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Old 16th Sep 2011, 9:05 am   #161
Heatercathodeshort
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Default Re: Restorers dream part 2 the chassis.

One item I failed to mention Colin was the location of the vision detector diode. It lives in solitary confinement under a cover secured by a spring clip, on top of the final vision I.F. transformer. As you can see I replaced the one in mine many years ago. They often deteriorate over the years going either high resistance or leaky giving a washed out picture. An OA90/91 serves well. J.
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Old 16th Sep 2011, 9:41 am   #162
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Default Re: Restorers dream part 2 the chassis.

As so many guys are following your thread Colin I thought it might be worthwhile to post some pictures of the Ekco tuner and the position of the .1uf AGC decoupler as the tuner was employed, with very few changes, in a huge range of Ekco receivers over a ten year period. The tuner coil 'biscuits' are easily unclipped [spring retainers] but are not so easy to refit as they are a bit tight. Make a note of the positions before removal. They are usually marked with channel numbers so it will also let you know what channel coils are fitted in your particular receiver. Ekco usually were quite generous here. My new replacement cap can be seen in the last picture. J.
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Old 16th Sep 2011, 10:14 am   #163
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Default Re: Restorers dream part 2 the chassis.

Hi,

After such a long exciting day yesterday I slept like a baby last night and this morning I think I'm back on the planet.

Thanks Greg; yes it was a very easy mistake to make with the Metrosil but one I'll never forget.

Thanks for the Aurora information Geoff; every bit helps and such useful tips can save a great deal of time and frustration.

Yes Lee I really did fall for it and got caught out but not being used to this kind of work I wrongly assumed the EHT reached the CRT at the coils on the CRT neck and this was why I felt I needed to exercise care whilst touching items such as the ion trap magnet. only when I slowed down and really thought about the problem did it occur to me to have a look at the circuit diagram as I suspected EHT wasn't reaching the CRT at all and Mike's suggestion of putting my hand very near the screen to see if the hairs stood up was a brilliant bit of advice and just so easy to check; it was this simple tip that gave me the clue and once I looked at the circuit diagram I knew instantly that I had solved the problem. It just shows how easy it is to trip up whilst following very simple instructs (remove the Metrosil; it will work without it) my interpretation of this must be a classic but hang around I'm sure to cause more laughs before this restoration is fully completed.

Thanks Howard; much appreciated.

Have a great trip Dom and your vintage Land Rover and Myford lathe will be waiting for you to return; please drop me an email when you get back.

Thanks for the advice Jeffrey and the Aurora model number is; SCRF-405A Rev 2.0/2.1; I'll also find channel 1; the channel knob is broken and at the moment I've fitted a radio knob in order to turn the selector. Dom very kindly sent me the Aurora details ages ago so I'll have to find them as they are filed on CD.

Many thanks John for your continued help and advice; I'll copy and print this off; I'm pleased you pointed out that the caps and resistors look alike so have taken note; colour codes on these items are totally wasted on me and I have to resort to identifying against the circuit diagram or I'm forever asking Bron to help out; Bron is this blue love; no its purple!! Bron is this brown love; no its green!! It is highly frustrating for me but I have to live with it and work around it; imagine me working in a nuclear power plant.

Thanks for the advice on connecting the Aurora up but Mike has let me know he is bringing some coax with him so I can do a posh job. Whilst Mike is here he can also point out the resistors and caps you mention John; this will save me tripping up again (hopefully).

Out of interest I was wondering what I could do once this restoration is finally completed and already I have the next project lined up which should prove interesting; I have two rather expensive Aumann electric coil winders but only one foot control and this foot control has packed up also one of the counter displays is faulty; I'm never bored.

Kind regards, Col.
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Old 16th Sep 2011, 10:50 am   #164
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Default Re: Restorers dream part 2 the chassis.

Colin

I think that once this restoration is complete you should take a little time off and enjoy viewing the TV before you start anything else.

Looking forward to seeing pictures soon.

Keith
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Old 16th Sep 2011, 11:39 am   #165
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Default Re: Restorers dream part 2 the chassis.

Cross dressing capacitors caused me a lot of 'fun' during my Eddystone 770R rebuild. I first assumed they were innocent resistors, but when I had problems with low IF gain I realised they were capacitors and nearly all leaky or open circuit. I'm not a fan of shotgun replacement, but in this case I had to.

However one big difference between restoring radios and TVs in the modern age is that a TV won't be used on air so doesn't need every dB of gain.

