Commodore 1084 (1081) Monitor problem

[daver2]

I wouldn't go too mad at adjusting things just yet until Hugo has had a chance to comment.

Dave

 

[demonlg]

Ok, seems fine for now but i check the component on the neckboard and have to repair M6 connector, or probably i remove it and solder wire on the board, all the pins of the M6 connector have widened because of me by inserting the leads of the multimeter.

The attached image is the C64, the striped colors you see are due to the C64 which has a problem on the 2114 video color ram.

 

[demonlg]

Changed C64 video RAM......

The little issue now is, if i turn on the monitor and is going to hot the image is ok an retrace lines are not visible, but if turn on for few minutes then the retrace lines appear again and when hot again, abount 20-30 seconds, lines going out and image is ok.

This is a symptoms of a bad resistor or capacitor for me....., not in PSU because all replaced and new and good quality.

 

[daver2]

I think you may need to take a video of what you mean and post it on a public file sharing site. Then post a link to it.

This will help us rather than a description and photograph.

Dave

 

[Hugo Holden]

The main determinant of the beam brightness is the relative voltage between G1 and the cathode, but the first anode G2 voltage will also affect it too, all else equal .

If retrace lines occur, it could be because the beam current is simply going to high and they are not being blanked, that would likely be the case if the whole raster scan was brightening up at the same time the retrace lines became visible.

A video would help.

(we know everything is fine with the H output stage and the flyback transformer and the EHT because of the correct sized raster scan. Flyback transformers are not adjustable, they are designed with a fixed set of parameters)

 

[demonlg]

Ok, i try to make a video tomorrow, now i have to move all in another case because this is with scratch on front, i have another 1084 case in very good condition but without electronics, only the same tube equal of this, but i don't use it.

Hugo, i have a high voltage supports multimeter, upper to 1000v CC and 750v AC, can i measure G1 and G2 with this?

Thanks

Emanuel

 

[daver2]

Yep.

Dave

 

[demonlg]

I have remounted all, in effect the power supply output on 125v rail results at 126.8 volt, i have regulated it at 125v, now when turn on the monitor the GAIN setted previously results lowest..i need to recalibrate it.

Tomorrow continue.

Thanks at all for the moment...

Emanuel

 

[demonlg]

Anyway after complete this 1084 if you don't mind I'll ask you for support for a 1084s-p :D I'll have another discussion if for administrator/moderator is not a problem.

 

[daver2]

Go for it.

I can't guarantee success, but we can have a go. More success guaranteed with Hugo's help of course (especially at the high voltage end of things)...

Dave

 

[demonlg]

Ok, I think that now the 1084 is fine, I completed the regulation of the G2 after having set the 125v binary perfectly, now the defect I described before regarding the retrace lines that appeared when cold has disappeared, now it turns on regularly and you can see very well, I also adjusted the focus. As soon as closed I will post a valid image of the result.

 

[demonlg]

This is the results, have to regulate little vertiical position but.....

Very very thanks at all guys!

Emanuel

 

[daver2]

Excellent news.

Well done.

So, a burnt out protection resistor in this case, and a bit of setting up.

Dave

 

[Hugo Holden]

Go for it.

I can't guarantee success, but we can have a go. More success guaranteed with Hugo's help of course (especially at the high voltage end of things)...

Dave

I have a lot of experience with very high voltages. When I was a boy maybe 13 years old I would visit the local dump (Recycling center now called). I would go through all the junk to find radios, TV's to scavenge parts from, screws, nuts wires etc, as I had no money for any parts. From these parts I would make radios, amplifiers etc. One time on TV, I saw a Plane graveyard in America and dreamed of all the Teflon covered wire, electronic parts, metal fragments etc that I could have scavenged from them to make things.

One of my greatest finds was a defunct Neon sign from a Milk Bar shop. A line transformer made by Jefferson in the USA. It was a large transformer with 15kV a side secondary, the center tap connected to the body of it. I found the 30kV across the two outer terminals very interesting and with some ignition wire connected to it, I could hold the insulated wires, one in each hand and draw out very long arcs of at least a few inches. This is not like 15 kV in a vdu which has a high internal resistance, these line transformers can source a lot of current and is potentially lethal. Then I figured out how to make the Jacobs Ladder, with long pieces of wire brought close together at the base. I made one very tall, at least one meter high, the spark would strike at the bottom and slowly rise to the top, pop gone, and a new one strike at the bottom. With the long wires though, they had a habit of mechanically oscillating. One time I got too close and one of the 15kV wire terminals came into contact with my head, that was an interesting experience.

