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 G'day Everyone and Kriesler Super fringe schematics
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 Return to top of page · Post #: 31 · Written at 9:37:34 PM on 27 March 2020.
Brad's avatar
 Administrator
 Location: Naremburn, NSW
 Member since 15 November 2005
 Member #: 1
 Postcount: 7290

Photos uploaded to Post 23. Apologies for the delay.


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A valve a day keeps the transistor away...

 
 Return to top of page · Post #: 32 · Written at 10:46:18 PM on 6 August 2021.
BurntOutElectronics's Gravatar
 Location: Melbourne, VIC
 Member since 2 October 2019
 Member #: 2392
 Postcount: 268

Okay, it's been ages since I last played with this TV but the picture is now looking good with nice geometry.

However I've got an issue that seemed to have developed out of the blue. Mind you I really haven't used the TV much over the past year or so, but I've got a spot on the centre of the CRT after switching it off that would normally be associated with a weak crt but that's certainly not the case as I get a very nice picture from this set. However it's a issue to the point where I have to pull the socket off the CRT to avoid burn in on the face. It's a bright spot and it lasts a fair while. It only happens sometimes when I turn it off and not others.

Could it be something to do with the added capacitance of a tripler over the flyback? I can change the intensity of the spot with the brightness control and even have the spot appear through capacitive coupling when the socket to the neck isn't making contact.

Also what can I adjust so the picture pulls in better sharpness before full crystallisation? It's too soft when the fine tuning is where it should be.


 
 Return to top of page · Post #: 33 · Written at 7:43:08 AM on 7 August 2021.
BurntOutElectronics's Gravatar
 Location: Melbourne, VIC
 Member since 2 October 2019
 Member #: 2392
 Postcount: 268

I was wondering if it had something to do with not always having turned it off with the TV's own power switch and alas the service manual states very clearly to not do what I did otherwise you'll get a dot! Looks like I should read up a little first and be less dense


 
 Return to top of page · Post #: 34 · Written at 11:05:01 AM on 7 August 2021.
Robbbert's avatar
 Location: Hill Top, NSW
 Member since 18 September 2015
 Member #: 1801
 Postcount: 2011

TVs have a spot swallower circuit to cut off the tube when you switch it off, to prevent what you saw. I don't know any details of it though.

As for the sharpness, you might need a small tweak of the focus control, which could be mounted on the tube base, or on/near the line output transformer.


 
 Return to top of page · Post #: 35 · Written at 2:03:28 PM on 7 August 2021.
Ian Robertson's Gravatar
 Location: Belrose, NSW
 Member since 31 December 2015
 Member #: 1844
 Postcount: 2363

"Spot swallowers" work either by cutting off the CRT or by turning it to max brightness so the HV is discharged.

Your Kriesler uses a contact on the power switch to achieve the discharge, which results in a bright flash on the screen at the instant of switch-off. There are other designs that don't rely on the power switch method, using a number of clever tricks.

There are pros and cons for both methods.

For the discharge method to work, the CRT must have enough emission to draw the current necessary to discharge the HV completely. This is why a weak CRT will show a spot. In your case, the extra capacitance in the tripler adds to the time it takes to discharge the HV while there is still some scan happening.

Cut-off techniques require a long time constant storage in a capacitor to hold the tube in cutoff long enough for the cathode to cool.

Re the picture sharpness related to the fine tuning, due to thorough adjacent channel trapping that is fairly typical of many Krieslers I've seen and would require a complete vision alignment to improve - special gear needed and whatever you do, DON'T fiddle with a TV's IF alignment!

Since adjacent channels are no longer an issue, sometimes the traps can just be disconnected, resulting in a vision bandwidth improvement.


 
 Return to top of page · Post #: 36 · Written at 7:24:52 AM on 8 August 2021.
Brad's avatar
 Administrator
 Location: Naremburn, NSW
 Member since 15 November 2005
 Member #: 1
 Postcount: 7290

I can't say I've seen a coloured set have the spot on switch off but the black and white set my family had when I was little had one on start and stop.


‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾
A valve a day keeps the transistor away...

 
 Return to top of page · Post #: 37 · Written at 10:00:07 AM on 8 August 2021.
BurntOutElectronics's Gravatar
 Location: Melbourne, VIC
 Member since 2 October 2019
 Member #: 2392
 Postcount: 268

Yeah now you mention it Ian, the crt does get set to full brightness as you turn it off.
I just have to get the channel select knob off which is frozen onto the shaft.
The switch has always felt gummed up so I'll clean it up.

Talking about grease turning to cement, yesterday afternoon I had a old lady drop off a late 70's Philips import transistor radio with am and fm. She needed a new volume knob for it as it's plastic in the knob had snapped so I just grabbed a generic new knob with a brass insert, should outlast the radio was my thinking. Anyway turned out the pot had gone completely stiff and with a bunch of spray and prying at it backwards and forwards with a shifter to finally work out the old grease I got it freed up good. After that I found the FM was totally dead so I found the schematics online, tested voltages on the transistors and found the oscillator/converter transistor had corroded one of its legs which broke upon removal. These were the crappy glob top silicons. Scrounged around and found a exact replacement part! ED1502 transistor it was. So I realigned the oscillator back on frequency and now she will have a well functioning radio once again.


 
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