Because the Aurora has such a large output (6mV) it's a bit like living down the hill from Ally Pally! You can get a very good picture even if the RF/IF sections in your receiver aren't at their best. Hopefully the picture on the screen will tell you where to go next.

Keep an eye on any wax paper decoupling caps on the heater chain as if any of these suddenly decide to go short they could really spoil your day by taking out / stressing a load of filaments.

Good luck!

Paul
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Old 16th Sep 2011, 1:44 pm   #166
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Default Re: Restorers dream part 2 the chassis.

Good advice from Paul.
I too have had heater decouplers go short and now I always make sure that they are replaced.
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Old 16th Sep 2011, 5:47 pm   #167
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Default Re: Restorers dream part 2 the chassis.

Hi,

Thanks Keith but I don't have time to stand and stare although I will run the TV occasionally; it will be a good talking point for visitors.

Thanks for the excellent advice and good wishes Paul; I've changed all the wax caps with the exception of about two and these will also be changed very shortly.

WOW John; thanks so much for all the information and picures; I noticed it after I added my last post. I've already printed it off and taken it into the workshop where it will prove immensely useful.

What a most interesting afternoon I've just had watching a professional at work. It was a pleasure to have Mike Phelan in the workshop and the rate Mike was working I was sure Bron would be watching Corrie on the set tonight!!

It's many years since Mike worked on one of these but I wouldn't have guessed as he got stuck in and it didn't take long before the test card appeared briefly having hooked up the Aurora. As luck would have it the PY32 expired with a nice bright glow but although I would have had to wait for a new valve Mike casually added a short to get the heater chain up and running then soldered a temporary rectifier diode in and was back in business in no time.

As Mike worked I kept asking questions and when I popped out to make a drink Mike pulled the channel selector drum out and yes John the 0.1uF cap was in dire need of changing so Mike soldered a 630V item in but left me to re-fit the drum after firstly explaining in a lot of detail how I should go about it. Your advice came at a perfect time John because I could ask Mike to point out the caps which look like resistors etc so I've got a better understanding of what I need to do in my next session.

Mike made everything look incredibly simple and made a great deal of progress in such a short visit; I'm very impressed indeed.

One thing I was not impressed with was Poundland new 9V batteries; I had a pack of two which died within minutes of use with the Aurora; I'll spend a bit of time and hook the Aurora up to the lab PSU then won't be worried about powering it up in future whilst I work. I hope I'm not being unkind to these batteries as I don't know the power consumption of the Aurora.

I still have plenty more work to do and it will no doubt take me some time but to see the test card flash up briefly was the icing on the cake; the picture of the test card was badly distorted but it was there and I can't thank Mike enough; what a tremendous difference it makes to have someone so skilled by my side; it took me back many years to my apprentice days and I enjoyed myself.

As Keith rightly says I need to take a rest so will relax a bit tonight and spend a bit of quality time with Bron who has never complained whilst I've put the hours in on this set; I'm positive she deserves some retail therapy next week so will take her over to Boundary Mills in Colne which is our favourite retail outlet.

Kind regards, Col.
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Old 16th Sep 2011, 6:11 pm   #168
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Default Re: Restorers dream part 2 the chassis.

Well done. You've seen pictures.

An Aurora takes about 250mA which is very unkind to a PP3.
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Old 16th Sep 2011, 6:33 pm   #169
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Default Re: Restorers dream part 2 the chassis.

Jeffrey is spot on, try to find a power supply, i use a 500ma keyboard psu with mine, it works a treat
Looking forward to seeing a good rendition of testcard c!

Mark
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Old 17th Sep 2011, 9:21 am   #170
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Default Re: Restorers dream part 2 the chassis.

Thanks, Col.
I actually quite enjoyed it, not having repaired a valve TV for half a century or so.

For completeness' sake and for others to see my approach, I'll just fill in what I did.
On firing up the set, there were a few sparks from the PY32 - not good, but we soon had a raster and both line and frame hold controls worked, as did brightness.

It was possible to select a channel from the Aurora and fine tune the set to get some "noise" on the screen, then the heaters went out; PY32 had finally died!
Bridging the heater pins and sticking the 1N4007 in brought the set back to life and briefly we managed to tune the makings of a test card before it just went back to a tunable mush.

