Restorer's dream part 2 the chassis.

[Danny]

Hi re caps on these ekco,s I havent read all this thread but be on the lookout for what i call bumble bees in the if thay cause instability and must be replaced to keep you sane . i missed one once on one of these and the agc went haywire. when i found the one i had missed it was hiding behind a resistor but when i went near it with my meter the picture improved.Ive never forgot this.Danny

[Heatercathodeshort]

Hello Colin,
Have a look at post 161. This explains where the vision detector diode hides away. Remove the wire clip from the side of the I.F. transformer and slide the top off. You will find it mounted on the top soldered to two tags. It can be checked with a meter but if you have an OA90/91, best to replace it as it is often faulty. The patterning and unstability is probably due to a few O/C decoupling capacitors connected to pin 8 of the 30F5 vision and sound I.F. amplifiers. [Danny mentiones] The stages tend to 'take off,' oscillating causing havoc with the sound and picture. When I get home tonight I will illustate their positions and how to set the tuner biscuit local oscillator correctly. I will also double check the diode connections. Sounds a lot of work but easy, honest. If your good wife does any knitting, that will help..Explanation later. Regards, John.

[Sideband]

Originally Posted by Retired

The vision detector diode? I'm game for anything so please point me in the right direction as I'm not quitting until the job is done.

Post 161 where HCS has shown the diode hidden inside a can. You can probably replace it with an OA91.

Really excellent work so far. The picture still looks a bit negative to me and changing the vision detector may help although it could be that the interferance limiter is set too high.

The vision interferance limiter is usually a pre-set control somewhere on the set and it was adjusted to help reduce the effect of interferance (usually caused by electric motors) that would cause white 'sparklies' to appear on the screen. The idea was to set the limiter until the sparklies were just turning grey which was less noticeable. However if it was advanced too far, the effect would be to 'clip' the whites in the picture, turning them grey, possibly even dark grey so in some cases you can get a 'negative' effect on the picture.

Just a little more information to get your teeth into!

The problem with restoration of old TV's is that people who are just getting into it are not familiar with the operation of the controls simply because nearly all of the controls have been engineered out of TV design over the years. It's only old codgers like us who used to be in the trade and actually repaired these sets who remember the likes of an interferance limiter and a spot-wobble control.

Sorry...crossed with HCS!!

SB

[Sideband]

Originally Posted by Retired

Its so easy to miss things as a novice and the simplest bit of information or advice can usually be interpreted a number of ways leading to silly mistakes. Take for example the sound advice to "CHANGE ALL PAPER CAPS". This to me meant all the waxy caps but the one that caused me the problem was metal cased and to be honest I had my hands full trying to absorb the masses of information already kindly afforded me without researching what kind of cap this one was.

They are better than waxies but will deteriorate over time.

Originally Posted by Retired

I've restored many vintage radios and always found my Hunts Component Tester to be a very good instrument for testing caps; if the cap tested OK then it would work on the radio but now I find I can no longer fully trust this instrument when it comes to TV work as it would appear a TV is very sensitive to the condition of it's caps. Upon the first test the cap in question passed test on the Hunts perfectly so was re-fitted much to my grief. But now I understand just how important caps are on TV work in future it will be a case of replace with new;

Radio's are more forgiving but I would never refit an old waxy audio coupling capacitor even if it measured OK. Try heating a 'good' old waxy (or metal clad) capacitor up whilst testing it. The results could be quite educational! The problem with component testers is that they cannot simulate actual working conditions which include heating and cooling so the results are only an indication of condition at the time of testing. Engineers motto: If in doubt check by substitution!

Originally Posted by Retired

I must say that I've always even tested new caps before fitting.

Probably not necessary if you know them to be new stock (rather than NOS). I do it sometimes to compare with the original being replaced.


