A2000 Rev. 6 not booting

[jasonsbeer]

Originally Posted by Malakie

I would start from scratch. Test the power supply and go from there.

Agreed. Your Amiga isn't getting past step 1. The diagrom will work without any RAM and most custom chips. Exceptions are Paula and U301, which are required to drive the serial port.

Double check you don't have any dead shorts. Resistance between the +5V and GND planes should be around 120-200 ohms.

Check the voltage at the 68000. Pins 14 and 49 are +5V. Pins 16 and 53 are ground. Check at those pins, not at the planes.

Check the reset line (68000 pin 18). Should be low for a second after power up, then go high and stay high for normal function.

Check HALT (68000 pin 17). Must be high for normal function.

Check the clock frequency at the 68000. Should be 7.xx MHz.

Also, puTTY serial settings should be 9600 baud, 8 data bits, 1 stop bit, no parity, and use a null modem. I assume you have that figured out, but never assume.

[roadrash]

Originally Posted by Malakie

I have been working on restoring a couple Amiga 2000's here as some know. The black screen can be caused by a whole lot more than just a bad chip or component.

For example, I got one of these boards working. Then yesterday, in fact, I was working on that unit and right in the middle of testing it, I got it to boot to Workbench when suddenly the screen went black.

At first I thought something I repaired failed. As it turns out, it is the power supply that just finally gave up the ghost. It has enough power to turn on the power LED, make the fan go, even cycle the floppy drive. But the screen never turns on. I used another power supply and this board is finally repaired but now the power supply has failed so now I have to fix that too.

The other board also has a black screen that I will be repairing soon. However that problem came from a power feedback through the floppy drive and a gotek drive that blew out while using it that I had connected externally. It blew the pico fuses and fed into the floppy drive itself. The machine again black screen. Even after I replaced the pico fuses, the machine refused to move from a black screen... UNTIL I unhooked the floppy drive. Once I unhooked it, the machine powered up again properly.

So the problem could be a myriad of issues and you need to think outside the box with Amiga systems. I am slowly getting back to my level of knowledge from 30 years ago, which helps greatly being I was a Commodore Technical Engineer back then. But even I make mistakes and am still re-learning much of what I knew 30 years ago.

I would start from scratch. Test the power supply and go from there.

Thank you for that info melanie it was most helpful.
I did check the power supply as you said and it is ok.
I have 2 of these 2000 models so tested this psu on my other working one. Many years ago I too was very involved with commodore and the Amiga and bought a A1000 at its uk launch in London. I used to visit the commode HQ in Corby uk quite often.
I did have to change the Rifa filter cap on the psu after it popped stinking out my house for days. But other than that it's been ok. I removed the original battery and cleaned up the motherboard around it. Only pip one of the cpu was slightly corroded and I cleaned that up and have tested all contacts. I replaced the battery with a coin cell battery and holder. I also did a recap and thought at first it was that but after checking them all many times I cannot find any that are a problem or put in the wrong way. So I am at a loss to know what's happened. I did also replace the cpu after I found that had failed unexpectedly but might have been careless handling of it when swapping around.
At least I have my other working B2000 to make comparisons and check readings from.
What and where are these pico fuses you mentioned?

[DigitalKeeper]

Typical Problem after leakage

-> Pin 1 to 8 & Pin 54 to 64 from CPU Socket <-

-

And - have a look to the VIAs UNDER the CPU Socket - here are often Break's

One thing is shure -> the CPU Socket must be changed!

[Malakie]

Originally Posted by roadrash

Thank you for that info melanie it was most helpful.
I did check the power supply as you said and it is ok.
I have 2 of these 2000 models so tested this psu on my other working one. Many years ago I too was very involved with commodore and the Amiga and bought a A1000 at its uk launch in London. I used to visit the commode HQ in Corby uk quite often.
I did have to change the Rifa filter cap on the psu after it popped stinking out my house for days. But other than that it's been ok. I removed the original battery and cleaned up the motherboard around it. Only pip one of the cpu was slightly corroded and I cleaned that up and have tested all contacts. I replaced the battery with a coin cell battery and holder. I also did a recap and thought at first it was that but after checking them all many times I cannot find any that are a problem or put in the wrong way. So I am at a loss to know what's happened. I did also replace the cpu after I found that had failed unexpectedly but might have been careless handling of it when swapping around.
At least I have my other working B2000 to make comparisons and check readings from.
What and where are these pico fuses you mentioned?

The pico fuses are on the board to try to protect primary circuits from damage if power is applied where it should not be. For example, if you are using a REV 6 board, they would be near the external floppy port labeled, F3 and F4. They would be green but can also be other colors.

These fuses are also found around most major ports on the board and a few other places. They should short. If you test them and they are open, it is bad and must be replaced.

Rev 4 boards name them a bit differently but they are the same purpose and use on the board.

With this board I am restoring, whatever was done to it, it blew both F3 and F4 AND toasted a Gotek drive, the DF1 drive, the CPU itself AND the power supply I was using to test with. The gotek and DF1 were with the board/machine when I got it. The power supply that came with it turns itself off after about 5 seconds of power up. So I plugged in my known good power supply and poof, now my power supply does the same thing.

