Need Help with a broken RF Modulator

[Paul Sernine]

Hello folks.

 

My name is Paul Sernine, i´m a videogame and console collector that have allways been very fond of owning an Atari 2600 system witch are quite rare where i live. I have finally have, and hope to be around this boards to extend my knowledge of the system.

 

However, I need help with my new toy. it´s RF modulator is not functioning, and i´m unable to find the correct soldering spots for the composite video hack.

 

I´ll better tell you the story from the begining.

 

I have recently come across an Atari 2600 witch acording to his previous owner was not functioning properly, the problem beeing he was not able to see a clear image on the screen. A first inspection of the console, leads me to think that is is a SECAM one (the stiker bellow says: "MODEL 2600CX-S", S standing for secam, i suppose).

 

I live in a PAL region, so i figured out that there was no misfunction whith the console at all, and the problem was the user conecting it to a non secam capable monitor.

 

After serious testing, whith the console connected to my PC capture card (whitch supports all kinds of SECAM), I am still unable to see a clear picture. Game below is Frogger.

 

 

Next thing I do, is try to adjust the potentiometers in the RF modulator, but then i find one of the potentiometers is badly damaged. I take for granted that it was broken by the prior owner, during a frustrating attempt to make the image show up on a PAL TV set. In the image is the one pointed by the arrow.

 

 

Then I decide to say goodbye to RF and go for the composite video hack, but after reading a whole bunch of tutorials, i find myself unable to simply identify my board. It´s a "four switch wooden front" but the board doesn´t even look close to none of the photos i´ve seen on the internet.

 

A photo of my board can be seen below.

 

 

Another option, would be to replace the damaged RF modulator. I don´t know if this can be achived easily, the modulator comes attached to the board by three soldering spots with no label at all, so i assume it should be posible to replace it with a similar one, either buyed new or recicled from an old VCR, I even have a broken down Genesis around whose RF modulator i could borrow.

 

My ignorance is great, the potentiall replacemente for the RF modulator would be a PAL one ¿will it work on a secam console?

 

In fact, i don´t even know if the console will work with the cartridges I have (which should be PAL). Are the 2600 cartridges region specific?

 

Any help identifying my board or rf modulator would be greatly appreciated. Thanks in advance for all the help.

 

PD: As you probably noticed, english is not my mother lenguage, so please spare the typos i certainly made, hope the text makes sense.

[A.J. Franzman]

Hello Paul.

 

Am I correct to believe that the SECAM television system is only used in France, and that therefore your friend most likely got this console from that country?

 

I believe that SECAM Atari 2600 consoles are probably quite rare, and hope that someone here is familiar enough with them to help you fix yours.

 

Most of the composite video modification instructions found online are for NTSC consoles, which you have already realized are quite different from your SECAM unit. I believe that there are instructions online somewhere for a composite video mod for PAL consoles but I have never heard of one specifically for SECAM consoles. However, chances are fairly good that a PAL composite mod will work for your SECAM console if you can find the proper circuit connection points (perhaps some small adjustment will be needed). If anyone here knows with more certainty, I'm fairly confident that you will get a better answer soon. To the best of my knowledge, both PAL and SECAM consoles use the same version of the "TIA" or "Stella" chip, which is the part that makes the television picture. That chip version has a different pin configuration from the NTSC version, which is the main reason why there need to be different composite video mods for the different regions.

 

Incidentally, the part that you have indicated as being broken is not a potentiometer but an adjustable inductor (also known as an adjustable choke). Since it appears that there is only a small part of the core missing, you may be able to make it work better by turning it further into the wire coil - if you can not turn it from the side shown, try turning it from the bottom side of the board, if there is a hole provided for you to do so.

 

I believe that you may be correct about your friend having problems only because the console is SECAM but his monitor or TV was PAL.

 

I do not know if the RF modulator from a PAL 2600 console will work with a SECAM console.

 

I do not believe that you will have success if you simply try to use an RF modulator from a VCR, Genesis or some other kind of equipment.

