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Old 10 October 2016, 21:31   #1
bigbangtech
 
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Amiga 600 PAL no video

I'm in the USA, and have a PAL A600 from France that is not displaying any video.

>Boots from floppy
>Caps lock key works
>Capacitors don't appear to be leaking

I've tried using composite out a few weeks ago, don't remember seeing any video. (possibly due to my monitor being NTSC?)

I don't have an RF capable monitor or TV so I can't test that.

I have a cheap ebay RGB>VGA adapter, that works on my NTSC A500. So, I tried the adapter out on the PAL A600, and no luck. I get:

>Black screen with some garbled pixelated block lines (green) along the bottom and right of the screen.
>After booting workbench, moving the mouse does not change anything on the screen, so it doesn't look like anything is being output.

Any ideas on what to diagnose?

This is the RGB output that I can get:



Last edited by bigbangtech; 10 October 2016 at 22:45.
 
Old 10 October 2016, 22:11   #2
ajk
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Hi and welcome!

Do you know for sure that any of your displays can cope with PAL? Garbage like that could be due to the monitor being confused with the signal.

If the A600 has Kickstart 3.1 you could also try to switch between PAL and NTSC in the early startup menu (blindly), but I don't think that option was there with the original 2.05 Kickstart...
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Old 10 October 2016, 22:27   #3
bigbangtech
 
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My monitor with composite input probably only handles NTSC.

Correct me if I'm wrong, but RGB output from Amiga Video Port is neither NTSC nor PAL

It should be 15khz RGB for both regions, so if my RGB-VGA adapter can "see" my NTSC A500's 15khz RGB output, it should see my PAL A600's 15khz RGB output.

That's why I am assuming something is wrong with the A600.

If I were to get a hold of an RF capable tv set, would I be able to see anything? This seems improbable, as in the US, we use channel 3 or 4. I have no idea how RF works in europe.

I've tried holding down the mouse buttons to switch pal/ntsc, but I don't know what version the kickstart is, it had no effect.
 
Old 10 October 2016, 23:26   #4
ajk
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You are right in that the RGB output is not PAL, but it's still 50Hz which will upset many monitors (a common range is 56-75 Hz).

With RF both PAL and the fact that the output is 50Hz will most likely cause problems.

If you run a game or something that boots automatically, do you get audio etc. as expected?

A cheap way forward might be to get a video capture stick, perhaps something like the EzCap 116 (http://www.ezcap.tv/), which is multi-standard and will have no trouble with the PAL signal.
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Old 11 October 2016, 19:28   #5
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Hello Big Bang Tech. If you want to diagnose your Amiga, I offer to help you out with it if you want, I have PAL/NTSC displays to test with or I can facilitate you with a disk that would switch the machine to NTSC and boot a game so you can at least rule that out. Let me know, send me a private message (of course this is for free, just to clarify :P). Mailing within New York state would be really cheap, just gotta see if I actually have a disk around to send you.

As ajk says, you need a display capable of doing both 15Khz of horizontal scan rate as well as 50Hz of vertical sync rate. They are different things. No NTSC television I know of syncs to 50Hz.
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Old 12 October 2016, 03:48   #6
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Reverse here in England. I've never had a tv that won't display 60 Hz. They either stretch it to fill the screen or they leave black gaps at top and bottom of screen (my preference).
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Old 17 October 2016, 06:22   #7
bigbangtech
 
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I decided to change out the capacitors, and after messing up a few pads and having to make repairs, it didn't make a difference in the garbage video whether composite or rgb. Then, I decided to try a couple of things. I tapped RGB out directly from the CXA1145 encoder chip pins - no video. Next, I decided to bypass the CXA1145, and wired up to the RGB IN pins on the CXA1145 - bingo! I got video, but with some distortion probably because of the poor connection.

So is my CXA1145 bad and needs to be replaced? Or is there a way for me to troubleshoot it first? I don't have an oscilloscope. Maybe other caps or resistors are preventing the CXA145 from outputting composite or rgb? It outputs a black screen with green garbage as seen in my first post.
 
