A500 Black screen

[NZJeux27]

Hi Everyone,

First-time poster. Have used these forums as an information source for a while but alas I've hit a wall with my current issue and need some specific help. I'm going to lay out the story so far so you have everything just in case it's even mildly important.

All photos of the project are https://photos.google.com/share/AF1Q...hsN1RQb0k1LW5Rhere for reference

I brought a Chicken Lips A500 to restore, cleaned it up, and managed to get a picture from the composite port to a screen I had. Now I live in the bottom of New Zealand and I am impatient so wasn't going to wait weeks while a workbench disk turned up from Europe, so i tried the amigaXfer floppyless bootstrap process, but I had issues with my serial cable (my converter was flipping the RX and TX and my null modem cable was flipping them back!).

I thought that the CIA chips were the issue for why it wasn't working so I thought I'd remove them, and re-insert them. I pulled them successfully and gave the socket a little contact cleaner and a light coat on the legs. I did the same for the ROM and on the comp port as well.

Now I just get a black screen, I am getting a signal but just nothing is showing, floppy clicks once and then stops. No lights or cap locks light showing ( i think this is a separate issue as they never worked)

I started by resocketing all the chips minus Angus (no contact cleaner this time) and using some iso-alcohol to clean out the contact cleaner I had used on the CIA/ROM chips. Nothing. I also replaced EMI401 after I blew it plugging in a mouse while the unit was running (which weirdly fixed the screen issues seen in the photos).

After a couple of hours with a guy of the Amiga repair group on FB, we found that CPU pin 17 & 18 were being held low and Pin 5 on Gary was also low. So I removed the KB and the pins went high but still nothing displaying or a reaction from the FDD waiting for a disk. I took the reset wire out of the KB to check, and the pins stayed up but again nothing on the display.

This is where I am at the moment, and not really sure what to try next. I read on here about checking the reset circuit or checking U37/U38 but IDK what I'm looking for, I probed them, and pin 1 on U37(?) was at 13.4v which i found weird but I forgot to check it against the specs. As you can see in the photos, the MB itself is in a good condition, all solder joints and traces are present, with no acid damage or simlar (unlike the 502 which is FUBAR)

I remember I didn't unplug my serial cable when I removed the CIA chips, and I wonder if I shorted something there. But again there could be multi-able issues at hand here.

I have a spare working Denise and CIA chip at hand, basic tools like soldering gear, and a multimeter.

Thoughts? My hardware problem-solving skills are fairly limited so I'm very much stuck.

Thanks in advance.

[Overdoc]

If you are not sure if your CIA chips are dead and perhaps shorted, then you can just remove them both - your Amiga 500 should then at least start up with a completely white screen.
If you only remove the EVEN CIA, then it will start up like normal, but it will take some seconds until the kickstart screen is displayed, just like if you there was no diskdrive present.

Apart from that, I would start with measuring the reset signal on the 68000 chip at startup.
Also check if 5V voltage is present on the chips, first?
The feel on every chip with your finger if any of them is getting hotter than others?

If you fiddled around on the serial port, then the MC1488/1489 chips may have gone broken? However, the Amiga should start up and work like normal even if they are removed, but they could prevent it from starting up correctly if shorted? (shorted chips will get very hot!)

[NZJeux27]

Hi Overdoc,

So when I did my testing with Thomas, he had me measure the voltage on pin (18?) on the CPU to do that, and with the KB plugged in it never raised past 0.04v during any point in the startup or post that.

When the unit is running only Gary (or was it Paula bugger i can't remember) is cold to the touch(however I can read voltages on pins as expected), the rest are warm. And touching all the chips i cannot feel one that is warmer than the others.

It could be booting fine with one or none of the CIA's but the comp port not showing it, but i will try that tonight.

EDIT: forgot to add, yes i am seeing voltages on at least the even CIA chip just didn't check them vs the specs again.

[redblade]

Hi NZJeux27 If all else fails contact this guy at http://www.amiga.serveftp.net/AboutMe.html Hoffman lives in CHCH and repairs Amiga and has spare parts. I would and do recommend him.