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Old 28th Jan 2019, 6:56 pm   #161
19Seventy7
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Default Re: CRT is brighter to one side [Hitachi CTP213]

Maybe these photos could help?

Edit: 2nd image is location D7
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Old 28th Jan 2019, 7:07 pm   #162
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Default Re: CRT is brighter to one side [Hitachi CTP213]

I deleted a post in error....here it is again:

Quote:
Originally Posted by InsertNameHere View Post
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 mistake.

Okay, do you know which A1 it would be from the list (See attached) as there are multiple.
……...Look at the document header! A1 is the location square on the schematic....

I've already pointed out what diode is what so far as CR703 (the subject of the diode thread) is concerned...…(location square D7 on the schematic)

EDIT: Post crossed.

Lawrence.
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Old 28th Jan 2019, 7:15 pm   #163
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Default Re: CRT is brighter to one side [Hitachi CTP213]

Quote:
Originally Posted by InsertNameHere View Post
Oh my mistake, I just get a little confused at times.

I don't know how to read schematics very well, I just find them useful for finding parts on the board more than anything.

My guess that diode could be CR092 or CR093? i could be very wrong.

Thanks.

You're not the only one who's confused. Me too. CR092 and CR093 are in the tuner and I can't see how they can be anything to do with your fault.

The other thread was about CR703 part of the 800V supply to the screen potentiometer.

Now we're talking about a 200V supply. Is there more than one diode which needs replacing?

Perhaps someone more knowledgeable than myself could sum up this lengthy thread?
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Old 28th Jan 2019, 7:30 pm   #164
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Default Re: CRT is brighter to one side [Hitachi CTP213]

Sorry, just shows how bad I am at reading schematics...

There is a chance that the diode is okay, and that the decoupling cap needs replacing, but i don't know what cap that is.

Thanks
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Old 28th Jan 2019, 7:37 pm   #165
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Default Re: CRT is brighter to one side [Hitachi CTP213]

Quote:
Originally Posted by Station X View Post
You're not the only one who's confused. Me too. CR092 and CR093 are in the tuner and I can't see how they can be anything to do with your fault.

The other thread was about CR703 part of the 800V supply.

Now we're talking about a 200V supply. Is there more than one diode which needs replacing?

Perhaps someone more knowledgeable than myself could sum up this lengthy thread?
The problem was someone mentioned the term A1 (first anode aka the screen)

In the schematic it's referred to as the screen only, A1 ref pertains to the grid square location on the schematic, as a consequence those diodes (A1 grid square ref.) have nothing at all to do with the current problem, there is also an error in the A1 locations for those diodes in the OP's parts snippet because two of those diodes are in fact in grid square A2, not that that affects anything at the moment.

Lawrence.
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Old 28th Jan 2019, 7:45 pm   #166
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Default Re: CRT is brighter to one side [Hitachi CTP213]

Thanks Lawrence.

As I understand it CR703 can't be tested as good as it'll measure open circuit both ways. Obviously if it tests short-circuit it's faulty.
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Old 28th Jan 2019, 8:33 pm   #167
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Default Re: CRT is brighter to one side [Hitachi CTP213]

I have a slight off-topic question.

Why does my DMM always read "1" to the left hand side of the screen. even when trying to test the diode, it just reads 1.

It shows 1 when the probes aren't touching, but when i connect the probes, the screen changes to 001 to the RH side of the screen.

Thanks
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Old 28th Jan 2019, 8:39 pm   #168
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Default Re: CRT is brighter to one side [Hitachi CTP213]

RTFM

"1" is your meter's way of showing that the measured value is out of range. ie infinite resistance or open circuit.

Touching the probes together is not a valid test on the diode test range.

Try testing a good semiconductor diode. It'll read forward volt drop one way and reverse resistance (generally infinite) the other.
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Old 28th Jan 2019, 8:41 pm   #169
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Default Re: CRT is brighter to one side [Hitachi CTP213]

Oh, so that means the diode is okay then, if measuring O/C?

Thanks
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Old 28th Jan 2019, 8:46 pm   #170
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Default Re: CRT is brighter to one side [Hitachi CTP213]

As I understand it CR703 is a special type of diode and an O/C reading both ways indicates that it MAY be good. If it reads short-circuit it's definitely faulty.
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Old 28th Jan 2019, 8:47 pm   #171
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Default Re: CRT is brighter to one side [Hitachi CTP213]

Oh right, i see.

