NBTV Television Analyst

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Re: NBTV Television Analyst

Postby Steve Anderson » Tue Jun 16, 2020 2:01 pm

Proceed one stage at a time...unplug the transformer secondaries - so they are not feeding the power supply rectifiers etc.. If it doesn't blow the fuse check anyway the output of each winding - they'll be higher than usual due to having no load.

If that's OK, plug the transformer output into the power supply board and disconnect all outputs from it - measure the DC output voltages...again they may be a bit high due to no load - if no fuse blow leave it on several minutes, recheck.

If still OK, the next suspect is the EHT generator. There's a link shown between the +12V supply and the EHT generator (W801/P801), remove it. One-by-one plug everything else in. If that's the last thing unpowered it's probably the culprit. Ah! It appears W801/P801 are part of a multipole connector, so that suggestion might be not so easy...

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Re: NBTV Television Analyst

Postby Harry Dalek » Tue Jun 16, 2020 10:46 pm

Steve Anderson wrote:Proceed one stage at a time...unplug the transformer secondaries - so they are not feeding the power supply rectifiers etc.. If it doesn't blow the fuse check anyway the output of each winding - they'll be higher than usual due to having no load.

If that's OK, plug the transformer output into the power supply board and disconnect all outputs from it - measure the DC output voltages...again they may be a bit high due to no load - if no fuse blow leave it on several minutes, recheck.

If still OK, the next suspect is the EHT generator. There's a link shown between the +12V supply and the EHT generator (W801/P801), remove it. One-by-one plug everything else in. If that's the last thing unpowered it's probably the culprit. Ah! It appears W801/P801 are part of a multipole connector, so that suggestion might be not so easy...

Steve A.


Thanks Steve i will have time either late tomorrow or Thursday to sit down and look into to whats up i will for sure listen to your advice here and follow this procedure ,sort of lucky to find this much of the schematic not much out there on the scopes circuits .
My luck it will end up being some thing hard ..i will study the circuit and also look for any burnt parts ...came out of the blue never had a problem with it till now .
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Re: NBTV Television Analyst

Postby Steve Anderson » Wed Jun 17, 2020 1:38 pm

Harry Dalek wrote: ...came out of the blue never had a problem with it till now .

In most cases the power supply is the highly stressed part of any device, in this rather special case it's probably the EHT inverter. But take it step by step and you'll find the culprit in time. Finding replacements or substitutes in critical parts is always harder than the diagnosis.

I hope it isn't the EHT supply, the low voltage power supply would be easy to find spares...

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Re: NBTV Television Analyst

Postby Harry Dalek » Wed Jun 17, 2020 4:16 pm

Steve Anderson wrote:
Harry Dalek wrote: ...came out of the blue never had a problem with it till now .

In most cases the power supply is the highly stressed part of any device, in this rather special case it's probably the EHT inverter. But take it step by step and you'll find the culprit in time. Finding replacements or substitutes in critical parts is always harder than the diagnosis.

I hope it isn't the EHT supply, the low voltage power supply would be easy to find spares...

Steve A.


Hi Steve i am pretty lucky from a mistake i went looking this afternoon and the first plug i removed shown below stopped the fuse from blowing i was mistaking it for one coming from the transformer looking again i can see its powering the CRT from this board .

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Then i plugged it back in to double check and was surprised what the hell its working ...i think perhaps one of the plug connections here might of been just slightly touching its pin may be sparking but it seems fine now which is great the removal and plugging it back in is a very easy fix ! might get a life time out of this scope !
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Last edited by Harry Dalek on Thu Jun 18, 2020 3:11 pm, edited 1 time in total.
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Re: NBTV Television Analyst

Postby Steve Anderson » Thu Jun 18, 2020 11:42 am

It's wonderful when fixes are as easy as that! Unplugging and plugging in again on all internal connectors is assumed before anything else is done. Take the cover(s) off, unplug, re-plug, try again. If it works treat yourself to a beer!

