What Diode?

[19Seventy7]

Originally Posted by toshiba tony

Without the diode you have no feed to the RGB output transistors. This should result in a peak white raster, unless the A1's are backed off. And what does CR denote. Please post the section of the manual to aid us all.

I have the diode, not the resistor which is next to it on the board.

I have no raster or anything on the TV when it's on.


CR is the diode - I think.

Hang on, you are the guy who had picture shading, what have you done!!!!!
When you restore your picture you will still have shading, change the RGB HT decoupling cap as well. If you post the relevant part of the manual there are very clued up people on here who will id said component. I had a Hitachi account and all their manuals, now long gone.

Yes that is me.

I changed the capacitors which I was told to. That's when I noticed this problem. I turned the set back on to find no image.

Where is the HT decoupling cap? I don't really know where things are too well. I just know what they are, what they do generally, but not what they do to the set. I have attached a picture from the manual showing CR703 and the surrounding area, if that helps? (I'm using the same manual Lawrence has linked)

Also the diode won't meter like a normal diode, it will read o\c in both directions.

I don't get any reading from the diode at all just "1" which the DMM always shows when on the diode setting.

I'll have a read of that thread now

Thanks

[Station X]

Unless I've got the wrong end of the stick, which is quite likely, the diode has crumbled so there's little point in testing it.

[19Seventy7]

My bad. I made a typo. It should read “the resistor was so burnt out it crumbled in my hand”

The diode looks visually fine.

As for the multimeter. I am not too sure how to use them properly.

However the red pin just fell off the wire today when i picked it up, so im wondering if there was ever a connection. Although it worked when the two pins were pressed against eachother to test.

Thanks

[19Seventy7]

Do you need to remove the diode from the PCB to test it?
I have been testing the diode with it still being in the PCB

Thanks

[Refugee]

I think you had better repair or replace your meter probes before you go any further.

[19Seventy7]

I shall fix them tomorrow as i have no others.

Do i remove the diode before testing?

Thanks

[Refugee]

You should have no problem with the resistor gone.

[19Seventy7]

Oh.

I still get no reading. I think i’ll send the DMM back and get another considering it 1) goves no reading and 2) fell apart.

Thanks

[toshiba tony]

I fully appreciate this forum helps people in many ways, but I think this poor poster must be in a turmoil. It appears originally his A1s were ok. He had shading on the picture which CAN be ripple on the RGB 200v line. Lawrence put us right, the offending component that has met it's demise is the rectifier for the A1s. Now it seems we have a very dull raster, for TV engineers it's a very simple procedure to suss out the issue. But when you are in the dark (pun intended) things can be hard. Another point is these diodes read o\c even when they are ok. I get "engineers in with microwaves saying the diodes clamped to the case are faulty because they read o\c. Well, they do, even when ok. I cannot access the site Lawrence mentioned but if he identifies the A1 diode, its series resistor and the RGB decoupler I reckon we will sort this guy.

[19Seventy7]

I am in turmoil. As ive said before i have very very little knowledge of these. It was even worse when my “fix” made it worse which left me with something i had even less knowledge about.

So if i were to leave the diode for now, presuming it is indeed okay.

I just need to focus my attention on the decoupling cap and the recitfior or resistor?

If you mean the site for the manual I can try link it tomorrow to see if that helps? (I dont have the link on my phone)

Thank you for your help. It is greatly appreciated

[Clydeuk]

V11N appears to still be available, but from the USA. A quick search suggests NTE558 as a sensible equivalent. This appears to be available on eBay here in UK. It appears to be rated at 1500 volts and 1 amp. Because you don't have any scrap chassis to raid it might be sensible to get a diode that matches or exceeds the original spec.

Have to say in my own experience it's rare for a diode of this type to fail open-circuit, though not impossible I guess.

[19Seventy7]

Originally Posted by Clydeuk

V11N appears to still be available, but from the USA. A quick search suggests NTE558 as a sensible equivalent. This appears to be available on eBay here in UK. It appears to be rated at 1500 volts and 1 amp. Because you don't have any scrap chassis to raid it might be sensible to get a diode that matches or exceeds the original spec.

Have to say in my own experience it's rare for a diode of this type to fail open-circuit, though not impossible I guess.

I had seen them, but im not sure i want to pay £10 shipping for something otherwise fairly cheap. I will go with one of the ones reccomended to me, if need be as it may not be the diode at fault after all.

Thank you for your help

[toshiba tony]

You are certainly attracting interest with your set, that's why I fully recommend this forum to people struggling with anything electronic. Whilst not being in the trade as long as some on here my years in the trade are almost 50. Right, so the diode isn't crozzled? The resistor is? Do you know it's value, I think not if it's charred. Lawrence is your guy for that. As I said earlier, the diode is probably OK. Some confusion arose and it was assumed it was the RGB diode that had failed but that would result in an over bright raster. I think we all have a better idea as to which components have failed, but be aware when you restore your raster you will still have the shading. When you ascertain the value of the said resistor and replace it you "may" get your picture back. Have you no idea why it failed, because of where it is in the set it's unlikely to be a safety resistor, but not being terribly familiar with that model who knows. 30 years ago I would say pick up all you can about televisions, but now
I see about one crt a month, but reliability wise they beat LCD hands down, see you tomorrow!

[Red to black]

Ah right so it is the A1/screen diode, the confusion earlier was down to me, as I was under the impression it was the RGB 200v supply that was in trouble, my bad.

[Station X]

Now that replacement diode types for CR703 have been identified I'll close this thread. Discussion can continue in the OP's other thread relating to his TV:-

https://www.vintage-radio.net/forum/...d.php?t=152139

It appears to me that the OP has been attempting to measure the resistance of resistors using his meter's diode test range. Perhaps a sticky thread on how to use a meter is needed. I doubt anyone would read it, but at least it could be linked to when answering queries.