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A500 Has No Video Signal At All


blainelocklair

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Hello everyone!

 

I just bought a "tested and working" A500 on eBay. The ad showed it booting to the Kickstart disk screen on an original 1084. I received the computer yesterday, along with a Gotek FDD emulator and an A520 for video connection. The A520 was tested by the Gotek seller before shipping and worked. I have tried connecting the Amiga 500 throug the A520 by composite and RF to my TV, along with the monochrome composite to my TV, with no signal at all. The TV just sits on "No Signal". Nothing is being output from the Amiga.

 

Here's what I've done so far to try to help the problem:

 

* Checked for +5, +12. and -12 from the PSU at the plug to the back of the Amiga. All are fine.

* Swapped the CIA chilps, no change. I read online that swapping these can impact bootup.

* Did the "warm touch" test of all major chips. All are warm, indicating at least power, except for Gary and the Kickstart ROM (Rev. 5 board)

* Pulled the Gary chip, very gently sanded the legs with a Magic Eraser, iso alcohol clean of chip, socket, and board.

* Pulled the Kickstart ROM and ME'd and iso alcoholed it.

* When the system first came home, the original FDD would click looking for a disk. It has since stopped. I've installed the Gotek and everything comes up fine on it.

* The drive light originally would turn green for about five or six seconds, then turn completely off. Since installing the Gotek, the drive light stays on consistently.

 

I've attached pics of the socket condition for the Gary chip, the current message from the Gotek, and the drive light.

 

Well, that's all I've got for now. Since everything was tested prior to shipment, I expected everything to work ok when it got here. Not so much. I can really use any help that you can provide with this. I've been without an Amiga for 25 years, which is just far too long. Gotta save this one and get it back in service!

 

Thanks,

Blaine

 

Forgot to mention: no 512K memory/battery upgrade ever installed, so no battery corrosion from the trap door side. Also, caps lock flashes red for about one second at startup then turns off. No further flashes.

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Edited by blainelocklair
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Ok, reseated Paula, Denise, and Agnus. Was super-careful to pry gently from both sides of the socket very slowly. Came out with no issues, socket intact. Cleaned the pins with Magic Eraser and iso alcohol, cleaned the socket with iso and q-tips. Gently reseated all chips. Fired it back up and no change. No signal to the TV at all.

 

Just to be sure, the Amiga can send a signal to NTSC TVs through the connected composite monohrome, correct? I've tried that and the A520's composite and RF, and nothing.

 

Something else I noted: I can turn caps lock on and off, but only about six times. It just turns off the light and leaves it off after any subsequent presses.

 

Where do I look next?

 

Thanks!
Blaine

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Ok, reseated Paula, Denise, and Agnus. Was super-careful to pry gently from both sides of the socket very slowly. Came out with no issues, socket intact. Cleaned the pins with Magic Eraser and iso alcohol, cleaned the socket with iso and q-tips. Gently reseated all chips. Fired it back up and no change. No signal to the TV at all.

 

Just to be sure, the Amiga can send a signal to NTSC TVs through the connected composite monohrome, correct? I've tried that and the A520's composite and RF, and nothing.

 

Something else I noted: I can turn caps lock on and off, but only about six times. It just turns off the light and leaves it off after any subsequent presses.

 

Where do I look next?

 

Thanks!

Blaine

 

Did you note the # of keyboard flashes? There is info on what it can mean here:

 

https://ftp.fau.de/aminet/docs/hard/errormessages.txt

IN CASE OF FAILUREAfter informing the computer that the self-test has failed, thekeyboard will then try to notify the user that it is in trouble. This is done by blinking the CAPS-LOCK light.  Here is the code:One blink	The keyboard ROM check failedTwo blinks	The keyboard RAM check failedThree blinks	The watchdog timer test failedFour blinks	A short exists between two row lines or one of the                seven special control keys

I use either a 1080 RGB monitor or an Indivision ECS with my Amiga so can't offer any experience with the A520.

