A600 Caps lock led stuck on at boot solution

[kipper2k]

Hi All,

Even though i am not at home i still can't stay away, so anyway, i got hold pf a really nice a600, really clean and white, but it had the caps lock led stuck on and the computer would just sit on the black screen. I took it apart and started nosing around and couldn't really see anything visibly wrong. most solder joints were shiny and the not so shiny ones did not look that bad.

I read up on some threads here and there and from what i seen a few people point to the 555 reset timer circuit.

here is a pic of that area...



i don't have access to any meters etc so i thought i would just remove the cap on the circuit...



so i got a pair of needlenose pliers and twisted off the capacitor as shown in the second picture.

I turned it on and away it went, booted up perfect. I also managed to pick up a TV with the SCART input too so that is going back to Canada with me (tested perfect . I'll put a fresh cap back on then too. The capacitor i removed did not look visibly bad so it goes to show it doesnt have to look bad to be bad

[jbenam]

Exactly the same conclusion I reached time ago, too bad that my A600 mobo was already entirely borked by experimenting by the time I thought of it

It should be noted that capacitors in that area seem to be very prone to leaking, and the electrolytes will interfere with the normal booting of the machine, as you found out.

Finally having this info here on this forum (reachable from Google too, hopefully) will help someone else in resurrecting his Amiga 600!

Great job, kipper

[roy bates]

i think i have mentioned to a few people that caps dont have to look bad to be bad.
its just more proof it can happen and does.

i dont know how well a esr meter works with these smd ones though..

[FOL]

Originally Posted by roy bates

i think i have mentioned to a few people that caps dont have to look bad to be bad.
its just more proof it can happen and does.

i dont know how well a esr meter works with these smd ones though..

Generally if they are bad, they will smell. Easy way to check is, iron one end, it will soon smell, .

@Kipper, the 22mf on the right have a nasty habit of leaking all the way down to the expansion connector, taking out mouse and joy port on its way, .

[kipper2k]

Originally Posted by FOL

Generally if they are bad, they will smell. Easy way to check is, iron one end, it will soon smell, .

@Kipper, the 22mf on the right have a nasty habit of leaking all the way down to the expansion connector, taking out mouse and joy port on its way, .

I think i will do a complete recap once i get home, can't do that much here.

[jolly11]

will it works without the cap? and if it will works, is it important to recap the circuit? which functions are managed by this cap?
thanks

[Coltch]

This cap was the culprit for my A600 not booting, removed it and as if by magic KS2 boot screen appears and works like a dream...Amigakit will probably have a mobo arriving next month for a new cap/re-cap.

Thanks for the info kipper2k I'd given up with my A600

[ElectroBlaster]

I have a couple A600's here with the same fault!

Amigakit will love me soon enough lol. Lots of my boards need redoing.

Already spent £550+ over a few years with these guys.

[kipper2k]

Originally Posted by jolly11

will it works without the cap? and if it will works, is it important to recap the circuit? which functions are managed by this cap?
thanks

Yes, it will work, but a replacement should be put back on the board, this controls the reset/initialization of the Amiga.

@Coltch, Nice to hear you have yours working again

[jolly11]

removed the cap, but black screen with the caps lock led stuck on again..don't know what to do now

[Coltch]

Jolly, have you cleaned the area where the cap was?..mine was a mess, quick clean up and it went from black screen to boot-up

[jolly11]

Originally Posted by Coltch

Jolly, have you cleaned the area where the cap was?..mine was a mess, quick clean up and it went from black screen to boot-up

the area look surprisingly good, no corrosion at all..btw, did you clean up your motheboard with vinegar/lemon juice?

[Coltch]

I used some IPA to clean the area

[jolly11]

cleaned the area in the other side of the motherboard and now it seems to work. thanks

[PeteJ]

Hi all, I have an A600 also with these symptoms. I've done a fair bit of soldering although I only follow instructions as I know very little about electronics. According to the information above, the cap that I need to change shown in the photos in the first post regarding the 555 reset timing, is that a 10UF, 25V cap?

If so, would a PANASONIC EEE1EA100WAR (CAP, ALU ELEC, 10UF, 25V) be a suitable replacement?



thanks!

[PeteJ]

Watching the You Tube video of the chap from Germany recapping an A1200 he replaces them with small ceramic caps instead (at least I think that's what they're called?) Could someone please tell me if that is an acceptable replacement and if so what they are so I can order some

Thanks.

[PeteJ]

I went ahead and removed the cap by NE555 carefully with needlenose plyers and sure enough the A600 is now booting although the video signal via scart was displaying incorrect colours. I don't know whether that will be caused by other bad caps or if the video dac is faulty, I forgot to test the composite output before putting it away. I'm guessing that the composite output might not be affected if the bad caps are part of the video out circuit? I hope it's not the video dac.

[PeteJ]

I went ahead and recapped the A600 motherboard today (recap thread: http://eab.abime.net/showthread.php?p=973895#post973895)

The problem with the colour output is still there however

The output is all tinted in purple and there is ghosting. It's the same through RGB scart and composite outputs.



There were four caps that I didn't replace because there was not enough clearance for soldering so I would have needed the parts in the way to be removed first which I really didn't want to risk doing: C334, C324 (near the keyboard connector) and C821, C822 (near the power connector).

I'm not experienced or qualified to know whether it's one of the tiny surface mouted resistors somewhere on the board that are at fault or if the cause is a faulty video dac chip. I only have a very basic multimeter which I've never used before so I will have to learn how to use that before I do something wrong with it and cause some further damage.

One thing I did notice was that after I removed the old caps and when I was cleaning off my flux and general mess from the areas were I'd worked with IPA, I noticed under the three caps C235,C236,C239 (which were all 100uf 6v incidentally) there seemed to be what looked like possible corrosion of the tracks in some small areas. It looked like the tracks had black patches here and there. Cleaning it thouroughly there with IPA and cotton buds didn't change it at all but when holding it up to the light I could still see the raised trace continuing in those spots so I reluctantly went ahead and put all the new capacitors in regardless.

Here's a photo showing the tracks in that area (circled in red) before I put the new caps in:



Maybe that is the cause? Does anyone know from the circuit diagram what those parts of the circuit are for and whether it will be causing the symptoms that are occuring? or, if anyone can shed some light on which other componets to test if that is nothing to do with it.

thanks very much.

[FOL]

Well you can rule out the circuit after the CXA1145 Encoder.
So its more than likely the encoder itself or something connected to it.

It looks like your missing Green.
Where the corrosion is, poke a needle through it and then tin one strand of wire. Push that through hole and solder both ends.
You will have to scrap away the lacker either side of hole.

Those caps only deal with Composite and RF. So I cant see that being the cause of your issue.
Have you replaced the NE555?

[PeteJ]

Originally Posted by FOL

Well you can rule out the circuit after the CXA1145 Encoder. So its more than likely the encoder itself or something connected to it.

It looks like your missing Green.

thanks, I should perhaps test the resistors in the video circuit next with the multermeter to see if one or more has failed. I will have a look at the 600's circuit diagram and try to understand what I'm looking at

Have you replaced the NE555?

No I've not replaced the NE555, I have replaced the failed capacitor there now that was causing the reset loop. When I googled the NE555 I read that it was a timer so I thought with the reset loop fault being caused by the bad cap there that this was used just for the systems startup / reset timing?