A1200 RF Modulator

[Solo761]

I recently got my hand on some Amiga goodies, one of them is A1200. Today I tried to see if it works by hooking it to my TV (LG 42lw579s) via RF out (RGB to Scart is on to do list). I set TV to channel 36 as manual said and kick 3.0 screen appeared.

The problem is it looked terrible. Colors were completely off and the picture was jumping. Or to be more precise here's the video of how it looks

[ Show youtube player ]

Is it the TV problem, after all digital TV is mostly used so perhaps analog tuner isn't all that "fancy" or is it modulator issue? I.e. something crapped out. Any suggestions? I tried trimmer on modulator and this is the best I could get. Other than that it works, I inserted a disk and it booted the game fine.

[Coltch]

RF always looks washed out and horrible, modern LCD's just make it look worse.

The only half decent RF picture I've had with my Amiga/Spectrum and PSOne is through a VCR connected via SCART

[diablothe2nd]

ditch the RF and use the yellow composite connector until you can get the RGB to scart adapter

[GadgetUK]

That flickering is possibly cap related. As others have said - ditch RF, use composite and if possible use RGB, and if you have the money consider Indivision and use VGA.

[Solo761]

Hmm, I'll have a closer look at caps around it then. I opened it when but everything looked fine at first look.

Of course, I intend to use RGB but I'd also like to have an option if it's already there . Currently RF out is unusable. Plus having it in good condition is always good .

Maybe recapping wouldn't be such a bad idea. It doesn't look that hard to do, it's just the matter of getting right capacitors.

[Sandro]

Originally Posted by Coltch

RF always looks washed out and horrible, modern LCD's just make it look worse.

nope
A1200 RF is good like composite video, if you use a descent and short armored cable, if you use a not armored cable the image will be a disaster
composite video is also affected by a buggy cable but not at the extreme as RF

[GadgetUK]

One of the main reasons the modulator will never be as good as composite, and the same reason composite will never be as good as RGB is due to modulation.

Demodulation results in the majority of the signals being seperated but it's never as clean as using discrete connections. RF on all my Amigas and ST sucks regardless of how good quality and short the cable is, and even on different TVs. The difference between RF and composite is highly noticeable, and the difference between composite and RGB is also highly noticeable.

[Solo761]

Well, it looks like it'll have to wait. It seems my TV (LG 42LW579S) doesn't support 15 kHz horizontal frequency, this is how it looked like when I used composite

http://i.imgur.com/cPgQECc.jpg
http://i.imgur.com/Xl2z1Oi.jpg

I tried via composite input (AV3 on my TV) and via scart using composite to scart adapter in scart input (AV1) in case only AV1 supported 15 kHz. I've read it's like that on some TV's, but not on mine. I also have small LED projector, Acer K11, same story, 30 kHz minimum according to specs.

I guess I'll have to wait for GBS-8200 to arrive, I ordered one yesterday.

I checked capacitors. Visually they all look fine. Only this one (pic from the net, not mine) has a dent on upper side.

[Arnie]

Any TV will display the Composite or Scart Picture, 15khz is not the issue here.

[demolition]

Yes, if the TV has a composite input, it should be able to show the Amiga picture. Composite is 15 kHz interlaced as default (can it be anything else?). Only thing I can think of could be PAL/NTSC problems, but I think the problem is with the Amiga itself.

[Solo761]

Oh boy... I hoped it was 15 kHz issue... This is going to be fun. Tomorrow I planned to make RGB to Scart, bought parts today (25 pin connector I planned on trimming down with dremel). I wonder how will it look like with it.

Unfortunately it isn't PAL/NTSC issue. Amiga is PAL, so is TV.

[Solo761]

Still no luck. I've made an RGB to SCART cable using Stedy's instructions, actually two, just to be sure. But it's still [ Show youtube player ].