Replacing those pico fuses, and the CPU and then using my last known good power supply I had here, and now the board boots up perfectly.

(now I have to tear it down to figure out what blew so I can also repair that - BTW, anyone reading this if you have seen this with the A2000 p/s and know what blew, please let me know.. would help in me fixing it quicker!)

[Malakie]

Originally Posted by DigitalKeeper

Typical Problem after leakage

-> Pin 1 to 8 & Pin 54 to 64 from CPU Socket <-

-

And - have a look to the VIAs UNDER the CPU Socket - here are often Break's

One thing is shure -> the CPU Socket must be changed!

Agree that GREEN on two pins of that 68000 socket could very well be the actual problem. That's pure acid corrosion from the battery. That socket has to be replaced, even if he gets it working, or it will eventually eat the pins off the CPU as well.

[DigitalKeeper]

Yep! It's ever the same problem:

-
-----

Have a look at the Marks!

And - UNDER - the Stencil of the PCB -> there are Breaks! Ya MUSt remove the white Stencil and clean the area

Also - have a look at the RP's

[roadrash]

Originally Posted by jasonsbeer

Agreed. Your Amiga isn't getting past step 1. The diagrom will work without any RAM and most custom chips. Exceptions are Paula and U301, which are required to drive the serial port.

Double check you don't have any dead shorts. Resistance between the +5V and GND planes should be around 120-200 ohms.

Check the voltage at the 68000. Pins 14 and 49 are +5V. Pins 16 and 53 are ground. Check at those pins, not at the planes.

Check the reset line (68000 pin 18). Should be low for a second after power up, then go high and stay high for normal function.

Check HALT (68000 pin 17). Must be high for normal function.

Check the clock frequency at the 68000. Should be 7.xx MHz.

Also, puTTY serial settings should be 9600 baud, 8 data bits, 1 stop bit, no parity, and use a null modem. I assume you have that figured out, but never assume.

Sorry for pause in replay as ive been pretty unwell.
There are no dead shorts but I get ground on pins 16 & 44?

[Vypr]

If you're getting GND on Pin 44 of the 68000 then that's and issue as Pin 44 is A16 (address bus) You might want to start checking that line for signs of corrosion, as it is shorting to ground somewhere.

[JHKrueger]

Originally Posted by Vypr

If it will help, I've just uploaded the PCB Layout and schematics for the Rev6 to Githubin KiCAD format

https://github.com/iansbremner/Amiga-2000-KiCAD.git

Absolutely brilliant, that layout file is an excellent debugging aid. Thank you for sharing.

- Jens

[roadrash]

Originally Posted by Vypr

If you're getting GND on Pin 44 of the 68000 then that's and issue as Pin 44 is A16 (address bus) You might want to start checking that line for signs of corrosion, as it is shorting to ground somewhere.

my mistake pin 44 was beeping my meter but its due to it connecting through C100 which if i reverse my probles make it beep but its not a earth. I still dont get a earth on pin 53 of the processor but ive traced pin 53 and if this is correct its connected to pin 28 on the kickstart rom and pin 23 on the CN608 slot. but its not showing as a earth.

[manmax]

I had exactly the same issue yesterday. Continuity test from ROM to CPU was all ok. I suspected the socket as pins 1 to 8 were green (supergreen). So I plugged male to female 2.54mm round socket strip, as I already found that it makes good contact with loose socket. Plugged CPU in and boom ! Boot to kickstart every time. So replacing socket is not an option.

[roadrash]

Originally Posted by jasonsbeer

Agreed. Your Amiga isn't getting past step 1. The diagrom will work without any RAM and most custom chips. Exceptions are Paula and U301, which are required to drive the serial port.

Double check you don't have any dead shorts. Resistance between the +5V and GND planes should be around 120-200 ohms.

Check the voltage at the 68000. Pins 14 and 49 are +5V. Pins 16 and 53 are ground. Check at those pins, not at the planes.

Check the reset line (68000 pin 18). Should be low for a second after power up, then go high and stay high for normal function.

Check HALT (68000 pin 17). Must be high for normal function.

Check the clock frequency at the 68000. Should be 7.xx MHz.

Also, puTTY serial settings should be 9600 baud, 8 data bits, 1 stop bit, no parity, and use a null modem. I assume you have that figured out, but never assume.

All the above voltages earths and states are correct. I was counting the wrong way for
pins 33 & 64. I dont' ?know where I check the clock frequency from.
Otherwise it seems everything is correct. What do I check next?

[roadrash]

Also, Puttty serial settings should be 9600 baud, 8 data bits, 1 stop bit, no parity, and use a null modem. I assume you have that figured out, but never assume.

I cannot seem to be able to get the A2000 to work over the serial port and to a PC.
Its nothing wrong with the cable or settings as I tried it on my other working A2000 and I could see all the details scrolling up in Putty. So there must be something wrong with this A2000 that is not letting the serial connection work. Any help please

[jasonsbeer]

Unfortunately, it becomes very difficult to troubleshoot these instances remotely. Suggestions in this thread would typically address most issues associated with a black screen. A couple quick thoughts...I have not re-read this thread, so apologies if these have already been discussed...thinking out loud here...