Still, the electric shock, that shook me up the most, was from a DC/DC converter I made (a Royer oscillator) that converted 12V from a car battery to 400V DC. I was using it to run a 2 foot fluorescent tube in a Hut (like a tree house on the ground) where some teenage neighborhood friends would smoke cigarettes and read those dodgy magazines. But, the tube was reluctant to start, so I would hold one end of it and run my other hand along the glass to start it, but I got connected to both ends and due to the muscle spasm from the DC I could not let go and was stuck connected to it. Very painful. After a while I realized I could make my legs move just a little, I was kneeling, so I shuffled away from the power supply box. Luckily I had just poked the two wires feeding the tube into an Amphenol connector on the box, and it disconnected.

After that, the power supplies that scare me the most are DC ones, anything in the 100v to 1kV region that can source some hundreds of milli-amps or more.

Very high voltage EHT supplies in VDU's don't worry me as much as they are poor at sourcing current and most cannot source over 10 to 30 mA, the CRT's beam current is in the order of 100's of uA, so I generally regard a shock from those as being inconvenient. For most VDU's, you need to worry about the Auxiliary DC supplies from the Flyback transformer, in the range of 100 to 600V DC, when the unit is powered, not so much the EHT supply. Also the rectified line supply on the primary side of the SMPS (if there is one) can be in the range of 300V DC, with a low internal resistance, this is risky. So always be careful to avoid contact with that area too.

 

[demonlg]

Hi hugo, your story is very intresting, i have horror of VDU flyback,
but your story gives me a little more security. Yes, I know very well the voltages of the PSU, sometimes I have mistakenly discharged the 400v primary capacitor, it is painful for a while, I confirm.

The other scary part of the VDUs is the auxiliary DC voltages, that's why I asked yesterday if I could measure with my multimeter.

Finally, I'm always afraid that when I turn on a VDU that has been out for many years it might explode, the cathode ray tube has always scared me and I always will, but many times I've got my hands on it by first unloading and then working, while capacitors are the thing that worries me about my eyes, a few years ago while I was repairing an old IBM 5150 a very small tantalum capacitor exploded and it passed half a centimeter from my eye! From there I decided that when I feed something I do it by moving away.

In the past, and you can also read the discussion in Italian on the arcadeitalia.net forum, I have adapted a 28" cathode ray tube of a TV to an ARCADE electronics, it was a hard job and dangerous for me, but the result is still working today after so many years, I also had to take the datasheet of the CRT, I had to adapt the deflection yoke and the voltages involved.

While just last week I repaired a TRS80 model3 of an acquaintance of mine (mine is perfect) that broke the tube during the trip from the USA, also damaging the flyback by splitting it, luckily I found the piece in Australia, while the deflection yoke I had to remove some coils to be able to re-weld, isolate and replace them, but the result was satisfactory!

I really enjoy repairing these memorabilia, I have many, not enough, some even rare.

I don't have a varistor, it's always something I have to build myself but I never do.

Anyway thanks to these tests I realized that 2 of my 10 C64s have some little problems, one video RAM fixed, and a 64C I hope it's not the PLA that I haven't been able to find for years, that big and evil chip that mother Commodore has invented to reduce the encumbrance of the logics, for me a not insignificant design error.

I reassembled everything and the 1084 is already on my Amiga 1000 in its place, the other 1084P is on the Amiga 2000 and a 1084SP on the Amiga 4000, now I would like to fix that 1084S to match my C128D, also I have a Philips CM8833 (identical electronics of the 1084S) which, even after a long time stopped working, does not seem to want to turn on, but this experience with the 1084 with you makes me think that time has also damaged the optocoupler, to see both because they were put away working 15 years ago but unfortunately in a place that has become damp over time, then move.
Of them I also have brand new flybacks, on the CM8833 I took some components to repair the power supply of this 1084, such as the missing capacitor! There's quite a bit of work to do.

Speaking of EHT Hugo, one question, if a VDU board is turned on without the cathode ray tube, ie empty, with the high voltage headphone free on a wooden table, what do I risk? Could it bow to anything nearby, including me?
Is there a way to bench test voltages and also EHT?

 

[Hugo Holden]

Speaking of EHT Hugo, one question, if a VDU board is turned on without the cathode ray tube, ie empty, with the high voltage headphone free on a wooden table, what do I risk? Could it bow to anything nearby, including me?
Is there a way to bench test voltages and also EHT?