The screen and anode voltages on the vision IF stages and video amp looked OK, as did putting the meter lead on the grids of the IF stages - the screen display changed, so it was a fair assumption that the fault was in the tuner, probably either one of the valves or the notorious 0.1 mfd decoupler.

The valves were quite hot so I guessed they had emission.

A quick test was to remove the bottom and side covers so the fixed contacts could be accessed; the front one is for the mixer, and had HT on two of them (mixer and local osc anodes). The back one is for the cascode RF stage, and only had a few volts on the 30L1 anode connection, so 0.1 was s/c.

As the fixed contacts would be tarnished we decided to take the drum out; the top screw attaching the tuner has to be removed so the tuner can be swung up to disconnect the spindle from the TV/FM cam. The 0.1 thought it was a 4k resistor, so out it came.

I really wanted to see a test card, and I don't like leaving jobs incomplete, but had to get back home then, so will be watching the thread with bated breath!
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Old 17th Sep 2011, 4:30 pm   #171
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Default Re: Restorers dream part 2 the chassis.

Hi,

Thanks Jeffrey Iím glad I didnít blame the Poundland batteries too much; the 250mA drain explains their quick demise.

Thanks also Mark; please see the following.

Thank you Mike for adding your technical explanation of what you did yesterday; there is a huge gap between our knowledge of TV work; Yes it was a pity you had to leave because we enjoy your company and it wasnít a problem at all that you could not finish off as it left me something to do and a bit more to learn. You moved me on light years and I was delighted when the test card did flash up so knew the set wasnít far off working.

I donít know why I bother going to bed sometimes as I was wide awake again in the middle of last night this time thinking about my life in general. When I made my first enquiry about TV and received lots of replies a caring friend thought I was being dragged into TV work against my will as to be honest I had absolutely no interest in TV other than I had seen a really rough looking TV cabinet in The Bulletin.

What have you all done to me? During this chassis restoration I felt as though I was living in virtual reality but last night I came to the conclusion Iím in fantasy land. It took four months work to restore the cabinet and I had a clue about how to do that but this chassis is different. Itís only about a fortnight ago that I had never tried to work on a TV chassis but here I am confidently re-installing a channel selector drum having not removed it myself; Iíve drawn 1Ē long EHT lightning from a U25 and lived to tell the tale and Iím slowly finding my way around the chassis. In two weeks from wreck to showing a test card; it would have taken me longer but Mike helped a great deal yesterday although I believe had I changed as I planned to do the 0.1uF cap inside the tuning unit as described by John the test card should have appeared? What I did learn from Mike was his approach and it was a pleasure to watch his technique at problem solving; credit to Mike for helping and it was Mike who got the first glimpses of the test card to appear not I.

This is not just a radio forum I think its open university. Really top class experts and very decent guys have helped me considerably on a one to one basis by taking me by the hand and explaining in great detail each stage in such a way that even a novice like me could understand and the results speak for themselves. None of the overbearing health and safety issues just simple instructions on what I should avoid to prevent receiving an electric shock and I was more than happy to get stuck in. Jeffrey not only gave excellent information but kindly donated two U25 valves and now John has also informed me that he is not only donating a PY32 valve but even has a suitable channel knob and is to post both on to me. I feel truly humbled by what has happened to me over the last couple of weeks and offer my most sincere thanks to everyone concerned.

My friend was indeed correct; Iíve been drawn in to TV restoration work and how can I return to radio work now after seeing a picture come to life the way I did; Iím doomed.

I was in the workshop by 8.30 this morning raring to go and spend the day on this chassis. Iím sorry guys but hanging an Aurora on with a bit of old wire is just not my style. First thing I did was to tidy up as the bench looked like a bomb site. I moved everything to its proper place then searched for a reliable 9VDC supply for the Aurora and found a really nice PSU fully variable up to 30V so coupled this up and I also made a neat job of adding proper coaxial cable; I double checked the voltage was indeed 9V before switching on. Yes shame on me for being so tidy and neat.

Now I was happy and settled; next job was to check around before re-fitting the selector drum and I noticed another cap that I thought worth changing whilst the drum was out and it was tucked well out of the way; I couldnít make out what it was so just snipped it out leaving a pair of ľĒ long tails to solder the new cap to. Big mistake: it proved to be a 2uF high voltage cap and I didnít have a new one so had to spend time re-fitting it.