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It's strange, isn't it? I can't imagine why a signal for NTSC composite that would work with a CRT wouldn't work with an LCD. All of my retro consoles connect just fine. This one just doesn't seem to want to put out a signal. I see that there are "black screen" issues with Amigas, but this is beyond that. The TV just says "No Signal" and never even recognizes something is there. It timers out and turns itself off (the TV does).

 

I don't have an oscilloscope or logic probe, but if one is needed at this point, I might consider it. I could just file a grievance with eBay and get a refund, but I know exactly what will happen to the Amiga when it gets returned to the seller: thrown in the trash. That's a horrible fate for an Amiga; it deserves better, and I hope we can sort this one out.

 

Thanks everyone!

 

Blaine

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I wonder... does the "blank screen black" error refer to the Amiga intentionally putting out a black color to the screen or just the absence of signal on a classic CRT? The 1993 Amiga troubleshooting chart suggests that the "blank screen black" problem could be from the 68000 or the crystal. I haven't tried reseating the 68000, so I'll at least give it a try later this evening. Nothing to lose!

 

Thanks again to everyone that is helping me with this. I really to appreciate it!

 

Blaine

 

Got home, reseated the 68000, no change. Tried a different TV through the A520 and mono composite out the back of the A500, nothing.

Edited by blainelocklair
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Can you take a very close look at Pin 27 of the Gary chip. From the picture you sent it looks like you might have something sitting in the socket, and its possibly some of the coating of the bypass cap that sits to the right of the chip.

 

It looks from the picture as if that little capacitor might have lost of the coating at one end.

 

It's just possible with the jostling in transit something got stuck in there and is preventing the Gary chip from working.

 

The Amiga will boot up without the keyboard. If you suspect there might be a short on the keyboard just unplug it completely.

 

Does the Gotek make a noise when it is accessed? The HxC's can, and in these circumstances it can be helpful to listen for signs of life. Once powered up, wait a few seconds and then hit CTRL-Amiga-Amiga and check to see if the disk shows signs of being accessed. Obviously plug the keyboard back in for this exercise.

 

High res pictures of both sides of the motherboard would be helpful here. At least we could check for swollen caps, damaged traces or anything obviously amiss.

Edited by oracle_jedi
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Well, I would say I am a bit embarassed, and I am, but also not really. Everything is working fine on the Amiga. As it turns out, I found the problem through the "If you eliminate the impossible, whatever remains, however unlikely, must be true" principle. First, I tried a different TV (newer) to see if it'd make a difference. It didn't. I finally decided to check the continuity on my composite cable, even though it was brand new from Amazon with gold plating and shielding. Turns out, no continuity in the yellow part of the RCA cables. Grabbed a different cable and tested for continuity. Found continuity immediately. Hooked it up to the Amiga, and picture appeared immediately. Dang.

 

You know, it's so often the simple stuff that gets us. I would not have suspected that quality gold plated, shielded cables would have ever been the problem. But, they were. At least I also now have a very clean Amiga with cleaned chips, all reseated, and ready to go! Even got the Gotek to load its first game. You know it would have to be the one one in the pic.

 

Thank you to everyone that made suggestions and inputs into this problem. A good reminder to me to never trust, always verify. It's wonderful to have this Amiga back in business!

 

Thanks!
Blaine

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  • 2 years later...

You didn't even have to replace any of the sockets, I replaced some sockets and Stull nothing.

I have an amiga500 Rev 5 also that has a similar issue, I could check try some different cables, I had a shielded hdmi cable that stopped working, so for analog signals you have to make sure that it's something that will actually receive the signal.

If it's not a strong enough signal, most digital tv's don't display a signal.

 

My amiga definitely has a problem that needs close attention, I've replaced all of the sockets besides the CIA and agnus sockets, and I seem to have a boot loop with a gray or some kind of color of blank screen, just using the grayscale composite at the moment.

 I've also bought an extra set of chips besides agnus because it seems to be warm most of the time, and not much improvement.

  The Capacitors by the denise have also been replaced because one of them was shorted.

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Most modern LCDs, especially 

13 hours ago, Isaac Electro said:

You didn't even have to replace any of the sockets, I replaced some sockets and Stull nothing.