One good thing about the EHT system in VDU's is that over the years, manufacturers drastically improved the insulation, not only of the Flyback transformer body, but also the wire and rubber covered EHT cap. For most VDU repairs, provided you don't go under the EHT cap you remain totally isolated from the EHT supply while its running and also any stored charge in the CRT too with the VDU off. So generally for most VDU repair work, I simply leave it connected. I remove The EHT cap on occasions to change the CRT, completely remove the pcb etc, in most cases I do it after the set is off for a day. Or, If I want to remove the CRT quickly after turn off , I discharge the CRT, I use an EHT probe, that has a 100 Meg Ohm resistor in it, never a direct short. Don't carry a removed CRT anywhere with any charge left in it, in case you contact that with your hand and drop the CRT on the foor. I have received a shock from a partially charged CRT I was carrying, but I knew it wasn't harmful to me and I managed to keep my composure and not drop it.

It is not a good idea to power the pcb with the EHT/anode lead hanging off it without extremely good insulation over the free anode cap, insulating tape won't do it. It needs to be put in a deep thick walled glass jar and taped in there so it can't fall out. If it arcs anywhere it can cause problems / damage.

A way to test a lot of the VDU circuitry with the board on the bench without the CRT, is to deactivate the EHT and H scan by disconnecting the Collector of the horizontal output transistor, or removing the connection to its base, and tying the base to the emitter, so it goes into a non conducting state, killing the production of EHT and auxiliary voltages. In most cases then you can check out all the vertical circuits and H driver circuits with the board powered and not worry about the EHT and auxiliary voltages.

In terms of breaking a CRT, never strike the glass and don't put anything metal against the glass ever, only plastic. I have seen people try to lever off the stuck yoke tabs with metal screwdrivers, very bad only use plastic tools if anything touches the glass. For most VDU's luckily it is a rare event for the bulb/body to implode, or the face-plate to break as these have been made extremely strong to avoid the need for an external implosion screen which many TV's had prior to the 1960's. In most cases for a VDU CRT the neck is the weakest point and it breaks off with minimal flying glass when the VDU gets dropped. Early CRT's though, like those in scopes too, made of thin walled Pyrex type glass are a little more risky for the total implosion event.

PS: If you wanted to bench test the EHT...you need a dummy CRT, you would have to make in insulated container, a 10mm thick walled acrylic box would do it. And mount a clip to securely receive the anode cap. Inside the box you would require a high voltage capacitor at least 500pF to 1000pF, rated to at least 5kV over what you are testing, you would need a 30kV rated cap to do this for most color sets, and a 20kV one for most monochrome sets and an earth wire exiting the box to connect to the chassis common or the negative bus in the H output stage, or the point in the set where the external CRT Aquadag was connected (usually ground not always in some color sets). Such high voltage caps are available from Surplus Sales in Nebraska. This simulates the CRT's bulb capacitance that needs to be there to get an accurate EHT measurement. Then you have a hole in the box side where you could poke in the long TIP of the EHT probe to measure the EHT. I have never had the call to make such a box. It could be possible to make the test box form the capacitor, as the CRT does, by spraying its inner & outer surface with conductive paint, but likely to get the capacitance up, the box would start to end up a similar size to the actual CRT.

 

[KENSA83]

VDU'lardaki EHT sistemiyle ilgili iyi bir şey, yıllar geçtikçe üreticilerin yalnızca Flyback transformatör gövdesinin değil, aynı zamanda tel ve kauçuk kaplı EHT kapağının yalıtımını da büyük ölçüde geliştirmesidir. Çoğu VDU onarımında, EHT kapağının altına girmemeniz koşuluyla, çalışırken EHT kaynağından ve ayrıca VDU kapalıyken CRT'de depolanan şarjdan tamamen izole kalırsınız. Bu nedenle genellikle çoğu VDU onarım işi için onu bağlı bırakıyorum. Bazen CRT'yi değiştirmek, pcb'yi tamamen çıkarmak vb. için EHT kapağını çıkarıyorum, çoğu durumda set bir gün kapalı kaldıktan sonra yapıyorum. Veya, CRT'yi kapattıktan sonra hızlı bir şekilde çıkarmak istersem, CRT'yi boşaltırım, içinde 100 Meg Ohm direnç bulunan bir EHT probu kullanırım, asla doğrudan kısa devre olmaz. Çıkarttığınız CRT'yi, içinde şarj kalmış şekilde herhangi bir yere taşımayın, aksi halde elinizle temas edip CRT'yi yere düşürebilirsiniz. Taşıdığım kısmen yüklü CRT'den şok aldım ama bunun bana zararlı olmadığını biliyordum ve soğukkanlılığımı koruyarak onu düşürmemeyi başardım.