I asked it Stedy's thread but no one answered. The thing I had to suppose was the orientation of the plug. Since scart looks that way (it's not symmetrical) when looked from the front I assumed it's the same with DB23. If you would put it horizontally pin 23, the one that has 75 ohm resistor would be on the left side, again, when looking at the front of the connector. When looking at the back, the side you have to solder at, it would be on the right side. Or better said it would look like this.



Is this correct or have I soldered it backwards?

There were tiny numbers on the plug (it was DB25 I trimmed down to DB23) but I've seen the same connectors that have number 1 on the left side, and then the same connector that would have number 1 on right side so that's not much help :/

[Jope]

They were not the same. Male and female connectors have the numbers running the opposite way. Makes sense when you plug them together.

So just look at the connector you have now, where is pin 1? That's the end where you should start to count from as well.

[roy bates]

i think you have the pin numbering the right way round,i'll take a guess and say you might have something wrong with the blanking pin on the scart side.
so,check your wirring and see what you come up with.

[prowler]

If that picture is showing the wiring side of the DB23 female connector you're plugging into your Amiga's RGB Monitor port, Pin1 should be at the left side top, Pin 12 at the righ side top, Pin13 at the left side bottom and Pin23 at the right side bottom, i.e., you have indeed soldered it correctly.

[Solo761]

Originally Posted by Jope

They were not the same. Male and female connectors have the numbers running the opposite way. Makes sense when you plug them together.

So just look at the connector you have now, where is pin 1? That's the end where you should start to count from as well.

In that case it's soldered correctly. I was hoping Commodore might have numbered them to differ from standard. That would be an easy way out of my problems, wrongly soldered .

Originally Posted by roy bates

i think you have the pin numbering the right way round,i'll take a guess and say you might have something wrong with the blanking pin on the scart side.
so,check your wirring and see what you come up with.

Cable in this picture isn't finished, it's missing PIN13 wire from Ian's schematic, just to be clear. Finished one has it .

I checked every pin (and neighboring ones), there weren't short circuits and every SCART pin had contact on DB plug, and resistance according to soldered resistor. Also, pin numbers are correct according to picture, I didn't swapped any of them.

But you may be onto something. My power supply looks fishy. On 12V rail it has 11.3V, and that's without anything connected to it. 5V looked OK, but who knows how it is when Amiga is making a load on it. Now, as far as I can figure it out, Amiga side should give 5V on blanking pin, reduced by resistor on that pin, I used 220 Ohm resistor (schematics says it can be from 75 to 270 Ohm). Maybe poor 5V rail and 220 Ohm resistor result in this [ Show youtube player ]

Originally Posted by prowler

If that picture is showing the wiring side of the DB23 female connector you're plugging into your Amiga's RGB Monitor port, Pin1 should be at the left side top, Pin 12 at the righ side top, Pin13 at the left side bottom and Pin23 at the right side bottom, i.e., you have indeed soldered it correctly.

I'm almost sorry I got it right . I'm starting to thinking it's my TV (LG 42LW579S), although it works with C64 via it's RF modulator. It's odd that both [ Show youtube player ] and [ Show youtube player ] would have the same problem. Unless it's PSU issue I mentioned above. I'll test that these days when I convert ATX PSU.




About RF modulator issue... I think it might me dead, I have the feeling that tuning screw is loose inside. No mater how much I turn it, to either side, it just stays rather deep inside, it's not moving up or down. So far I haven't found anywhere where I could order new or replacement one :/. If it's busted could it be the source of interference on composite out?

[alenppc]

Originally Posted by Solo761

But you may be onto something. My power supply looks fishy. On 12V rail it has 11.3V, and that's without anything connected to it.

Most Amiga PSUs that I have seen give a bit less than 12V on the rail, I don't think this would affect the RF modulator.

