Teleng (Interton clone) very unstable picture

[Spirantho]

Hi,

 

I've been repairing an old Teleng Television Computer System - which is essentially the British version of the Interton, and rather similar to the Emerson Arcadia I believe.

 

Anyhoo, it's very nearly working now, but the one problem I'm not sure how to get rid of - the picture is unstable. That is, the vertical hold goes kablooie when certain colours are prevalent on the screen.

I've twiddled the knob next to the video generation chip (a PE1X, it seems) and can get it stable for some colours, but never all colours.

The top of the display shows the lines at an angle, so instead of:

 

|-----|

 

it's more like

 

/-----/

 

if you see what I mean. After the first 8 or so lines, they're vertical as they should be.

 

As the VSync is held in roughly this area, I'm thinking the two problems could be related.

 

Does anyone have any idea what to try? I've tried replacing all the caps except two - one of which is miles from the PE1X, the other is the main PSU smoothing cap (the large one). I've reflowed most of the solder joints. I've removed the audio from the signal. I'm currently using a 2N3904 on the video modulator input to grab the composite video, but the same happens with RF. Picture quality is mostly good. Certain colours also send the HSync crazy so the numbers of the score become unreadable.

 

What could cause this? Should I try replacing the colour crystal? It's a 8.86MHz crystal.

 

Any help much appreciated! I can get a photo online if it helps.

[Kakaboy]

I have a SECAM PAL Intellivision . I have removed the SECAM adaptation to the motherboard and added composite AV .

I also have an issue with colour but I have a few components missing as a result of the previous SECAM .

One of the components missing is the 8.86Mhz Crystal . I have a Perfect B&W picture but no colour .

 

Did you manage to solve your issue with the crystal ??

 

I cant find a single 8.86Mhz crystal so I will use 2 x 4.43Mhz in parallel .

I will report back and let you know how it went .

[A.J. Franzman]

Putting crystals in parallel or series does not change the value as it would for resistors or capacitors. You need to find the correct frequency crystal.

[simbo]

sounds like a bad coupling capacitor

or the psu isnt so good

ie a hum bar ie a bad resoviour capacitor

 

so every few lines youll get distortion

 

try to take a few pics of the inside and the screen you get..

 

i think replacing a few capacitors it will be aok,,.

Edited January 14, 2011 by simbo

[simbo]

Putting crystals in parallel or series does not change the value as it would for resistors or capacitors. You need to find the correct frequency crystal.

 

 

no this isnt true

you just use a small TTL ic to double the frequency

very easy

so you can use a 4.43 to make 8.86 but you need to use an ic

and the error rate multiplys by 2

so a 1ppm crystal @ 4mhz becomes a 2ppm error at 8.86

so your not right

and that guy has the right idea in essence just didnt describe his idea right i think

 

8.86 is easy to find ten a penny...

Edited January 14, 2011 by simbo

[A.J. Franzman]

Simbo, Kakaboy said nothing about using an IC to double the frequency of a crystal. I know there are other ways to get a different frequency than what a crystal is made for, but to do so would not be a simple "drop in" fix for his problem, and he's obviously not very knowledgeable so having him attempt to make a daughter module to replace the function of his missing crystal is not very helpful advice.

 

Also, Kakaboy, since your post has little to do with Spirantho's topic, by posting about it here we're doing what is known as "hijacking the thread", which is considered extremely rude. And I'm guilty of aiding and abetting. Please post a new topic for your issue and let's start over.

Edited January 16, 2011 by A.J. Franzman

[simbo]

as i sayed 8.86 mhz crystal's are ten a penny

 

you will find one in just about any tv or video recorder scrap

 

hunt the streets

 

moreover any crystal will resonate at its overtone instead of its fundemental

 

provided you load it right to make it so

Edited January 17, 2011 by simbo

[Kakaboy]

Ok just to update :

 

I have found the right 8.86Mhz Crystal and it didnt work . So I put in a standard 4.43Mhz which is usually used here in AUSTRALIA for PAL . and it worked !!

 

I wasnt too sure what size at first as the only SCematics I could find was for a US version .US INTV has a 7.15MHz Crystal which led me to believe the equivelant in PAL .

 

These are the components I had missing :

 

This is the SECAM board I removed which has the RF :

 

This is the AV mod I used from GAMEX :

 

This is the result :

 

Thanks for replying BTW , appreciate your help .

Edited January 19, 2011 by Kakaboy

[Kakaboy]

I wanted to add to the above post but site wouldnt let me edit ???

 

Just for some extra info to reverse engineer the SECAM adaptation back to the orignal PAL board I had to resolder some cut traces and remove wiring on the back of the board . The crystal was also removed due to the SECAM RF video .

 

Strange thing is they were done post factory on PAL INTV's . There are resistors and caps that are clearly cut . I guess there wasnt enough demand for the Mattel factory to make SECAM INTV's .