1) Gary is critical for start up after power on and reset. Bad connections to or around Gary will cause a frozen system at startup (as in no data or address bus activity). Check the connections and resistors around Gary and make sure they are not wonky.
2) Even though traces around the battery damage my tone out as having continuity, that does not mean they are suitable for carrying high speed signals. You could try jumping any questionable traces with wires directly to Kickstart or nearest appropriate location.
3) Parts cannon...when you overhaul these motherboards with battery damage, you are looking at replacing the sockets of the 68k, Kickstart, and probably Agnus. You need to desolder and check the values of the resistor packs and single resistors around the 68k. Replace if needed.
4) DRAM...in rare instances, bad DRAM(s) can prevent normal startup. Get some DRAMs and try piggy backing.
5)Are any chips really hot? I mean burning hot. This would indicate an internal fault.
6)Maybe the machine is starting up? You may have a problem in the video circuit that is causing a black screen. Hooking up a floppy drive will help here...does it click?

Unfortunately, without an oscilloscope you can only check voltage rails at the chips and throw random parts at the board. You can't check activity on the buses or other connections with any certainty. If none of these suggestions work, you may want to work directly with someone who can help repair the board. Good luck! I hate to see Amigas in critical condition.

[roadrash]

Originally Posted by jasonsbeer

Unfortunately, it becomes very difficult to troubleshoot these instances remotely. Suggestions in this thread would typically address most issues associated with a black screen. A couple quick thoughts...I have not re-read this thread, so apologies if these have already been discussed...thinking out loud here...

1) Gary is critical for start up after power on and reset. Bad connections to or around Gary will cause a frozen system at startup (as in no data or address bus activity). Check the connections and resistors around Gary and make sure they are not wonky.
2) Even though traces around the battery damage my tone out as having continuity, that does not mean they are suitable for carrying high speed signals. You could try jumping any questionable traces with wires directly to Kickstart or nearest appropriate location.
3) Parts cannon...when you overhaul these motherboards with battery damage, you are looking at replacing the sockets of the 68k, Kickstart, and probably Agnus. You need to desolder and check the values of the resistor packs and single resistors around the 68k. Replace if needed.
4) DRAM...in rare instances, bad DRAM(s) can prevent normal startup. Get some DRAMs and try piggy backing.
5)Are any chips really hot? I mean burning hot. This would indicate an internal fault.
6)Maybe the machine is starting up? You may have a problem in the video circuit that is causing a black screen. Hooking up a floppy drive will help here...does it click?

Unfortunately, without an oscilloscope you can only check voltage rails at the chips and throw random parts at the board. You can't check activity on the buses or other connections with any certainty. If none of these suggestions work, you may want to work directly with someone who can help repair the board. Good luck! I hate to see Amigas in critical condition.

Thanks ever so much for that info. When turned on, most of the chips warm up but not really hot just warm.
I did do a recap a while ago and wondered if there is any particular capacitor that if faulty or not connecting properly that would cause this failure to start up and just a black screen,

[LIV2]

When you power on the machine does the Power LED change brightness from half bright to full bright? Or does it just go from off to half brightness?

With Diagrom it should continue to flash for a while if it is executing the bootup ram test.

On top of what Jasonsbeer has recommended I'd also check the level of RST and HLT pins at the CPU which should start low at power up but then go high after a few hundred milliseconds if the reset circuit is working.

[roadrash]

Originally Posted by LIV2

When you power on the machine does the Power LED change brightness from half bright to full bright? Or does it just go from off to half brightness?

With Diagrom it should continue to flash for a while if it is executing the bootup ram test.

On top of what Jasonsbeer has recommended I'd also check the level of RST and HLT pins at the CPU which should start low at power up but then go high after a few hundred milliseconds if the reset circuit is working.

Thanks for that info it all helps a lot. I did do as mentioned above:

Check the voltage at the 68000. Pins 14 and 49 are +5V. Pins 16 and 53 are ground. Check at those pins, not at the planes.

Check the reset line (68000 pin 18). Should be low for a second after power up, then go high and stay high for normal function.

But it was all working as mentioned and the reset does go high a split second after power up and the voltages were correct. The power light just comes on but doesn't change brightness. There is no damage to the kickstart socket or agnus as I found the leaking battery before it got that bad. The only corrosion I can see is just one pin on the cpu socket which wasn't hard to clean up and a few resistors etc.
I will keep trying though.

[roadrash]

I have removed the processor socket, cleaned up all connection and fitted a new one (machined round pin type). I tested all connections of the processor socket before soldering in the new one and all were ok. Still have same issue of just black screen and power light does not flash. As you can see the kickstart rom socket is perfectly clean. I also started checking all the caps i had replaced earlier and did find one cap C802 I had put in a 470uf 10v when it should have been a 470 16v.
surely this couldnt cause this problem could it. I am jut waiting on some new ones arriving.

[Vypr]

Have you checked if RP900 is working properly? It looks like there's a chunk out of it at the top.

[RetroPassionUK]

Sorry to state the obvious you have reseated all the chips including agnus?