has some uses in electroplating for the same reason. It's a relatively weak acid that doesn't have enough strength to etch the metal surface excessively.

@ Zeets

Citric Acid


Acetic Acid


They are a bit different, mate........Acetic acid is common vinegar.
 
that will teach me not to pay attention to chemical formula...

all though I got part of it right ;)
 
Back
Top Bottom