 

Atari 2600 cartridges for PAL and SECAM regions are the same - cartridges are region specific with regard to NTSC or PAL, but the PAL and SECAM television systems are similar enough that the PAL cartridge format works for both systems.

 

Please do not worry about your English - it is better than that of many native speakers already. If you write something that we do not understand, we will simply ask you to rephrase it.

[Paul Sernine]

Hello, thanks for your reply.

 

You´re right, SECAM system only applies to France and it´s former colonies. I live in Spain so I suppose the console was bought across the border.

 

I agree with you, finding a proper replacement for the RF unit would be nearly impossible. I shoud stick to the composite video mod, but haven´t find so far a document explaing how to do this modification on a PAL console.

 

I don´t think the RF modulator is servicable no more, the broken choke is impossible to adjust (the photo may lead to error, it appers to be in better shape than it really is) as the coil is almost gone and the little screw falls apart whenever touched. Adjusting it from the bottom. might be possible but i have to de-solder de unit first, maybe this weekend I find the time to do it.

 

Anyway, I still think my better option is the composite video mod. I´ll keep searching, if anyone has information regarding PAL consoles please follow up.

 

Again, thanks very much for the reply.

Edited July 7, 2006 by Paul Sernine

[Paul Sernine]

Here I go again.

 

Well, i´ve finally found the PAL TIA pin-out (it was right in this forum, by the way).

 

TIA PAL

TIA NTSC

 

My idea is to construct the following circuit, replacing the NTSC TIA pins with it´s corresponding PAL TIA equivalent. I Have LUM0, LUM1, and LUM2 located on pins 7,5 and 6. Also I have CSYNC on pin 2 like in the NTSC version.

 

 

But i´m still needing the chroma signal to feed the circuit, sadly i still don´t know where to get it

at this link i read:

 

The Chroma signal is picked off the board at the junction of C210 and R210. Looking at the board, R210 is the 4th component from the right in the bottom row of resistors/capacitors under the shield. It connects to C210 (5th component from the right) at the top of both components, and this is where to solder the wire for the Chroma circuit.

 

However this doesn´t stand true for my board, I´ve looked for Capatitor 210 and Resistor 210 and they aren´t even near each other.

 

So i´m stuck here, whith no chroma signal.

 

 

My second option, is to construct this other circuit which doesn´t look like it needs chroma to function (i´m a litle puzzled about that):

 

link

 

Luma signals 0,1,2 are fed into the circuit, along with CSYNC and a +5 V signal which, i believe, can be obtained from pin 20 of the TIA (please correct me if wrong).

 

Nevertheless, by following this method I need to crush some of the resistors already in the board in order to make it work. I don´t know which ones need to be removed (becouse my board is totally different) so here i´m stuck again.

 

Basically what i need to know is wether there is a way in which i could locate te chroma signal on my board so I can use method one. Or alternativelly if the second method would work without removing the resistors on the board.

 

Audio it´s a whole different story, i don´t even know where to get it. Does the TIA carry audio too, or is it managed elsewhere?.

 

Again thaks for the help, it´s much appreciated.

[A.J. Franzman]

My idea is to construct the following circuit, replacing the NTSC TIA pins with it´s corresponding PAL TIA equivalent. I Have LUM0, LUM1, and LUM2 located on pins 7,5 and 6. Also I have CSYNC on pin 2 like in the NTSC version.

 

 

But i´m still needing the chroma signal to feed the circuit, sadly i still don´t know where to get it

at this link i read:

 

The Chroma signal is picked off the board at the junction of C210 and R210. Looking at the board, R210 is the 4th component from the right in the bottom row of resistors/capacitors under the shield. It connects to C210 (5th component from the right) at the top of both components, and this is where to solder the wire for the Chroma circuit.

However this doesn´t stand true for my board, I´ve looked for Capatitor 210 and Resistor 210 and they aren´t even near each other.

 

So i´m stuck here, whith no chroma signal.