Old 17 October 2016, 08:51   #8
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It's certainly possible that the encoder is shot. Without an oscilloscope it's hard to diagnose it much more than you already have... if you feel that you are able to safely swap the encoder, that would probably be the best way forward. They are inexpensive chips.
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Old 17 October 2016, 17:09   #9
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Oh I am glad you figured some things out, I have your disk ready to be mailed anyway just in case you still want it (was going to post it today). Let me know!
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Old 17 October 2016, 17:11   #10
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Sure, I'll take that disk, it will still be helpful!
 
Old 22 October 2016, 21:23   #11
bigbangtech
 
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So, I replaced the CXA1145M video encoder chip, and hooked the composite out to a USB video capture stick and crossed my fingers...

Turned on the a600, and boom I got video - first a white screen, then I could see the insert workbench screen!

For about 5 seconds until the screen started to get a little wavy, then a lot wavy and then back to rolling static.

Great.

Its like the cxa1145 went bad after 5 seconds... What could cause this? Changing capacitors didn't make a difference even before I changed the cxa1145, so the probably don't have anything to do with this.

Looking at the schematics, I see that denise outputs RGB through a couple of buffers, then resistors then transistors before going into the cxa1145.

I'm wondering if Denise or something after is damaging the cxa1145 through the RGB lines, or if some other circuitry that provides voltage to cxa1145 is faulty and overloading it or not providing enough voltage/current.

I have no idea what voltages to be looking for in RGB side or power input to cxa1145.
 
Old 24 October 2016, 19:20   #12
bigbangtech
 
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I got a cheap USB oscilloscope from Amazon to try my hand at diagnosing things further. Here are some of the things I've measured, and what the cxa1145 datasheet indicates should be there:

On U12 cxa1145m video encoder:
vcc2 = 5v
vcc1 = 4.5v (don't know why vcc1 and vcc2 measured at different voltages)
pin 11 composite sync OUT 2.5v
pin 10 composite sync IN 4.5v (should be 0.8v to 2.0v peak to peak)
r,g,b IN 0.7v
r,g,b, OUT 0v

Now, since pin 10 should be getting less than 2v, but is getting 4.5v, I decided to trace where that is coming from.

composite sync to pin 10 on U12 is coming from pin 5 on the buffer U32 74HCT244, where I also measured 4.5v

Composite sync to U32 comes in on pin 15, and comes from U4 denise pin 35 (schematics aren't clear, so I had to trace this) this also measure 4.5v

Why is denise putting out 4.5v on composite sync if video encoder is expecting much less than that?

Next observation, after having the a600 on for 15 minutes, U4 denise is scorching hot, can't even keep a finger on it for more than 1 second. No other chip on the board is this hot. I'm beginning to believe the denise chip is bad. Supply voltage to video components (u4,u12,u31,u32,q211-213) checks out around 5v.

And once again, if I hook up a rgb-vga adapter to the rgb input pins on the cxa1145m(coming from denise,then buffers), I do get video, it's just fuzzy, so denise is outputting r,g,b at 0.7v. No video coming out of cxa1145 except garbage

Does anyone have a 8373R4PL denise on hand?

Last edited by bigbangtech; 24 October 2016 at 20:02.
 
Old 24 October 2016, 20:56   #13
ajk
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I've been working on an A600 board too so I checked the voltage on pin 10 of the encoder. It's around 4.5V so that seems to be normal (the video outputs on my board work, it just doesn't boot all the way).



It says 200mV for the scale on the screen there, but that's because I'm using an off-brand probe, so the scope doesn't know about the 10x attenuation.

The Denise does get pretty hot, although I wouldn't say scorching. If you do end up needing a replacement, guys like Sveta or tbtorro on AmiBay have a lot of spare parts, you could ask them. I think at least tbtorro is a member here aswell.
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