 

Most LCDs including TVs aren't compatible with the Amiga's video output signal. They do not support 15khz horizontal refresh, you can get lucky on this especially with older TVs that have a SCART input. So you might want to look into an upscaler like the OSSC which is what I use.

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Any TV should be compatible with the 15kHz horizontal refresh rate - that's the standard rate for analogue SD video, so if the TV has that connection (composite, S-Video or SCART), then it does support 15kHz video. The vertical refresh rate and colour encoding are different stories, and sometimes provide their own stumbling blocks, though colour encoding isn't relevant for an RGB connection. It's displays intended for PC use that often don't support 15kHz video.

 

Anyway, to go back a bit: it's great that you have it working now, but I wanted to clarify a couple of things regarding the caps lock key. A single flash of the LED is an indication that the keyboard started up normally - the troubleshooting quite quoted can often be misleading and refers to a repeating pattern of flashes, in this case a single flash every couple of seconds. If you can turn it on and off just fine, but only a few times and then it stops responding (as in your case), that's an indication of a fundamental issue on the motherboard, specifically interrupts not being serviced which usually means the CPU hasn't started. I suspect there was something else going on with the machine, and reseating the various chips at some point has rectified the problem.

Edited by Daedalus2097
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Yeah I will try a TV, and use my diag rom to see if there's an error code, I'm tempted to just make a direct connection my old crt TV board and make connections r,g,b, sync, and grd, right direct and see if that at least gives me a colored error screen, because otherwise, I can't really tell what is wrong with it.

Why couldn't they have just used beep codes for the amiga 500?

And the rev 5 board has got to be the hardest of the all to troubleshoot, I have an old-school oscilloscope, that I could use for troubleshooting, but I'm not sure what lines to test.

And I'm recapping it at the moment, so it should even work better, probably give higher sensitivity too.

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Ha, oops, didn't realise this was a thread necro, so my previous post is mostly related to a 2-year-old post.

On 12/22/2021 at 8:08 PM, Isaac Electro said:

My amiga definitely has a problem that needs close attention, I've replaced all of the sockets besides the CIA and agnus sockets, and I seem to have a boot loop with a gray or some kind of color of blank screen, just using the grayscale composite at the moment.

 I've also bought an extra set of chips besides agnus because it seems to be warm most of the time, and not much improvement.

  The Capacitors by the denise have also been replaced because one of them was shorted.

 

Sorry, I totally missed this post the last time... This is interesting, because when those capacitors fail, they sometimes take the video hybrid with them. That can mean severely distorted, or totally blank video output.

 

Beep codes would be nice, but that would have been additional cost for a machine that was intended to be as cheap as possible. Using the video output colour is a simple way of using the already existing hardware features to report a similar level of error. Using your oscilloscope, you might be able to tell what the R, G and B lines are doing, and thus determine the colour of the screen. But, as with beep tests on a PC, this will only give you a vague idea of the issue, not an exact diagnosis. This, of course, depends on the video hybrid being in working order.

 

Fitting a DiagROM and using a null modem cable to get the output is indeed a good way of troubleshooting a mostly dead machine. It can run with a very minimum of working hardware, including no working chip RAM. For me, DiagROM is a step I go to once there's no obvious physical damage - replacing sockets (unless clearly damaged) is only something that happens when I've confirmed that they're causing an issue.

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  • 3 weeks later...

Yeah, I could try connecting my Oscilloscope to the video output, and I do have a diagrom, not that it's doing me much good right now, because I don't have a colored output, and one composite/s-video adapter i did get, is setup for Pal and not ntsc! Very irritating.

And I got another video adapter to scart, but being in the US that really doesn't help me, I thought that I'd use a scart to hdmi adapter I got, but then learned, that hdmi stinks for analog signals!

So I'm extra dumb, and wondering what else could possibly be an issue, because this system has had so much stuff upgraded (all done by myself of course) , that I don't know if it did any good.

Sorry I know that this is an old post, but this was the easiest route, if anyone insists, I can make this into a new thread

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