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B&W TV USA TV monitors used in very early Pong game

 
AlanJ
(@alanj)
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Hi, I am new here, my thing is really Pinball machines.  A fried acquired two very early and historically important Arcade games.  Nutting Associates "Computer Space Ball" - these are the very first Atari Pong Clone, but the history goes Deeper than that: Nolan Bushnell who founded Atari worked with Nutting Associates and they produced the very first Commercial Arcade game - "Computer Space" - it was too complicated for players so flopped, hence the next idea for Pong - a very easy game to understand.  It was offered to Nutting but they didn't want to make Bushnell a shareholder (as he demanded), so he went off and formed atari instead.  It seems Nutting already had the pong plans from him, because their version came out very soon after Atari's.  Who knows.  Anyhow...

Pics below.

Both "monitors" are actually off the shelf 15" valve b&w tvs - General Electric. I have the schematics for these.   (I used to fix up valve tvs as a kid, but that was over 40 years ago).   

As these games are almost museum pieces, I want to restore using as many original components as possible. So first attempt is to see if I can get these tv's working. 

There is an external power resistor mounted on a board externally - looks like its in series with the heater elements for the valves and crt.   CRT looks in good condition.    The insulation on the EHT coil on both units is nasty, cracking and corroded.   The diode valve that is connected to the EHT section is broken on both TV's - one the pins have corroded off and the other the heater element is open circuit - I have ordered spares - awaiting arrival.

The tuner section of the tv is bypassed with the video signal from the game card wired into the circuit board. Same with the audio.

I have 'dry' tested as best I can the other components - all other valves and CRT heating elements are good. Large tin capacitor seems ok. I guess some of the other smaller caps will need replacing.  Worried about the EHT or LOPT - not sure what terminology I should be using here?

Any advice greatly appreciated.

Also - this is an NTSC std TV - so I presume I cannot sub in a UK PAL unit (if I could find a 15" B&W tv that is!).

Last pic is the gamce circuit board.  Amazingly it uses 66 TTL logic chips to run the game - no microcomputer.  this thing was made in 1972, too early for them.

Many thanks,

Alan

 

IMG 9487a
IMG 9485a
IMG 9505a
IMG 9516a
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Topic starter Posted : 29/06/2021 9:08 am
mfd70
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I guess this TV can be quite easily brought back to life, if you haven't already, take a look a shango066 videos on youtube, old sixties - seventies tube (valve) sets are his speciality and he gets a picture on almost all of them.

I guess there is a power transformer in the cabinet as these sets would need a 110V supply, but most PAL spec TV's would lock at NTSC line rate with maybe a slight adjustment of line hold control, but it would be better to keep it original. If it were mine I'd bring it up slowly on a variac with the line output valve disconnected keeping an eye out for smoke or overheating components then after a couple of hours, refit the line output valve and it may just come to life if you are lucky, else it will need a logical fault finding approach, however black and white TV's are really quite simple especially as the tuner and IF strip are all bypassed. The main issue may well be the CRT, especially it the unit has been used a lot, the emission may be low or the screen phosphor too badly burned, either of which would be "game over" ! See if you can buy or borrow a CRT tester.

It looks a very interesting project though, let us know how you get on.

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Posted : 29/06/2021 12:15 pm
AlanJ liked
Nuvistor
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There is what looks like a Compactron valve in the bottom right of the PCB, appears to have be white mica support for the elements, hope it’s not gone to air and it is mica. There is a valve under the CRT that appears to be milky white where the getter usually is, has that gone to air?

 

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Posted : 29/06/2021 1:08 pm
AlanJ liked
mfd70
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@nuvistor Some compactrons have a side getter, hopefully that's the case here, however US TV valves (tubes) are readily available on-line if rather expensive to post here from the states.

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Posted : 29/06/2021 2:33 pm
AlanJ liked
AlanJ
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Posted by: @nuvistor

There is what looks like a Compactron valve in the bottom right of the PCB, appears to have be white mica support for the elements, hope it’s not gone to air and it is mica. There is a valve under the CRT that appears to be milky white where the getter usually is, has that gone to air?

