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Coleco Telstar Combat! No Video Repair HELP!


eDoc

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2 hours ago, TheProgrammerIncarnate said:

The amplification transistor *should* be the first thing after the signal comes in. Also, could you get a picture of the circuit board hidden under the back panel? I never got mine removed.

Sure, photo is attached.

F95B0BFD-4A68-44AA-87A6-AC57FA83655E.jpeg

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This is all starting to sound a bit out of my knowledge/skill zone.  I was hoping this would be a simple fix like reflowing solder or a simple part replacement.  I may just put it off until I come across another cheap junker and switch some parts around.

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6 hours ago, eDoc said:

This is all starting to sound a bit out of my knowledge/skill zone.  I was hoping this would be a simple fix like reflowing solder or a simple part replacement.  I may just put it off until I come across another cheap junker and switch some parts around.

Sorry about that. A composite mod should still be pretty simple.

Quote

Is your picture above in "night mode" or is that the remaining issue you're trying to solve?

This isn't night mode, the background appears black instead of grey (or maybe the white areas are "too white".) It actually looked fine when I plugged it into a modern TV. Again, I'm pretty sure this can be fixed with the correct resistor values.

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So, here's a reverse engineering of the RF modulator.  As I figured, not much.  Just a Colpitts oscillator and a diode going through a variable transformer.

 

Adjust the orange set screw to affect the channel frequency, and adjust the white one to affect signal strength.

 

One question about the bad Combat console:  What is the voltage at the junction of C2, R2, C31, and R37?  It's important that this voltage is good whether you use the RF or not, because it's a good indicator of whether the entire system is getting enough.

 

984511053_ScreenShot2019-08-03at4_31_03AM.thumb.png.42497afb9fa3ebcc7440778f8507d314.png

Edited by ChildOfCv
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8 hours ago, TheProgrammerIncarnate said:

Sorry about that. A composite mod should still be pretty simple.

No need to apologize!  You and @ChildOfCv have already helped me out immensely and I’ve already learned a lot from this :)

I guess if this was a wider known system, there would be more info on it but there’s just not that much info out there.  What are you using to amplify your system in the picture?  Did you add something to the board or are you using something already on the board?  I also just don’t want to have to put a lot of money into this system because it has some other issues like the reset button looks corroded and it’s missing one of the internal speakers.  And I obviously haven’t been able to test the joysticks so they may have issues too.

 

28 minutes ago, ChildOfCv said:

One question about the bad Combat console:  What is the voltage at the junction of C2, R2, C31, and R37?  It's important that this voltage is good whether you use the RF or not, because it's a good indicator of whether the entire system is getting enough.

Ok, so on my board I really dont see a single junction point for those 4 resistors (picture attached).  Using my multimeter I put the prongs on the points of R2 and C2 where the yellow arrows are pointing and got 0.6 volts.

11E6E400-2092-49BF-A5EA-2C5BDC9421FE.jpeg

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10 minutes ago, eDoc said:

No need to apologize!  You and @ChildOfCv have already helped me out immensely and I’ve already learned a lot from this :)

I guess if this was a wider known system, there would be more info on it but there’s just not that much info out there.  What are you using to amplify your system in the picture?  Did you add something to the board or are you using something already on the board?  I also just don’t want to have to put a lot of money into this system because it has some other issues like the reset button looks corroded and it’s missing one of the internal speakers.  And I obviously haven’t been able to test the joysticks so they may have issues too.

 

Ok, so on my board I really dont see a single junction point for those 4 resistors (picture attached).  Using my multimeter I put the prongs on the points of R2 and C2 where the yellow arrows are pointing and got 0.6 volts.

11E6E400-2092-49BF-A5EA-2C5BDC9421FE.jpeg

Well more explicitly, the yellow arrow on the right is pointing to one of the good reading points.  Place your red probe there.  Place the black probe on one of the shield clips, or wherever you can get a good ground reading.  What voltage do you read that way?

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14 minutes ago, ChildOfCv said:

Well more explicitly, the yellow arrow on the right is pointing to one of the good reading points.  Place your red probe there.  Place the black probe on one of the shield clips, or wherever you can get a good ground reading.  What voltage do you read that way?

Ah gotcha.  Doing that I get 6.86 volts (using power supply w/ system on)

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3 hours ago, ChildOfCv said:

So, another question:  As seen in TPI's post, there's a trim potentiometer on the upper right edge of the board.  Your picture does not seem to show such a thing.  Do you have one on your board?

 

Also, do you hear sounds when you turn it on and hit reset and manipulate the controls?

Do you mean the small box with the flathead screw adjuster circles in red.  If so, then yes I have it.

