A600 Caps lock led stuck on at boot solution

[PeteJ]

Originally Posted by jimbob

.. measure the DC voltage at pins 3,5,7 & 9 of U31. (if it reads 0, make the screen black)

Then change half the screen to black, (or white) and measure again

Hi, thanks I'll give that a try. I've ordered the replacement 74HCT244 so I'll run those tests first. I'm still learning about using the multimeter. It's a basic manual switch type. Do I put the negative probe to an earth and then check the pins with the positive probe when measuring dc voltage?

[jimbob]

Originally Posted by PeteJ

Do I put the negative probe to an earth and then check the pins with the positive probe when measuring dc voltage?

Aye, that's it. Let me know if this works. Even if green is all wonky, does it do what I think it will on the good colours data bit signals?

[PeteJ]

ok thanks, I'll try this during the week and let you know.

[mikele]

thanks kipper, life saving tutorial for my A600

[PeteJ]

The 74HCT244 arrived this morning. There's nothing that I can see to indicate which side pin 1 is on the original or the new one. I guess I should orientate it with the screen printed information in the same direction as the original one although that's not guaranteed to be the same. There is a notch in both of the chips so I suppose that must be what indicates which way to orientate it.

[Jope]

The notch is the only thing you should rely on, it is what indicates what end has pin 1.

[PeteJ]

Well I tried for an hour with flux and braid to remove the old one but it was stuck solid so I tried to cut the legs off instead and inevitably 4 of the pads have lifted off the board entirely when I eventually removed it I know that pads can be replaced but I think it's beyond me. I'm pretty gutted about it.

[PeteJ]

Originally Posted by Jope

The notch is the only thing you should rely on, it is what indicates what end has pin 1.

ok thanks for confirming.

[jimbob]

Originally Posted by PeteJ

Well I tried for an hour with flux and braid to remove the old one but it was stuck solid so I tried to cut the legs off instead and inevitably 4 of the pads have lifted off the board entirely when I eventually removed it I know that pads can be replaced but I think it's beyond me. I'm pretty gutted about it.

Ouch, sounds like you need some assistance. I hate to see amigas die and would offer but I am without my electronics gear at the moment. Did you try the test I suggested above?

For future reference, solder braid is not a good way to remove chips. It can practically never remove all the solder from a pin, a little "sweat joint" is nearly always left behind, the suction of the braid being too little for the adhesive force of such a tiny area of solder. The pin remains stuck to the pad and if you keep reheating, the bond of the pad to the board is permanently weakened as you have found. I find braid is only really good for cleaning up after components are removed. Hot air is the usual way but for small SOIC like U31 you can remove it by adding a blob of solder to each side bridging all pins, then alternate heating one side then the other until both blobs stay molten for a moment allowing you to quickly remove the chip.

[PeteJ]

Originally Posted by jimbob

Ouch, sounds like you need some assistance. I hate to see amigas die and would offer but I am without my electronics gear at the moment. Did you try the test I suggested above?

I did intend to but my disks are in storage away from home and I went ahead with installing the new replacement when it arrived that morning. I really don't want to let this Amiga die either, I did succesfully recap the board first (with the advice and details from Kipper2k) and that went well. I'm looking at the circuit frame repair kits, the type that don't need epoxy to be applied manually, the dry film type I think it was called. It looks straight forward enough from the instructions that I've read although the kits are expensive in the UK it seems.

For future reference, solder braid is not a good way to remove chips. It can practically never remove all the solder from a pin, a little "sweat joint" is nearly always left behind, the suction of the braid being too little for the adhesive force of such a tiny area of solder. The pin remains stuck to the pad and if you keep reheating, the bond of the pad to the board is permanently weakened as you have found. I find braid is only really good for cleaning up after components are removed. Hot air is the usual way but for small SOIC like U31 you can remove it by adding a blob of solder to each side bridging all pins, then alternate heating one side then the other until both blobs stay molten for a moment allowing you to quickly remove the chip.

I looked up various methods online before jumping into it, I saw some people had used a diy method whereby they fashioned a loop of copper to sit across both sides of the legs and then heat it up with the iron to remove it in one go. Others commented that they had done similar with a paperclip bent to size. I saw some of the You Tube videos demonstrating the hot air removal but I was worried about overheating the board or damaging components around it. Thanks for the explanation about why the flux and braid was not the correct method, I won't do it that way again that's for sure. I'll have to practice the hot air method with some junk pcbs in the future. I didn't expect the removal to be a problem, I was putting more time into learning about the drag solder method with a chisel tip to install the new one.

[FOL]

Got any pics of the damage.

If you dont use a rework station, you could use the heat one leg then lift with a fine screwdriver method. Its all about experience.
The loop of wire method, we used to use that back in the day before my previous company bought a rework station (long overdue, the boss didn't want to spend over £1000, which was the cost back then).

You should be able to get away with repairing the track with fine wire.
I have used this method loads of times when someone has sent a board to us they have damaged. 90% of the time, you cant even see where it was damaged.

[PeteJ]

Originally Posted by FOL

Got any pics of the damage.

I'll try and take some macro pics in the morning.

You should be able to get away with repairing the track with fine wire. I have used this method loads of times when someone has sent a board to us they have damaged. 90% of the time, you cant even see where it was damaged.

I'm not sure how to achieve that succesfully. Would I scratch off the solder mask just at the start of the track where the pad would have connected to and then solder the wire there at the length of the original pad? Wouldn't the wire move or bridge the neighbouring pin when I try to drag solder across the legs?

[FOL]

Originally Posted by PeteJ

I'm not sure how to achieve that succesfully. Would I scratch off the solder mask just at the start of the track where the pad would have connected to and then solder the wire there at the length of the original pad? Wouldn't the wire move or bridge the neighbouring pin when I try to drag solder across the legs?

If you use flux, then your fine.
I tend to look for decent anchoring points, sometimes the broken track goes to through hole contact. You can use that to solder to, you can normally push the wire through to make it secure.

[PeteJ]

Here's the macro photo of U31. My old phone isn't the best, I couldn't get it to focus correctly but hopefully it's good enough to see what I've done.

Four of the pads came away and a couple of others have partially come away from the board. The traces look intact however.

[FOL]

Originally Posted by PeteJ

Here's the macro photo of U31. My old phone isn't the best, I couldn't get it to focus correctly but hopefully it's good enough to see what I've done.

Four of the pads came away and a couple of others have partially come away from the board. The traces look intact however.

Please, closer, .
Im trying desperately to zoom in.

Quick look at schematics. You may be lucky and find the pads connected to nothing are broken.
However Im not sure the schematic is correct, think they just copied the A1200.
U31 is 20 pins, yet shows it as atleast 24 pins.

[PeteJ]

I've taken a further photo now which looks in better focus and is not scaled this time

[PeteJ]

Here's U31 from the A600 schematics pdf and the 74HCT244 pin outs

[FOL]

EDIT:- strach that, looking at wrong bloody manual, .

I can see from your pics, where the pads are supposed to go.
Best to scrap a little bit to expose copper, then beap out each borken track to where they should go.
Then use wires from that point to the leg of IC.

[PeteJ]

The schematics I'm working from is A600_R2.pdf that was linked in another thread here on eab.

Do you think doing a proper repair with the circuit frame kit would be easier?

[PeteJ]

Originally Posted by FOL

EDIT:- Looks like the official schematic is wrong, as its lists a completely different IC.

hmm, maybe that schematic is incorrectly listing the A1200 video circuit there as that uses a single PLCC for the video decoder rather than the two 74HCT244's that the A600 uses?

EDIT: lol I've just seen your edit, never mind