CRT is brighter to one side [Hitachi CTP213]
 

Hi, on my searches for a CRT tv, I came across a TV which is close, and in my price range. There is an issue with the tube where roughly 1/4 of the screen is brighter to one side.

Is this just a "setting" issue (I think its called convergence, I could be wrong?)and needs to be adjusted correct again or something else?

Thanks

Re: CRT is brighter to one side
 

It doesn't look like a convergence issue, in fact it looks like a PIL tube which has no such adjustments, or very few.

Many sets used a 200V supply for the RGB output stages which was rectified from a winding on the lopt usually, or sometimes a winding on the smps transformer, synchronised with the lop stage. In such sets the reservoir capacitor for this supply can dry out causing the 200v to "droop" between flyback pulses... with symptoms exactly as is seen here. So possibly a capacitor fault.

Pete

Re: CRT is brighter to one side
 

So would you say to buy and just test capacitors and replace any which need replacing?

I'm happy to do so, as capacitors aren't too tricky.

Thanks

Re: CRT is brighter to one side
 

Hi,
This would seem a pretty good candidate to me- being Japanese it will probably be more reliable than something British from the same era! I can't tell whether it's a delta tube or a more modern PIL type. The convergence looks spot on to me so it's probably a PIL tube.
The shading, although it's not too obvious from the pictures, is a fault and not an adjustment issue.
The supply to the tube's first anodes will be derived from the line output stage and will have a smoothing electrolytic capacitor. If this has failed it could give this symptom.
It could be a number of other things but should be perfectly fixable. Between the lot of us we should be able to point you in the right direction.
I would say if it's nearby and a sensible price it's probably worth getting, but only you can decide if it's worth a gamble!

Good luck
Nick

Dangerman- you can obviously type faster than me! We are obviously thinking along the same lines though!

Re: CRT is brighter to one side
 

Thank you for your replies. I'll definitely try and get it.

I'm glad I've FINALLY found one!

I'll post an update of whether I get it or not.

Thanks

Re: CRT is brighter to one side
 

You've got to love that vintage ultrasonic remote.

Re: CRT is brighter to one side
 

I'm sure in the past I have found shading to be due to an o/c A1 decoupler but probably on earlier sets than that.

Peter

Re: CRT is brighter to one side
 

Hi,

You'll probably find the offending capacitor is on the CRT base.

In the later Hitachi chassis it was C715, a 4.7uF device which needs to be rated at about 250V, I'd expect it to be similar, if not the same in this set.

Love that remote!

Stu

Re: CRT is brighter to one side
 

Yes, I had a similar problem on an HP XY monitor once, the vector would start off at the correct intensity but just fade out over it`s length, whatever direction it was going in.

Little electrolytic cap on the tube base.

Re: CRT is brighter to one side
 

By sounds of it, it is definitely a capacitor, then! I'll have a look if I get it (I've put interest into it)

I agree about the remote too. I love how basic they are too.

Fingers crossed I get it!

Edit: If I do get it, and need help, is it okay to ask on this thread again?

Thanks for all the replies!

Re: CRT is brighter to one side
 

That capacitor is normally near the loptx and decouples a diode that feeds RGB stages.

Post any further help needed and the cure to help others.

Re: CRT is brighter to one side
 

Not completely sure, but one model had an odd tubular metallic capacitor on the line output transistor's sub-panel which would do this. All the advice above is sound of course, but this might just be that chassis.

Re: CRT is brighter to one side
 

Isn't that the model with 'instavision' which is a feature designed to shorten the life of the tube, with the serendipitous advantage of making it warm up faster?

Re: CRT is brighter to one side
 

I have no idea what tube it has, but I won it, so I can tell you on Thursday, when I go to pick it up if you like, I might be able to see what tube it has and tell you.

Re: CRT is brighter to one side
 

I can't quite see what the three buttons on the remote do.
Perhaps channel up, channel down and off.

At least one set I remember did not allow for switching on again, the off button operated a solenoid that unlatched the power switch in the set, and if you were lucky, the plastic button would be ballistically propelled across the room.

Re: CRT is brighter to one side
 

It’s probably got the same feature as the 2 CFP-470’s that I have, they have a switch on the side to keep the heaters lit all the time, and another power switch coupled with the volume which is really just standby. The Instavision came a bit later, I also have one of those! It just has a really fast heating tube, although I did read somewhere about them possibly being directly heated cathodes, which were short lived. The 2 CFP-470’s have got knackered tubes, probably from living on standby! Other than that they haven’t had any replacement parts! They look like they could do with a service now though, frame linearity is suffering on one and the convergence is a bit of a mess on the other. They have 14” delta CRT’s.

Regards
Lloyd

Re: CRT is brighter to one side
 

Well done- hope you got it for a good price! I had an early Hitachi slightly older than this one, many years ago. In standby, it left the tube heaters running at reduced power. Whilst not good practice, it hadn't done the tube any harm. Amazingly well designed set- nothing like the British stuff I was used to!

When you get it, post some internal pictures and the model number. Someone will be able to come up with a circuit diagram (not a schematic-arrgh) and then we can do some fault finding!

Lloyd- I always found delta tubes rejuvinated really well- they seem to have massive cathodes compared with later PIL types. Have you tried doing yours?

all the best
Nick

Re: CRT is brighter to one side
 

I did give one of them a quick go with the B&K, and it did come up a bit brighter, I only used the clean and balance option rather than nuke it with rejuvenate! I should try the other one now I have a new B&K, the old one developed a fault which made the whole front panel live... guess how I discovered that!

Regards
Lloyd

Re: CRT is brighter to one side
 

I remember a Baird branded set which did this with the power. The other two buttons - one was a volume control which when pressed would set it to roughly half of the current volume setting, pressing it again would restore it to whatever level was set on the pot. The other button was a channel cycle button which would advance it one channel at a time. Not much need for a channel down button when it only had 6 channels :)
I also remember these sets would change channel if you jingled a set of keys in front of it, and one engineer told me that if you pointed these remotes at budgies they'd go crazy and start squawking!

Re: CRT is brighter to one side
 

That sounds like the best set ever made which would be the infamous Fidelity AVS2000 or its smaller 1600 brother;D

If INH sees one of these he'll definitely want one and members will be chafing at the bit to help him fix it - especially John:D