 

As far as sound goes, no.  When I plug the system in, the speaker makes a soft pop like it’s on, but no other sound.  It used to when it would show static, but there’s nothing now.

BA3F7755-84E5-4A66-9DDB-E4F8B81400CB.jpeg

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17 hours ago, eDoc said:

Do you mean the small box with the flathead screw adjuster circles in red.  If so, then yes I have it.

 

As far as sound goes, no.  When I plug the system in, the speaker makes a soft pop like it’s on, but no other sound.  It used to when it would show static, but there’s nothing now.

 

Well, no that's a variable transformer.  I mean like the one with the large plastic knob on the bottom that has some kind of epoxy dripped on it to hold it in place.  You can kind of see it under the large bundle of wires in TPI's pictures.

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Well, using a mass of pictures that I could find, I put together a reverse-engineered schematic of the Combat console.  There are probably errors, but at least it brings some things to light.

 

Looks like a bunch of the extra logic is just to give tank B some input in 1-player mode.  Apparently that's not programmed into the game itself.

 

Anyway, we now have a clear look at the signal into the modulator, though I do need to fill in the resistor values.  If someone could create a glare-free image of the PCB (top and bottom) with consistent lighting (and with components bent to reveal their identifiers), that would be spectacular.

Combat.pdf

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6 hours ago, ChildOfCv said:

Well, no that's a variable transformer.  I mean like the one with the large plastic knob on the bottom that has some kind of epoxy dripped on it to hold it in place.  You can kind of see it under the large bundle of wires in TPI's pictures.

Ah, yes, I am missing that from my board.  Although, there’s no evidence of solder there so it’s hard to believe I ever had one on my board unless someone did an exceptional job of cleaning the solder up.

 

I am beginning to suspect the issue is power related or is a bad chip.  I first thought the reason I wasn’t getting sound from the internal speakers was because  the audio signal was first going into the (faulty) RF modulator, then going to the speakers.  And because the modulator was faulty, there would be no audio output from the modulator.  But, according to your (very awesome) schematic, it looks like the speakers are entirely separate from the RF modulator.  Because the speaker makes some noise when I first turn the system on, it seems like it’s getting power.  It seems to me like it’s the chip not outputting any signals across the board.  I’ll reflow the chip’s solder and see if that does anything.

Edited by eDoc
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7 hours ago, eDoc said:

Ah, yes, I am missing that from my board.  Although, there’s no evidence of solder there so it’s hard to believe I ever had one on my board unless someone did an exceptional job of cleaning the solder up.

 

I am beginning to suspect the issue is power related or is a bad chip.  I first thought the reason I wasn’t getting sound from the internal speakers was because  the audio signal was first going into the (faulty) RF modulator, then going to the speakers.  And because the modulator was faulty, there would be no audio output from the modulator.  But, according to your (very awesome) schematic, it looks like the speakers are entirely separate from the RF modulator.  Because the speaker makes some noise when I first turn the system on, it seems like it’s getting power.  It seems to me like it’s the chip not outputting any signals across the board.  I’ll reflow the chip’s solder and see if that does anything.

The 6.8V reading you got says that the power is good, so I don't think that's the issue.

 

Have you already played with the variable transformer in the upper right corner?  That's the heartbeat for the chip, so if it's badly out of adjustment now, it could be why you have a dead system.

 

Of course, since you have to reset the game to start it, you'd have to make an adjustment, then hit reset to see if it makes a difference, then make another adjustment, etc.

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1 hour ago, ChildOfCv said:

The 6.8V reading you got says that the power is good, so I don't think that's the issue.

 

Have you already played with the variable transformer in the upper right corner?  That's the heartbeat for the chip, so if it's badly out of adjustment now, it could be why you have a dead system.

 

Of course, since you have to reset the game to start it, you'd have to make an adjustment, then hit reset to see if it makes a difference, then make another adjustment, etc.

Well, I believe I have a faulty reset button.  I slowly cycled through the entire range of the variable transformer while pressing the reset button and nothing happened.  No flicker of the tv, nothing.  I tried it through both RF and AV cable.  That said, the reset button never seemed to do anything initially when I was getting a flickering signal.  Also, it looks corroded around the top and actually has a broken off prong (it’s only soldered to the board by 1 prong).  I tested its continuity to the chip and that’s fine, so it may just be bad.  (I attached photos to see for your self).

124E1BD1-DDAF-47A2-8BFB-5380344E7DED.jpeg

56543429-54BF-48FA-BDD5-7A7DAC8329A9.jpeg

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1 hour ago, ChildOfCv said:

By the way, for Q6 (the transistor just to the right of the RF modulator and those resistors, near the top), what is the part number?  In looking at the design, I wonder if that's actually a PNP transistor?