Serbest anot kapağı üzerinde son derece iyi bir yalıtım olmadan EHT/anot ucu asılıyken pcb'ye güç vermek iyi bir fikir değildir, yalıtım bandı bunu yapmayacaktır. Derin, kalın duvarlı bir cam kavanoza konulması ve düşmesin diye oraya bantlanması gerekiyor. Herhangi bir yere yay yapması halinde sorunlara/hasarlara neden olabilir.

CRT olmadan tezgah üzerindeki kartla birçok VDU devresini test etmenin bir yolu, yatay çıkış transistörünün Kolektörünün bağlantısını keserek veya tabanına olan bağlantıyı çıkararak ve tabanı bağlayarak EHT ve H taramasını devre dışı bırakmaktır. yayıcıya, dolayısıyla iletken olmayan bir duruma geçerek EHT ve yardımcı gerilimlerin üretimini durdurur. Çoğu durumda, karta güç verildiğinde tüm dikey devreleri ve H sürücü devrelerini kontrol edebilir ve EHT ve yardımcı voltajlar konusunda endişelenmenize gerek kalmaz.

CRT'yi kırmak açısından, asla cama vurmayın ve camın üzerine asla metal bir şey koymayın, sadece plastik koyun. İnsanların sıkışmış boyunduruk tırnaklarını metal tornavidalarla kaldırmaya çalıştıklarını gördüm, çok kötü, yalnızca cama herhangi bir şey temas ederse plastik aletler kullanın. Neyse ki çoğu VDU için ampulün/gövdenin patlaması veya ön panelin kırılması nadir görülen bir olaydır çünkü bunlar, 1960'lardan önce birçok TV'de bulunan harici bir patlama ekranına olan ihtiyacı ortadan kaldırmak için son derece güçlü yapılmıştır. Çoğu durumda, bir VDU CRT için boyun en zayıf noktadır ve VDU düştüğünde minimum düzeyde uçan camla kırılır. Ancak dürbünlerde olduğu gibi ince duvarlı Pyrex tipi camdan yapılmış ilk CRT'ler, toplam patlama olayı açısından biraz daha risklidir.

Not: EHT'yi deneme testi yapmak istiyorsanız... yapay bir CRT'ye ihtiyacınız vardır, yalıtımlı bir kapta yapmanız gerekir, 10 mm kalınlığında duvarlı bir akrilik kutu bunu yapar. Anot kapağını güvenli bir şekilde almak için bir klips takın. Kutunun içinde, test ettiğiniz değerin üzerinde en az 5kV değerinde, en az 500pF ila 1000pF arasında yüksek voltajlı bir kapasitöre ihtiyacınız olacaktır; çoğu renk seti için bunu yapmak için 30kV'luk bir nominal kapağa ve çoğu monokrom set için 20kV'luk bir kapağa ihtiyacınız olacaktır. ve H çıkış aşamasında şasi ortak veya negatif veriyoluna veya harici CRT Aquadag'ın bağlandığı setteki noktaya bağlanmak için kutudan çıkan bir topraklama kablosu (genellikle bazı renk setlerinde her zaman topraklama olmaz). Bu tür yüksek gerilim kapakları Nebraska'daki Surplus Sales'den temin edilebilir. Bu, doğru bir EHT ölçümü elde etmek için CRT'nin orada olması gereken ampul kapasitansını simüle eder. Daha sonra kutunun yanında, EHT'yi ölçmek için EHT probunun uzun UCUNU sokabileceğiniz bir delik bulunur. Hiç böyle bir kutu yapma çağrısı almadım. CRT'nin yaptığı gibi, iç ve dış yüzeyine iletken boya püskürterek test kutusunun kapasitörden oluşmasını sağlamak mümkün olabilir, ancak muhtemelen kapasitansı artırmak için kutu gerçek boyuta benzer bir boyuta ulaşmaya başlayacaktır. CRT.

Hello Hugo. I'm new to the forum. Can you help me with this?

https://forum.vcfed.org/index.php?threads/commodore-1084p-mono-problem-there-is-sound-there-is-no-image.1247452/