Originally Posted by Solo761

About RF modulator issue... I think it might me dead, I have the feeling that tuning screw is loose inside. No mater how much I turn it, to either side, it just stays rather deep inside, it's not moving up or down. So far I haven't found anywhere where I could order new or replacement one :/. If it's busted could it be the source of interference on composite out?

You should really try it with a different TV to make sure it's not the TV (sounds to me like it's a TV problem).

But, having said that, it might be possible to find a replacement TV modulator if you really want. I have a whole bunch of them that I removed from A1200 and A600 motherboards. I remove them systematically, since they are useless to me, and make it easier to replace the capacitors.

[Solo761]

Originally Posted by roy bates

i think you have the pin numbering the right way round,i'll take a guess and say you might have something wrong with the blanking pin on the scart side.
so,check your wirring and see what you come up with.

I checked it, pin 16 on scart connector is connected on pin 23 on Amiga video connector via 220 Ohm (240 actually, 10% tolerance...). No short circuits. I made two cables, both behave the same on this TV.

Electric anecdote... I checked voltage on pin 16 and Pin 18 (logic ground, which is connected to Amiga pin 13, also logic ground) and it was 4.95 V. At first I was surprised about that since the point of that 220 Ohm resistor is to reduce 5V to ~2.5V. But then I remembered how voltmeters work, they have huge resistance so if I measure it the way I did, I actually put huge resistance in series with 220 Ohm so when voltage is divided between these two resistances...

I should have measured voltage on 220 Ohm resistor while connected to TV to see exactly how much voltage goes to TV and how much is on the resistor .

Originally Posted by alenppc

But, having said that, it might be possible to find a replacement TV modulator if you really want. I have a whole bunch of them that I removed from A1200 and A600 motherboards. I remove them systematically, since they are useless to me, and make it easier to replace the capacitors.

I'm pretty sure TV modulator in my A1200 is faulty, fine tuning screw is loose, maybe it even short circuits something inside... I guess it would be best to remove it than have it faulty inside.

But I would like to have it as close to original as possible, that's why I would like to replace it with one that's not busted. Would it work on PAL A1200? I guess yours is NTSC. But all in all, I am interested.

[alenppc]

Originally Posted by Solo761

But I would like to have it as close to original as possible, that's why I would like to replace it with one that's not busted. Would it work on PAL A1200? I guess yours is NTSC. But all in all, I am interested.

The ones I have are all PAL. I can send you one for the cost of shipping if you like...

[Solo761]

I was productive today. I made ATX to Amiga adapter with these instructions, except I mutilated ATX24 to ATX20 connector and one molex power splitter cable instead of PSU connector. Seemed more practical as PSU stays unmodified and it's not tied to that specific PSU but it can be connected to any PSU. As long as it has 24 pin connector since 12V rail comes from 4 pins that 20 pin one doesn't have. But if need be it can easily be switched to need only 20 pin PSU.

I also desoldered my faulty RF modulator. Unfortunately neither that or new PSU didn't fix the problem, picture problem is still here. But at least I found out something new. There are few capacitors that have leaked. While desoldering modulator I smelled that famous fish smell. I guess these two are the (visible) culprits.

I noticed corrosion on the other side of motherboard, another cap whose legs are not shiny, but the one with green legs is IC U26 (TIF249 AS LS86A), but I doubt it's the culprit of my video problems.

So, after all this I connected it to new PSU, powered it on and... again the same thing as before. I left it that way, powered, as I pondered what to do next and then I noticed something. For few seconds there would be few parts of the picture visible, not always the same part, and the clear part would "float" upwards a bit before going haywire again.
This doesn't happen in regular intervals, it would be that way for 1-3 seconds, then gone for 10 seconds, back for 1-3 seconds and gone for a minute and so on, no regularities. The same thing happens with A500 so this time kinda think it might be the cable after all :/. Capacitors could be the reason why composite doesn't work.

This is how it looks

http://i.imgur.com/F0YoWCQ.jpg
http://i.imgur.com/bMeI3RK.jpg