Most failures are related to electo-mechanical components, switches, connectors, pots, relays, anything with moving parts...especially if the unit is quite old and/or stored in a dusty/damp atmosphere...but that's not the case here it seems.

Fuses often 'tire' with age, replace them before even reaching for a screwdriver...those that are externally accessible anyway. but look for any internal ones and replace. You may as well do it anyway while you've got the cover(s) off.

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Re: NBTV Television Analyst

Postby Harry Dalek » Thu Jun 18, 2020 3:58 pm

Steve Anderson wrote:It's wonderful when fixes are as easy as that! Unplugging and plugging in again on all internal connectors is assumed before anything else is done. Take the cover(s) off, unplug, re-plug, try again. If it works treat yourself to a beer!


Well as suggested it seems to work had it going most of the day as well just to make sure no tarnish and no fuse going ...thank goodness yes very lucky ! .



Most failures are related to electo-mechanical components, switches, connectors, pots, relays, anything with moving parts...especially if the unit is quite old and/or stored in a dusty/damp atmosphere...but that's not the case here it seems.


It was not to bad dusty inside for around 30 years ,lucky also the panel switches controls are still quite fine ,i try to keep it clean the places i use it . when the fuse first went i had a hell of a time trying to find it ended up being in a little hidden panel on the power supply plug .

Fuses often 'tire' with age, replace them before even reaching for a screwdriver...those that are externally accessible anyway. but look for any internal ones and replace. You may as well do it anyway while you've got the cover(s) off.

Steve A.


As far as i can see that is the one and only and boy i went looking every where ...when it happened i tried 3 fuses in the fuse holder before taking on your advice with the plugs .

Least i can get back to the project here i am slowing powering the FSS side increasing the HV negative voltage so far every thing looks good no sparking and 75 volt zener still ok now i want to get it up to around bit over 1kv which it was working at in the old trio scope ...i pretty much replaced all the zeners the diode and the transistor and opto just in case ...and its a dead copy of the monitors side which is working fine at 1.4kv up to 1.5kv ,see how the FSS CRT go's tomorrow .....I had to do some other work today which has taken me away from it .
The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Re: NBTV Television Analyst

Postby Steve Anderson » Thu Jun 18, 2020 4:52 pm

OK, good news, you're back in business...

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Re: NBTV Television Analyst

Postby Harry Dalek » Thu Jun 18, 2020 10:14 pm

Steve Anderson wrote:OK, good news, you're back in business...

Steve A.


Yes Steve thumbs up on that for sure :)

I thought i would of finished this by now but short cuts don't always get you there quicker as in picking the wrong FSS tube and going with one deflection amplifier ..its more here lets see if i can do it so its important to try and do your best with what you got ..Once i have a correct sided raster on the FSS CRT rest will go quicker .
The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Re: NBTV Television Analyst

Postby Harry Dalek » Fri Jun 26, 2020 8:51 pm

Well i have been Stalled again on the project ..My scope again out of the blue blew a fuse again after days of working fine using it all day thinking it was the same problem tried the same fix this time no good next disconnected both transformer secondary high low Ac plugs from the circuit boards it was still blowing the fuse and this time smelling that dreadful shorted transformer winding smell it seems the problem if related or not to the last problem this time it is the transformer that is faulty not an easy fix ..
Checking the second scope its vertical deflection seems out so no deflection movement here input or deflection trace movement ...down to the old 80s scope or the the old valve scope arrrrrr looks like i will have to look into the scope problems for now .

