A600 + A604n not detected

[Storm]

Hello all,

My recapped A600 after years of working fine suddenly can't detect the trapdoor memory. I also have an Indivision plugged into the A604n. I still get a picture from the Indivision output, although it has some light jail bars about an inch apart across the screen. The Indivision config tool also can't detect the hardware. So it seems the Indivision is sort of working to some extent and the extra 1MB of chip RAM isn't seen. I initially thought it was a faulty A604n, and bought a new one, same problem. Anyone have any ideas where to start trouble shooting this?

I have done the usual process of cleaning the edge connector and checking the traces from the connector on the motherboard. Thanks in advance.

 

[AmigaDepot]

Maybe you pull out the ram expansion by a milimeter or two, this has often helped with trapdoor expansions.

 

[miggymad]

Remove the Indy and then see if the chip RAM expansion card problem still occurs. Also you can try reseating any chips that are socketed.

 

[Storm]

I've removed the Indy, used a different A604n and even tried moving the expansion a bit. Still no luck.

 

[miggymad]

The chances of 2 A604n's causing the same overall problem is negligible. Also since you have removed the Indy and are experiencing the same overall problem, the issue and your next line of investigation must lie with the A600 itself.

Check the caps, inspect around them closely and see if there are any problems there. Even with the best caps in the world they are still prone to failure.

Also check the voltages coming from the power supply. If you have another known good PSU then plug it in and see what happens.

 

[Storm]

I have tried several power supplies I have and the same result. The Amiga has been recapped in the last few years and I did test the traces to the caps and the edge connector with a meter. Maybe a cap has died and I should just replace some to see what happens. I'm guessing it's those little fellas that live under the disk drive

 

[miggymad]

Divide and conquer with the caps would be a good way to go about it, starting with those "little fellas that live under the disk drive" lol

Good luck, hope the patient gets well soon!

 

[Storm]

Well, I've replaced the capacitors and the A600 is still not giving me any love It's in the same state as before.

 

[Pinback]

expansion port has VCC at 12(?)V and reset line low?

maybe it is more promising to post this at a1k, exxos or eab?

 

[Storm]

I might try EAB as well, since I'm on there too.

 

[Pinback]

so you checked if the expansion port delivers power and its own reset signal is low after powering up?

 

[Storm]

If you could give me some guidance on how to conduct these tests, I will check it out.

 

[Pinback]

luckily i can. i pulled a a600 rev1.5 board out of the shelf and quick checked the expansion port. multimeter voltage on pin 80 of the expansion port (the right most, "80" is written there on the board. it should deliver 12 volts (with just minor deviation). Be carefull not to send the 12v to some other contacts, if you slip with whatever you measure.
Pin 70, which is the 6th pin from the right, is the reset signal. on my board it shows 4.76v. anything near 5v should be ok.
Be aware i am no expert. i wont hesitate to ask someone else ;-)

 

[Storm]

Thanks for the info. Pin 80 on mine shows -11.95V and pin 70 shows 4.38V. It's weird that pin 80 is a negative voltage. Could that be the problem?

 

[Pinback]

it´s indeed the negative voltageline. right below it, on the bottom side, pin 79, there you have to have +12v, check that too. do you happen to have an oscilloscope?

 

[Pinback]

what´s in my mind: if expansion port isnt powered properly, it will fail in many fancy ways. and if the reset signal isnt propagated properly to the expansion port, it could have the same symptoms. now it would be interesting, how an expert would diagnose these to things. maybe it is prolific to ask for that other than a general expansion port troubleshoot... something like: which pins of the expansion port should have which reading in order to compare it with yours.

 

[Pinback]

another additon: you can download the schematics for your rev1.5 board at amigawiki. if you check the expansion port, you will see that the 12v line is on several pins. i guess you need to check all voltage lines. please be carefull not to fry your board when accidently shorting the 12v to the board. i would be inconsolable, when my ragged tips crash your amiga.

oh, i forgot the alltime classic: try another PSU.

 

[Storm]

Okay I now have a set of schematics on hand and I do have an old oscilloscope. Pin 79 shows 11.75V. I have tried two different power supplies so far.

 

[Pinback]

in the schematics you can see that the expansion port has several voltage lines. you need to check them. after that you check the signal lines with the scope. but you still need a reference what the scope should display, when the line is ok...

 

[Storm]

I have a friend that has a rev 1.5, I might have to do a direct comparison with his machine.