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Old 20 February 2013, 13:11   #41
demolition
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There are other things that can cause a black screen, like something as simple as the reset signal hanging, preventing it from ever starting. This would likely be an easy fix.

For someone with decent soldering skills and the right tools, it's not particularly hard to replace the CPU, although I don't think it's common for the CPU to die in an A600.
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Old 20 February 2013, 14:41   #42
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This may sound like a silly question but have you checked the kickstart rom to see if it is seated okay?
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Old 20 February 2013, 15:12   #43
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if you look at the kickstart rom theres (what looks like) two holes free... Ive seated it so all holes are used apart from the 2 on the left. Is that correct?

And.
If it is signal restart hanging do you know what the solution would be?

Cheers
Tony
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Old 20 February 2013, 15:20   #44
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Is the kickstart rom faulty?
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Old 20 February 2013, 15:21   #45
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On the PCB next to the ROM they have drawn some lines and arrows to indicate where the ROM chip should be. I think it is right that it should be located to the right.

I would test the reset signal using a multimeter. You can find it on pin 20 on the CPU. It is active low which means that 0V means reset. Thus, you should be able to measure 5V on that pin shortly after power on.
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Old 20 February 2013, 21:29   #46
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Is the Caps lock light on?, my A600 starts with a black screen with the caps lock light on - after 1/2 hour it boots - I think with mine I need to get the caps changed.
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Old 20 February 2013, 22:17   #47
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Quote:
Originally Posted by demolition View Post
On the PCB next to the ROM they have drawn some lines and arrows to indicate where the ROM chip should be. I think it is right that it should be located to the right.

I would test the reset signal using a multimeter. You can find it on pin 20 on the CPU. It is active low which means that 0V means reset. Thus, you should be able to measure 5V on that pin shortly after power on.
I can't see any drawn lines next to the rom telling me where it should be. Also where is pin 20 on the cpu. There are 17 each side.

As for the caps lock. it dosent turn on at all.

Last edited by trydowave; 20 February 2013 at 22:39.
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Old 20 February 2013, 22:41   #48
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Quote:
Originally Posted by Coltch View Post
Is the Caps lock light on?, my A600 starts with a black screen with the caps lock light on - after 1/2 hour it boots - I think with mine I need to get the caps changed.
Yep - I just fixed an A600 with that issue by changing the caps. I also had one where the corrosion lifted a pad. Doh. Not sure how I'm going to repair that one.

I think the caps are the most likely issue with the OP. OP if your not wanting to spend the ££ on cap replacement (you need some very small soldering iron bits if you were to do it your self) I would sell it spares or repair and keep an eye out for another.

Theres enough people around that will buy them to repair like myself and half this forum .
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Old 20 February 2013, 22:46   #49
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I noticed this under the kickstart rom. Damaged tracks. Is this really bad or superficial?
http://www.trydowave.com/amiga600tracks.web.htm
Cheers
Tony
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Old 20 February 2013, 23:24   #50
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Quote:
Originally Posted by trydowave View Post
I can't see any drawn lines next to the rom telling me where it should be. Also where is pin 20 on the cpu. There are 17 each side.
Edit 2: Here's a picture of the correct ROM placement:
http://www.bboah.com/download_photos/a600mb_rev15_2.jpg

Here's a picture of the CPU pin layout. Start from the dot (pin 1) and count counter-clockwise:


Edit: You can use the motherboard screw as ground for the minus-pin.

Quote:
Originally Posted by trydowave View Post
I noticed this under the kickstart rom. Damaged tracks. Is this really bad or superficial?
http://www.trydowave.com/amiga600tracks.web.htm
That looks like screwdriver marks from someone who wasn't careful when removing the ROM, and that could very well be the cause of your problem. Follow the tracks on either side towards a pad, and check for continuity with a multimeter to see if the connections are broken. Some of them look like they could be.
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Old 20 February 2013, 23:31   #51
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Your CPU pic isnt showing up demolition
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Old 20 February 2013, 23:36   #52
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Quote:
Originally Posted by trydowave View Post
Your CPU pic isnt showing up demolition
It's showing up here alright.

This is the link: http://megaburken.net/~patrik/pinout_temp/68000PLCC.gif
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Old 20 February 2013, 23:40   #53
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Hi got the cpu image now...

i have a multimetre in front of me now, how exactly do i check, What settings on the multimetre, what is the pad etc? This is all abit beyond me im affraid.
Cheers
Tony

p.s..... with the kickstart rom unplugged i get zero readout from the cpu pin 20
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Old 20 February 2013, 23:52   #54
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Quote:
Originally Posted by demolition View Post
That looks like screwdriver marks from someone who wasn't careful when removing the ROM, and that could very well be the cause of your problem. Follow the tracks on either side towards a pad, and check for continuity with a multimeter to see if the connections are broken. Some of them look like they could be.
Quote:
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i have a multimetre in front of me now, how exactly do i check, What settings on the multimetre, what is the pad etc? This is all abit beyond me im affraid.
You must set the multimeter to measure resistance (Ohms, Ω).

Next, because the pcb tracks are lacquered, you must follow the tracks on either side of the suspected break, as demolition says, until you find solder pads to make good connection with the multimeter probes. Then look at the multimeter display, which should indicate close to 0.0Ω if the track is not broken, or some higher resistance or maybe even an open circuit (blank display) if the track is broken.

To repair the track, you need to remove the lacquer carefully on either side of the break with a modelling knife or scalpel and solder a wire across the break.
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Old 21 February 2013, 00:04   #55
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I tried to do as you instructed. Set the mutlimeter to Ohms 20 and 200. I measured the broken tracks and the multimetre didnt move, some pins it did, most it didnt.