On the pinout diagrams you found, chroma is called "color", and is pin 9 in both instances. C210 on an NTSC board is the first/only capacitor that connects directly to pin 9, and the junction of C210 and R210 is on the opposite leg of that capacitor from the pin 9 connection. So for your console, it should only take you a minute or so to find the equivalent circuit location.

 

 

My second option, is to construct this other circuit which doesn´t look like it needs chroma to function (i´m a litle puzzled about that):

 

link

 

Luma signals 0,1,2 are fed into the circuit, along with CSYNC and a +5 V signal which, i believe, can be obtained from pin 20 of the TIA (please correct me if wrong).

 

Nevertheless, by following this method I need to crush some of the resistors already in the board in order to make it work. I don´t know which ones need to be removed (becouse my board is totally different) so here i´m stuck again.

This is Benjamin Heckendorn's second version composite mod circuit, which does not work correctly as shown, because he forgot to include the chroma connection. I believe all that is needed for it to work is a wire from the C210/R210 junction (on NTSC consoles only, of course) to the "composite video out" point.

 

 

Basically what i need to know is wether there is a way in which i could locate te chroma signal on my board so I can use method one. Or alternativelly if the second method would work without removing the resistors on the board.

I would not go about "crushing" resistors as Ben advises. Really, if you need to disconnect one, just unsolder one lead and lift it away from the board. Anyway, you might be able to get the first method to work by now. The only things I am unsure of are the two additional pins on the PAL TIA chip, called "PAL-I" (pin 8 ) and "PAL-S" (pin 12) on the pinout diagram. I don't know if these signals are needed to make good PAL (or SECAM) video, and if so, how they should be connected.

 

 

Audio it´s a whole different story, i don´t even know where to get it. Does the TIA carry audio too, or is it managed elsewhere?.

 

Again thaks for the help, it´s much appreciated.

The audio is on pins 12 and 13 of the NTSC TIA chip (connected together immediately on the board), but only pin 13 of the PAL TIA chip. On the NTSC circuit board, this signal goes to a 1k ohm resistor to +5V and a 1 uF capacitor before continuing on to the audio mixer circuitry. The external audio signal can be taken directly from the leg of the 1uF capacitor opposite from where the TIA audio signal comes in. This should be similar on your board, but of course I can't tell you the part number of the 1uF capacitor, so you will have to find it for yourself.

Edited July 9, 2006 by A.J. Franzman

[Paul Sernine]

A.J. Franzman, many many thanks. That´s all i needed to know.

 

I will go for method one. Tomorrow i will be locating the first capacitor coneccted directly to pin 9 of the TIA to use it as input for the chroma signal.

 

Just a silly question more. What would the result be if i take the chroma just directly from pin 9 of the TIA, before it reachs the other side of the capacitor ? just curious about that.

 

If i happen to be the first to make this mod on a SECAM board, i´ll have my work documented for others to follow.

 

I´ll keep you posted.

[A.J. Franzman]

What would the result be if i take the chroma just directly from pin 9 of the TIA, before it reachs the other side of the capacitor ? just curious about that.

The chroma signal level, or chroma DC level, might be too high in the combined signal, causing distortion or no picture.

 

If you're not happy with the result from the capacitor, you can try taking it directly from pin 9 (this should not damage anything), but I would not expect any improvement.

 

If you happen to find out what the "PAL-I" and "PAL-S" signals are, please tell me.

 

Good Luck!

Edited July 10, 2006 by A.J. Franzman

[Paul Sernine]

Ignorant as i am, i´m not even able to identify the TIA chip.

 

I have two 40 pined chips on the board, allow me to introduce them.

 

This one reads: TSU C010444-11D

 

 

And this other one: C010750-12

 

 

I´m asuming that the TIA chip is the second one.

 

Well, i have been following the paths on the circuit board. And this are the results:

 

TIA -------------------------------> Component

______________________________________

Pin 8 (PAL-I) ---------------------> C223 (rightmost side)

Pin 9 (Color) ---------------------> C222 (rightmost side)

Pin 12 (PAL-S) -------------------> C219 (leftmost side)

Pin 13 (AUD-0) ------------------> C218 (leftmost side)

 

In the following pictures, spots marked with the red circle are directly coming from the TIA.