I polished all the drum contacts and the connection fingers using Solvol Autosol then had a go at installing the drum. Mike had told me to watch out for the spring loaded lever at the top of the enclosure and at this point I realized I needed at least three hands; in the end I propped the lever up by simply placing a nut as shown in the picture taking care of that problem. It was still rather a struggle to get the drum home and the retaining spring clips into place but I managed; Mike had also told me which way the drum went in because it is so easy to install it 180 degrees out. I then remembered to remove the nut and re-fitted the covers.

Now for the moment of truth and I switched on; I also switched the Aurora on and waited; at first there was all sorts of rubbish on the screen but after a lot of knob twiddling at last the test card was showing and stationary; it wasnít perfect as the height was and still is way off but the picture show how good it is at this stage and to me it is very good to say the set has been asleep for many years.

Our climate is wonderful; I had a choice of taking the test card pictures through the workshop window either in a downpour of rain or brilliant sunshine; I took a total of fourteen pictures just to get a decent one as shown. Just as I had done this Bron came to me rather upset saying there was an injured pigeon in the back garden. A couple of hours later we were back home after a visit to the vets. On arrival at the vets the pigeon had died during the journey there but at least it died amongst friends and not alone. We were both sad because we like all the wildlife that visits us.

After dinner I changed the remaining two wax caps; one was on the height control but when I checked there is still a problem with the picture height; twiddling all the knobs I can obtain picture height but then everything becomes grossly distorted with a rolling picture of sorts.

Iíve still some way to go but from wreck to a test card in two weeks is beyond my wildest dreams. Please note all other novices contemplating tackling a TV restoration; donít do it; run away before you too are doomed like me.

Kind regards, Col.
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Old 17th Sep 2011, 4:35 pm   #172
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Default Re: Restorers dream part 2 the chassis.

A slight frame linearity issue there I think.....

Excellent results though

Sean
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Old 17th Sep 2011, 4:50 pm   #173
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Default Re: Restorers dream part 2 the chassis.

Hello Col,

I may be way off the mark but, going by the black bar near the top of the raster, which could be the field blanking interval, it looks to me as though the frame timebase might be running at half its normal rate, that is 25 fields per second instead of 50! Perhaps you could try adjusting the field hold control to see if the black bar can be eliminated, thereby showing a single frame, instead of what appears to be two fields one above the other, albeit with the top one extremely compressed vertically?

Regards,

Dave.
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Old 17th Sep 2011, 6:40 pm   #174
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Default Re: Restorers dream part 2 the chassis.

Col, what you now have is a superb diagnostic instrument in the TV itself. The screen can now tell you so much. Even if you don't fully understand what it's saying the pictures you post can speak volumes. In the post before mine Dave has made a suggestion about the field timebase. He may well be right.

Now is the time to complete the re-capping. John's approach of one cap at a time is admirable but a bit too tedious for me. I tend to go section by section, for example do the whole of the field timebase and get it working nicely. This may also involve the odd resistor change too as some, especially those over 100K, may be well out of tolerance.

PS: There's a ghostly apparition holding a camera visible just above the test card
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Old 17th Sep 2011, 7:00 pm   #175
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Default Re: Restorers dream part 2 the chassis.

Hello Jeffrey,

Quote:
Originally Posted by ppppenguin View Post
In the post before mine Dave has made a suggestion about the field timebase. He may well be right.
Thanks for 'sort of' confirming my diagnosis!

Regards,

Dave.
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Old 17th Sep 2011, 7:37 pm   #176
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Default Re: Restorers dream part 2 the chassis.

I've been reading with interest and must say Well Done Colin!!

I hate to disagree with anyone, especially Jeffrey, but I too tend to test after each capacitor and I'm hardly a beginner! You can see the set improve with every capacitor you change and you can see what every capacitor does as well. (Hunts caps it's usually 'falls to bits' but there you go.')

Look also at resistor values here too. They tend to go high. The sawtooth that the frame oscillator should generate should start at the top of the screen and then go down as the voltage increases. It starts near the middle in this case!

Check for dry joints on the tube neck as well.

Cheers,

Steve P.
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Old 17th Sep 2011, 7:44 pm   #177
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Default Re: Restorers dream part 2 the chassis.

Steve and John between them have probably mended more TVs than I've had hot dinners. Doesn't stop me being an impatient so and so who wants to get on with changing too many caps at once. Pobably reflects a difference in background; mine in design, theirs in maintenance. I'll tend to take it back to how the designer intended, often pondering exactly what the designer did intend. This doesn't of course help when the designer's intent was wrong or even perverse, neither of which is not unknown.
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Old 17th Sep 2011, 9:10 pm   #178
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Default Re: Restorers dream part 2 the chassis.