Apart from that i also been having problems also with the second FSS deflection circuit for a clean ramp as far as distortion in the frame ramp ...its fine in as i know what you put in is what you get out ....if i was fussy here i would say there's a slight roundness to the frame ramp in ..pretty much a copy out of the ramp generator for the 3bp1 monitor here not causing a problem for its deflection amplifier ..... FSS but after the deflection amplifier its ramp isn't fine i changed all the transistors the balancing between deflection amplifier voltages is not good but the resistors used tested on the collectors are pretty equal first time i have used 1 watt 180k resistors i tended to use in the past what ever i had handy to get this value and resistor wattage ..any case ...back to the scope problem before i can move forward since i don't have a spare transformer ...
But looking on the schematic on page 15 here the AC power its all marked whats what apart from whats feeding the cathode Ac voltage wise suppose you could do a ac power supply via a few transformers the supply for the cathode is not marked pity only one .
i will have to look into whats up on the deflection on the second scope as well ////EDit ...now next day i have looked into this seems ok now fixed looked to be a loose regulator not bolted tight to the case ,that's all i could find i have now vertical deflection on both traces but the time div switch control is limited ,i think some one has done some thing to it before i got it ...got to find the schematic .Any case i will try it on the project today ....thats the best it will do on time div ...better than nothing at the moment
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i wish i could do this on the other scope amazing fix always impressed with those that can make or fix their transformers

youtu.be/ZVSbt5q0KF8

I did btw manage to work out a way to use the deflection for both crts again with resistors and caps but again the FSS crt was not perfect and i am a fussy bugger here .
The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Re: NBTV Television Analyst

Postby Harry Dalek » Sat Jun 27, 2020 1:19 pm

OK scope not greatest but least i can view something...this below is my FSS ramp generator and deflection board.

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The outputs of the DAC size control transistors waveform look good on the frame and line
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I can't really adjust the time div better with this scope on these lower frequencies as i think the scope has been played with around this control switch least at the moment better than nothing .

i had to use my high voltage probe to drop the signal levels out of the deflection amplifiers here below is out of the frame deflection amplifier ramp is a touch wavy ..thinking about it the hv positive might need higher cap but using 220uf 400v should be fine it is for the same supply for the 3bp1 deflection amplifier its deflection ramp is clean ...
The FSS deflection plates need much less voltage to deflect ,i will look into that ...
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DSCN6724.JPG
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The line ramp out of the deflection amplifier best i can show below
DSCN6731.JPG
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The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Re: NBTV Television Analyst

Postby Steve Anderson » Sat Jun 27, 2020 1:44 pm

What a headache! Very unusual for a transformer to fail on its own, usually the result of an overload or damp storage, but if it's smelling of the usual burning transformer smell, it's toast - whatever caused it.

The 'wobbly' line ramp - check the pin numbers are correct between the 4040 and the DAC-08. The slower ramp looks wrong too, it should be a perfectly straight sloping line - did you have the 'scope on AC coupled input? It needs to be DC coupled at these low frequencies...where in the circuit did you measure these waveforms?

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Re: NBTV Television Analyst

Postby Harry Dalek » Sat Jun 27, 2020 5:55 pm

Steve Anderson wrote:What a headache! Very unusual for a transformer to fail on its own, usually the result of an overload or damp storage, but if it's smelling of the usual burning transformer smell, it's toast - whatever caused it.


It was fine last few days unexpected but its the transformer alright i will do a conductivity test onit something must be shorting init you can also hear a buzzing from it ,i have all the information on the secondaries bar one ! the voltage going to the cathode side from that schematic on page 15 posting ..i could make a ac supply box at worst with a few transformers....i will have a think about that one ..

The 'wobbly' line ramp - check the pin numbers are correct between the 4040 and the DAC-08.


I will double check this ,i recall i have before but i will check this again


The slower ramp looks wrong too, it should be a perfectly straight sloping line - did you have the 'scope on AC coupled input? It needs to be DC coupled at these low frequencies...where in the circuit did you measure these waveforms?

Steve A.


I just looked yes i had left it on AC for both traces i will redo these tests tomorrow Thanks Steve

Edit ...next day now
Once again unable to work on the project second scope is not cooperating again today again arrr :x going to bite the bullet and get a desktop digital scope ..
Very frustrating i think its time to update .
i will of cause try and fix the old ones but at the moment i can't do much when i have this intermittent problem and have a scope to work with who knows could switch it no now and it will work again .... :roll:
The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Harry Dalek
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