Thank you
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Old 28th Jan 2019, 9:12 pm   #172
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Default Re: CRT is brighter to one side [Hitachi CTP213]

The diode test functions by attempting to pass a small current through the diode, and displaying the voltage that appears across it as a result. So, when the probes are disconnected, or connected to a reverse-biased diode, or a diode with more than around 2V of forward drop at the test current, the meter's internal current source will raise the voltage across the probes above the full-scale reading and the display will show the out-of-range indication. On my meter that is shown as 'OL', on yours it's 1.

Try a dozen different diodes out of circuit, large and small, forward and reverse, to get a feel for normal readings.
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Old 28th Jan 2019, 9:33 pm   #173
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Default Re: CRT is brighter to one side [Hitachi CTP213]

Oh that makes much more sense now, I thought mine might have been a little faulty.

Thanks
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Old 30th Jan 2019, 10:59 am   #174
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Default Re: CRT is brighter to one side [Hitachi CTP213]

The last thing I want to do is kill off any enthusiasm and interest in the repair of old television receivers, especially by the younger generation.
161 helpful replies and we are no further forward, if anything a worse situation.
We need to kill the dragon!

Do you drive? If not,do you have a mate with transport who is willing to spend a few hours to bring this Hitachi over to my workshop in W. Sussex? We can go through it and hopefully get a result.

You need to understand circuit diagrams. Failing this you have no real hope of getting this working and I fear may cause more problems. You need to obtain some old radio BOOKS to do this and study them. They cost practically nothing at radio table top sales, auctions etc.

I'm about 10 miles south of Box Hill Dorking in an area of outstanding beauty so it will be a pleasant journey once off the A3.

Please don't suggest sending it!! A personal visit is essential. The offer is on the table, FOC. Regards, John.
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Old 30th Jan 2019, 2:55 pm   #175
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Default Re: CRT is brighter to one side [Hitachi CTP213]

Fair play John, that's a very generous offer you've made there. I do hope INH takes you up on your offer, having watched you in person working on old sets at Mikey's place, it will be back up and running in no time.

There is no substitute for one to one tuition.

Kind regards,
John Joe.
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Old 30th Jan 2019, 7:10 pm   #176
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Default Re: CRT is brighter to one side [Hitachi CTP213]

Quote:
Originally Posted by Heatercathodeshort View Post
I'm about 10 miles south of Box Hill Dorking in an area of outstanding beauty so it will be a pleasant journey once off the A3.

Please don't suggest sending it!! A personal visit is essential. The offer is on the table, FOC. Regards, John.

Hi John, what a super offer in the spirit of good will!!

INH, (we don't yet know your name?)
I would personally take John up on this offer, I have been to Johns myself before and also seen him work on many sets at "get togethers" at another pals place, his methods and experience are second to none, I can pretty much guarantee that you will end up with a fault free working set and that you will also have a super day whilst learning a trick or two from a very knowledgeable ex TV serviceman!!

Cheers
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Old 30th Jan 2019, 10:47 pm   #177
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Default Re: CRT is brighter to one side [Hitachi CTP213]

Thank you so much for the offer, I don't drive, and the only people I do know who do are my parents. I will ask after responding, and report back.

I don't really understand diagrams and schematics too well. I have been on the look out for books, but the one's I have seen are mainly 1950s, which means it'll be for 405 line sets, which at the moment, I don't think would be too useful for me? I could be wrong.

I really do hope I will be able to take up Johns offer, I couldn't be more thankful for the offer!

Also, my name is Aaron

Thank you again john for the offer, as I said, I couldn't be more thankful!

Thanks
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Old 31st Jan 2019, 11:02 am   #178
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Default Re: CRT is brighter to one side [Hitachi CTP213]

Your very welcome. Can we have a name? It's a friendly forum so no problems.
Books on 405 television are fine for valve TV's. The circuit diagrams use the same symbols.
Your parents are welcome. I'l leave it to you. Regards, John.
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Old 31st Jan 2019, 2:18 pm   #179
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Default Re: CRT is brighter to one side [Hitachi CTP213]

Thank you, my name is Aaron.

If i see any books on 405 line, ill pick them up if i can from now on, they might come in handy at some point.

I think I can come, but may possibly be later febraury, if that is okay?
My dad said he can but not for a little while.

Thank you again
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Old 31st Jan 2019, 2:33 pm   #180
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Default Re: CRT is brighter to one side [Hitachi CTP213]

For books I learnt a lot from Servicing TV and Video Equipment by Eugene Trundle. Although a it was too technical at the time when I bought it, as the years have gone by and my knowledge increased I've found it very useful. You can still buy the book from Amazon.
https://www.amazon.co.uk/Servicing-T...ideo+equipment
It might be worth checking in your local library. Mine used to keep servicing books like this but the reference section is not what it used to be!
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