 

 

 

am I wrong or all this capacitors seem to be directly connected to ground on the other side ? I´m unable to follow the path further.

 

Relating to PAL-I and PAL-S, right at this thread I read:

 

I am going to gues that PAL-I and PAL-S are the video clock inputs. On the NTCS machine the video frequency is derived from the main system clock, but since PAL uses a different base video frequency a second clock input is provided so that the CPU/system clock can remain the same as the NTCS version.

 

I´ll keep investigating, just want to be as sure as posible of the soldering spots are correct before going for the soldering iron.

 

Regards.

Edited July 10, 2006 by Paul Sernine

[Paul Sernine]

I´m a bit puzzled right now.

 

You´d probably noticed i have mistaken the TIA, for the RIOT. The part number on the chip gave me the clue, so forget about the pictures above since they are useless.

 

When I gave a second glance at the real TIA chip (TSU C010444-11D) first thing I noticed was that it´s part number was very similar to the NTSC one. Second thing was that pins 12 and 13 were soldered together.

 

Just to be sure, I have connected a RCA cable to pins 13-12, and grouded it to the metal plate (no soldering here, just sticky tape), then plugged the RCA conector on to my TV set, and what did i get ?? SOUND :!:

 

It is correct, it is a NTSC Stella Chip

 

What is it doing on a SECAM board ?, beats me !.

Is this really a SECAM board ? I dunno, only clue I have is the "-S" after the model number. It should be "-P" for PAL or "-N" for NTSC.

 

I´ll keep you posted.

[A.J. Franzman]

Now I'm really sorry I wasn't online yesterday - an NTSC TIA in a SECAM 2600 ?!? Wow!

 

For any others who may be reading along, that's the one with the "CO10444..." part number. The other 40-pin chip is the RIOT (a.k.a. PIA) chip, which has both Atari's part number (CO10750...) and the generic part number (6532) marked on it.

 

To answer your question about the capacitors you found by following tracks from the wrong chip: yes, those are grounded on their opposite ends. Now let's return to the subject we want to discuss-

 

IIRC, you're in a PAL country and using a multistandard TV or monitor, right? In this case, an NTSC video mod should be just what you need - you only need to go back and disregard the PAL TIA pinout, and start over again looking for the correct connection locations using the NTSC pinout. The first option from your original post still seems to be the best way to go.

[Paul Sernine]

Hello again.

 

Sorry for the lack of updates, but I was on vacation.

 

Anyway here I am again with renewed determination to fix the composite video circuit.

 

Yesterday I bought all the required parts and put the circuit together, today i have tested it to discover I get sound, but no video at all

 

 

This is a close up of the circuit, could someone please review this ? I don´t know where the flaw may be. Perhaps the resistor is not in the correct position? the golden band is looking to the output of the circuit.

 

 

I have used the NTSC pin-out as reference, and soldered the cables directly to the TIA chip, (including chroma, as I was unable to follow the track of pin 9 to the first capacitor). The connections are as follows:

 

Black cable ---> Pin 5 (LUM1)

Pink cable ---> Pin 7 (LUM2)

Violet cable ---> Pin 8 (LUM0)

Red cable ---> Pin 2 (CSYNC)

Yellow Cable ---> Pin 9 (COLOR)

White Cable ---> GND (to the metal plate)

Green Cable ---> Pins 12 and 13 (Audio)

 

As you can see, Video signals are joined together just before entering the RCA Cable, The same ground is used for audio and video.

 

As for the potentiometers, i have mounted them acording to this picture:

 

 

Chances are that, inexpert as i am, I made some stupid mistake with the circuit. Otherwise the pin-out of my TIA chip is not like the NTSC one, and i´m left to the "test and error" method to determine the correct location of the LUM pins.

 

Any help will be much appreciated, I need a morale boost right now

[atarimind]

[A.J. Franzman]

Resistors have no polarity; they can be installed in either direction. I can not find any problems with the circuit as shown.