Q6 part # reads:

 

MMPS

6531

EBC

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Wait.. they just bridged the reset button with a solder blob?  I'd expect that to hold the system in reset state permanently.  Try removing the switch and all that extra solder, then solder a couple of wires in.  You'd "hit"  the reset button by touching the two wires together for a second.

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9 minutes ago, eDoc said:

Well, I believe I have a faulty reset button.  I slowly cycled through the entire range of the variable transformer while pressing the reset button and nothing happened.  No flicker of the tv, nothing.  I tried it through both RF and AV cable.  That said, the reset button never seemed to do anything initially when I was getting a flickering signal.  Also, it looks corroded around the top and actually has a broken off prong (it’s only soldered to the board by 1 prong).  I tested its continuity to the chip and that’s fine, so it may just be bad.  (I attached photos to see for your self).

Huh, I wonder if someone tried repairing this unit before...

 

Anyway, I'm back home now and can look at my Combat! unit + take pictures if that helps either of you.

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50 minutes ago, TheProgrammerIncarnate said:

Huh, I wonder if someone tried repairing this unit before...

 

Anyway, I'm back home now and can look at my Combat! unit + take pictures if that helps either of you.

Yeah it sure looks like it.

 

Pictures would be very helpful.  Try to arrange the components so that they don't hide other components or their identifiers, and try to keep the wires out of the way.  Also, plenty of diffused lighting would help a lot, far better than camera flashes.

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1 hour ago, ChildOfCv said:

Wait.. they just bridged the reset button with a solder blob?  I'd expect that to hold the system in reset state permanently.  Try removing the switch and all that extra solder, then solder a couple of wires in.  You'd "hit"  the reset button by touching the two wires together for a second.

@ChildOfCv  It’s not perfect, but we have a breakthrough!  I cleaned up the solder, removed reset switch, and soldered wires on there instead.  Plugged in the system, touched the wires and boom!  I got sound in the speaker, sound when I push the fire buttons and I have a visual!  As you suggested, the system was in a continuous state of reset.  This system has definitely been messed with before.

 

The only thing is, I can’t seemed to tune in the signal (i desoldered av cable and i’m back with using RF to test this). I’m making small adjustments with the variable transformer and the orange inductor, but can’t seem to get a clear picture.  The best I get is when game 4 is selected (last pic), but game 1-3 all have bad static.

8CEA6278-5367-4B40-859A-B78B6E09D2A8.jpeg

26AE6765-C041-4366-AFE9-4CFDDFA3EF33.jpeg

001CFBDA-5830-49AF-8EDC-F0A0EAC1C248.jpeg

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Does your multimeter happen to have a frequency mode?  I think the first thing you need to do is make sure the variable transformer in the upper right is correct.  Otherwise it's going to send sync signals at the wrong frequency.  If you can measure the output frequency of the oscillator, you should be able to tune it properly, and then move on to just the RF module.

 

The white tuner in the RF should be for affecting final signal strength, and it may be the reason that the one mode that changes board brightness seems to work better.

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14 minutes ago, ChildOfCv said:

Does your multimeter happen to have a frequency mode?  I think the first thing you need to do is make sure the variable transformer in the upper right is correct.  Otherwise it's going to send sync signals at the wrong frequency.  If you can measure the output frequency of the oscillator, you should be able to tune it properly, and then move on to just the RF module.

 

The white tuner in the RF should be for affecting final signal strength, and it may be the reason that the one mode that changes board brightness seems to work better.

Unfortunately, my multimeter does not measure frequency.  But I kind of have a feel for where the optimal signal for the variable transformer is.  

 

As far as the white inductor goes, I cannot get it to budge inside, so pursuing AV mod might be the best thing, unless there’s a way to bypass the bad inductor like I did with the reset switch.

 

I will try to see if I can get a signal now with AV by resoldering the cable.  I’ll report back the results.

 

 

Edited by eDoc
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2 hours ago, TheProgrammerIncarnate said:

Huh, I wonder if someone tried repairing this unit before...

 

Anyway, I'm back home now and can look at my Combat! unit + take pictures if that helps either of you.

Thanks for offering!  I would also appreciate pictures of your system. 

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46 minutes ago, eDoc said:

Unfortunately, my multimeter does not measure frequency.  But I kind of have a feel for where the optimal signal for the variable transformer is.

Well, one thing to consider for future purchase is an auto-ranging multimeter with frequency mode.  Looks like Amazon has a no-name brand for a reasonable price, that can count up to 20MHz.

https://www.amazon.com/dp/B06ZZG2F2N/ref=cm_sw_em_r_mt_dp_U_.ClsDbA5ZV8ES

 

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