Not sure if I was doing it right. Its really tiny, i might need a magnifying glass.
My soldering skills are bad and thats repairing thing on a much larger scale than this. I might have a look around to see if anyone does repairs (and its worth the cost)

Last edited by trydowave; 21 February 2013 at 00:11.
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Old 21 February 2013, 01:10   #56
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Hi,
I just came across these threads, and wanted to comment on it.

A couple of things to remember/check from [me], a previous power supply tech.
First of all, although I am not familiar with an A600, I can guarantee the power supply is a switcher. They are lighter, smaller than a linear, and work great for computer use. However, when you measure output voltage, the +5 volts MUST be loaded. This means, as someone else mentioned, that the power supply must be connected to the Amiga, to get an accurate voltage check. BTW, most power supplies I have seen have an overcurrent feature, at least on the +5. This means that if there are any shorts on the board, (such as a bad cap) the power supply will shutdown until the short is removed and repaired.

About the continuing threads about bad caps. Sometime in the past, (If I remember, during much of the Amiga-lines production), many caps were installed that were defective and made in China. Many pc's had the same basic problem,and even during the warranty period. Although those of us that are handy with a soldering iron don't mind taking the time to replace the defective cap, the manufacturers lost a LOT of cash repairing the problems.

About the sockets used for chips such as the 68000: they are junk, and installed as a cost-cutting measure.

During the heyday of the Amiga, there was reportedly a factory bulletin that said if the Amiga had problems, drop it from a distance of about 4-6 inches. This would reseat the socketed chips, and often fix the problem even if for just a little while.

I had these kind of problems with my 3000T, and I ended up replacing all the offending sockets with very high quality gold-plated ones. Fixed those problems forever. However, it took probably 24 hours (or so) to desolder the old sockets, (The worse part) and put the new ones in. Don't try this unless you know what your doing, and have a professional desoldering tool and know how to use it. The traces are very easily damaged on these boards.

Last edited by tesla; 21 February 2013 at 01:23.
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Old 21 February 2013, 10:10   #57
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Not all the Amiga power supplies are SMPS - the original C= PSU I use for the A600 is one of the heavy transformer types, but you are right that most of them are SMPS. I'm not exactly sure when they used one type or the other. In any case, it's usually better to measure the voltage in the Amiga, so the PSU is loaded properly.

And the A600 doesn't have sockets (except for the ROM) as all ICs are SMD mounted PLCC, so in that regard it should be more reliable than the A500 design. Its main problem are the aluminium electrolytic caps, but I don't think it's because they are of low quality, seeing as they lasted 10-15 years before they had problems.
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Old 21 February 2013, 12:53   #58
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bad Caps

I have a 1961 Hammond organ. It has 3 tube (valve) amplifiers, one preamp, 2 power amp. All 3 have the original electrolytic caps. and all 3 still work. Many tube devices from that era, (no solid state yet) still have functioning electrolytic caps.

I guess they don't make them like they used to.


PS....your right, I had forgotten. My old 8-bit Commies had linear power supplies.


Quote:
Originally Posted by demolition View Post
Not all the Amiga power supplies are SMPS - the original C= PSU I use for the A600 is one of the heavy transformer types, but you are right that most of them are SMPS. I'm not exactly sure when they used one type or the other. In any case, it's usually better to measure the voltage in the Amiga, so the PSU is loaded properly.

And the A600 doesn't have sockets (except for the ROM) as all ICs are SMD mounted PLCC, so in that regard it should be more reliable than the A500 design. Its main problem are the aluminium electrolytic caps, but I don't think it's because they are of low quality, seeing as they lasted 10-15 years before they had problems.
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Old 21 February 2013, 15:41   #59
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I have a 1961 Hammond organ. It has 3 tube (valve) amplifiers, one preamp, 2 power amp. All 3 have the original electrolytic caps. and all 3 still work. Many tube devices from that era, (no solid state yet) still have functioning electrolytic caps.
I guess they don't make them like they used to.
PS....your right, I had forgotten. My old 8-bit Commies had linear power supplies.
It is all a question of size, performance and price. The requirements inside the organ are surely much different than those of a computer. The ones in the Amiga has to absorb (relatively) high frequency ripple, while those in the organ are just for very low frequencies and probably have very bad inductive properties, which wouldn't be useful with digital electronics.
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Old 23 July 2013, 13:34   #60
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Hi everybody,

Tony sent this machine to me (I do Amiga repairs on occasion), so I thought I'd update you all with what I found.

The first thing I did was find out why nothing was happening.
Luckily I'd come across this fault before - C611 (100nF ceramic) is a capacitor that governs the reset signal. When it goes faulty, the input pin 2 to the IC555 is held too low, and the 555 just holds the /KB_RESET line low, which in turn stops the CPU and all the other chips from doing anything at all.

That fixed, I checked the damage under the kickstart ROM. No problems there, all connections seem good. One track is damaged, but only superficially. Excellent.

Turning on, the screen came up with a dull green, quickly fading to black. That's not good.
Now things that fade normally imply dodgy capacitors. So the next step was to replace all the electrolytics.

That done, powered on.... screen flashes.. and again.. and again..
This isn't right.

Stick the Kickstart ROM into another A600... and it doesn't work! Put a known good Kickstart ROM into the dead A600 and it comes up - in green! That was with composite video. Try with RGB by using an A520 and it's perfect. Try with RF, and it's green... no, it's correct!
Go back to composite, turn off then on... screen is green... no, purple! Correct!

Turns out it just takes a bit to warm up (about 30 seconds from cold). I have no idea why, but once it's started up it's perfect. I'd guess one of the ceramic caps is slightly iffy, but I don't think it's worth chasing that for now.

It's now sitting next to me running Putty quite happily.

It lives again!
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