 

The one on the right is dead, replacement on the way from USA.  Not sure yet about the other one, but checked the other chassis, and that one looks better, so I may have a good one out of 2.

 

 

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Topic starter Posted : 29/06/2021 7:20 pm
AlanJ
(@alanj)
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Posted by: @mfd70

I guess this TV can be quite easily brought back to life, if you haven't already, take a look a shango066 videos on youtube, old sixties - seventies tube (valve) sets are his speciality and he gets a picture on almost all of them.

I guess there is a power transformer in the cabinet as these sets would need a 110V supply, but most PAL spec TV's would lock at NTSC line rate with maybe a slight adjustment of line hold control, but it would be better to keep it original. If it were mine I'd bring it up slowly on a variac with the line output valve disconnected keeping an eye out for smoke or overheating components then after a couple of hours, refit the line output valve and it may just come to life if you are lucky, else it will need a logical fault finding approach, however black and white TV's are really quite simple especially as the tuner and IF strip are all bypassed. The main issue may well be the CRT, especially it the unit has been used a lot, the emission may be low or the screen phosphor too badly burned, either of which would be "game over" ! See if you can buy or borrow a CRT tester.

It looks a very interesting project though, let us know how you get on.

Thanks for this.  Yes the power is dropped to 120v A/c by a transformer to power the TV, it also goes to another power supply transformer and rectifier/stabiliser to give 5v for the "Logic" pcb.    All those test out fine.

If I disconnect the line output valve, I guess I need to bridge the heater pins with a suitable resistor to complete the heater circuit. 

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Topic starter Posted : 29/06/2021 7:22 pm
mfd70
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@alanj You would have to complete the heater circuit if it is a series string set. Do you know what the chassis of the TV is ? It the valve has a top cap you could just remove this.

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Posted : 29/06/2021 8:41 pm
AlanJ
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Posted by: @mfd70

@alanj You would have to complete the heater circuit if it is a series string set. Do you know what the chassis of the TV is ? It the valve has a top cap you could just remove this.

thanks, yes heaters in series.  Its a general electric 15SF chassis.  Here is schematics:

IMG 9499

 

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Topic starter Posted : 29/06/2021 9:36 pm
irob2345
(@irob2345)
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@alanj 

Have a look at this site, there is an article 6th from the end of the list:

https://www.worldphaco.com/

and in this issue:

https://www.siliconchip.com.au/Issue/2021/June

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Posted : 30/06/2021 11:30 am
AlanJ liked
mfd70
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That is a very neat and simple TV circuit, I would imagine the video from the logic board is fed in around TP3 to the video output valve. The set is a US "hot chassis" type with neutral connected to the chassis and half wave rectification, so there must be a mains transformer for isolation as well as step down to 110v. The line output pentode is combined with the efficiency diode (damper) in the same envelope, which I've not seen before. Further to my suggestion of a slow reform of the capacitors using a variac, it would be worth checking the line oscillator which is all transistor, is producing line drive and the coupling capacitor is good before fitting the line output valve, it looks like it would be powered even if the heater chain is open. A check with a 'scope would be best if you have one, as long as the line oscillator is running and the LOPT (flyback) and yoke are good you should get some high voltage in which case you are almost there.

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Posted : 30/06/2021 2:32 pm
AlanJ liked
AlanJ
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@mfd70  Yes the video is going into TP3. And yes there is a step down isolation transformer from 240 to 110v - that all works ok. 

 

Yes, I take your advice on the transistor line oscillator circuit - I can check those points.   I need to get better access to the bottom of the board, the wires to the yoke are quite short, as are other flying wires. I may need to desolder a few so I can get to the board better.  I have an oscilloscope and a meter so should be able to test the circuit out.

 

thank you for looking over the circuit diagram, I really appreciate someone who has experience looking over this for me.

 

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Topic starter Posted : 02/07/2021 3:10 pm