Hi,

Thanks Sean; I need to learn all the terms but I'm getting there.

Thank you Dave; I've played with every knob I can find but it remains the same; I can adjust to obtain one picture but this deletes the test card and just gives a lot of rubbish.I'm interested to learn of the frame timebase perhaps running at 25 instead of 50? Is this Hertz; 50 cycles per second? Would this also have to to with rectification such as half and full wave rectification if so then would a faulty diode throw the time base out; I'm thinking in terms such as the single diode used to bridge the faulty PY32 valve? Sorry if this is a truly dumb question but there is all-sorts whizzing around in my head as I try to understand what is going on. It's highly likely the questions will get dumber as a little learning is a dangerous thing.

That's kind of you Steve thanks for the comments. I've noticed plenty of small Hunt's caps so will end up working through them and I'll see how I go whether to blanket replace a section at a time or replace the lot as I'm confident of not losing the connections using my miniature coil winder. I really do need to find my way around the circuit diagram and then I can work on one section at a time to see what if any difference there is.

I also need to test the audio and believe the Aurora injects an audio signal? There is so much to try to learn at once but it's fun.

Every day progress is made and I feel quite relaxed as the hardest part could well be behind me; I've probably dropped myself in it now by saying that.

Kind regards, Col.
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Old 17th Sep 2011, 9:19 pm   #179
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Default Re: Restorers dream part 2 the chassis.

Hello Colin,
Looks like there are some capacitors there that are leaking so badly they are probably in need of nappies. You need to take care here and concentrate on the ones I marked green on the earlier circuit. I have a PY33 and a channel selector knob packed up and waiting to go on Monday. I chassis tested the PY33 and it works fine. The PY33 has a 29v heater so it might be better to wait until the rectifier arrives before the receiver is run for long periods. It looks great so far. Have you got a Mazda valve data book or similar to give you the valve base connections? If not I can probably find you one. It will be a lot easier if we can identify the valve elctrodes when chatting. At this stage, now you have an actual test card I still think it better to replace one cap at a time. It is so easy to make a mistake when doing a blanket change and I always suggest this to guys that are working on equipment without good layout diagrams. Get the picture right first Colin. The audio is easy. Cheers, John.
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Old 17th Sep 2011, 9:53 pm   #180
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Default Re: Restorers dream part 2 the chassis.

Hello Col,

Quote:
Originally Posted by Retired View Post
Thank you Dave; I've played with every knob I can find but it remains the same;
OK, that's a pity!

Quote:
I can adjust to obtain one picture but this deletes the test card and just gives a lot of rubbish.
It's possible that the frame hold could be set so that the frame 'rolls' very quickly, that could give the effect you describe. Adjusting the frame hold shouldn't delete the picture! It's also possible that you may have been adjusting the line hold, having that set off-frequency could also cause that effect. Once you have the set fully working, you should be able to observe the effect of adjusting the line and frame hold controls to see just what they do!

Quote:
I'm interested to learn of the frame timebase perhaps running at 25 instead of 50? Is this Hertz; 50 cycles per second?
Yes, the frame timebase normally runs at 50Hz (= 50 fields per second). As the line and field frequencies are locked together with a specific relationship to give an interlaced display, you get two fields per frame, the frame rate being 25Hz (= 25 frames per second).

Depending on the range of adjustment of the frame hold (or because a/some components(s) have altered in value) you may be able to adjust it so that the time base runs at 25 Hz, you would then get two fields displayed one above the other, instead of interlaced!

Quote:
Would this also have to to with rectification such as half and full wave rectification if so then would a faulty diode throw the time base out;
No, the field frequency is determined solely by the field timebase, which is synchronised to the the field sync pulses in the video signal. As the mains rectification is half wave anyway, you couldn't get a condition where one diode of full-wave rectification had failed!

Quote:
I'm thinking in terms such as the single diode used to bridge the faulty PY32 valve?
No, the PY32 is a single diode as half-wave rectification of the mains supply is used.

Quote:
Sorry if this is a truly dumb question but there is all-sorts whizzing around in my head as I try to understand what is going on.
There is no such thing as a 'dumb' question! If you are not clear about how something works, you have to ask questions, no matter how 'dumb' the may appear to you!

Regards,

Dave.
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