SB

[Heatercathodeshort]

Hello again Colin,
I have taken the chassis out of my Ekco T331 with VHF radio.
The I.F. plate is almost identical with yours so a few pictures may help. First just check that you have the frame clipper diode connected the correct way round. Second,slip the can off the vision detector and check the diode or if in doubt replace it. I can send you one if you don't have one. Next to check is the I.F. decoupling capacitors from pin 8 of the 30F5 valves. There are four in all, two sound and [V8 and V9] one common to both sound and vision [V3] and the most likely and the first to check is the vision I.F. amplifier V4, all pin 8. There is H.T. at these points so take care when testing. A good .001uf [ .001uf to .003uf can be used for test] can be bridged across while the receiver is operating but you have to be careful not to short to chassis! Keep the leads short if testing live. If the capacitors are of the ceramic type they are generally good and can be passed over for the time being. If they are the type that look like resistors they will need to be replaced and that will no doubt clear up your instability. Just concentrate on the ones connected to pin 8 of the valves for now. Finally you may have wondered what that plastic bung was in the side of the cabinet? It is to gain access to the oscillator coil to whichever channel 'biscuit' is selected by the turret switch. The usual procedure was to select a THIN plastic knitting needle with it's end sharpened to resemble a screwdriver blade. The bung was removed, the fine tuner set mid way and the needle inserted through the side of the tuner with great care to locate the brass core in the tuning oscillator biscuit. This was then turned either way a very small amount untill the tuning was correct, usually maximum sound consistent with good picture definition without a buzz on sound [vision on sound] or lines varying in sympathy with the picture [sound on vision]. My mums needles were raided on a regular basis and it was difficult to explain to her that metal ones were not suitable. Any thin non metal tool can be used for adjustment but apply only the minimum of pressure as the coil former can be damaged. They are a lot tougher on the Ekco than most. Most important! Do not adjust any of the other slugs through the remaining holes. This should take you a bit closer to success with maybe just the AGC to sort out and possibly the sound. Leave the sound till last. The order of things. Check clipper diode, vision detector diode, decoupling capacitors and finally tuning. Check you have the channel 1 coils in the correct position. I presume your Aurora is tuned to channel 1? It's very easy to slip them back incorrectly so the numbers don't line up with the channel selector! Bye for now, John.

[dominicbeesley]

I think Col said he'd used a 1N4007 as a replacement for the frame clipper diode....will that work or will it be too slow. Maybe better off with something else?

Dom

[Heatercathodeshort]

Hello Dom,
Should be OK. The sync is solid as a rock on Ekco receivers and I have used almost any diode to hand with success. Colins looks a bit unstable and maybe off tune destroying the sync pulses. Once we have got that out of the way it should be easier to see exactly what faults remain. Sounds difficult and complex with the state of that receiver but the chassis itself looks better than a couple of mine and they work very well! Hold the banner high and march forward. [I'll beat the tambourine..]Cheers, John.

[dominicbeesley]

Ha, ha, nice one john, I have to admit to still not quite understanding how these frame-interlace diode thingys work...however on the TV I'm "making" at the moment the frame diode which is a random one I found on the floor seems to work...line sync is just coupled by throwing a wire over the top of the line-osc circuit!

Dom

[Heatercathodeshort]

I built an early pattern generator that picked it's line sync up in an identical way. To put it in a simple way it allows only frame sync pulses to pass. The line pulses are filtered out with an R/C network a bit a sound interference limiter circuit. J.

[Retired]

Hi,

First I must say sorry to you John for asking a question that you have already answered in great detail regarding the "vision detector diode" I really must try to keep up.

You've gone to a great deal of time and trouble John in order to take the pictures which are of immense use to me; thank you. I've had a mixed day today as I could only get into the workshop at 2 o'clock this afternoon but I was very keen to get cracking having printed all the information and pictures off that John kindly supplied.

I noticed your first post this morning before setting off and in my ignorance spent a bit of time surfing the web for an OA90/91 valve; yes go on have a good laugh as I'm not scared of admitting my mistakes. I actually had this on the list to check yesterday but became side tracked with the lathe then lost the plot a bit.

I've now located the diode and I certainly don't have a replacement John; I don't like taking advantage of your generosity John as you have already gone well out of your way to help and I'll pop over to Maplin in Barnsley in the morning to buy a couple of these diodes; many thanks for your kind offer to supply one; I've just checked and they stock OA90 Signal Diodes at 49p each; is there anything else I might need whilst there?

I took your advice and checked pin #8 of each 30F5 valve and having already been caught out twice with caps didn't take any prisoners; I changed them installing new 0.001 635V items. I could only find three of these valves though and assume an equivalent has been installed. At this point I thought enough is enough I'm fed up of trying to find my way around this chassis without a proper valve layout so I broke off and drew my own taking every valve out to add its identity to the drawing so the picture below shows the valves fitted to my chassis; I did this also to try to put a bit back in the hope that it will help others working on one of these popular sets.

Another little setback is that I've only just found the circuit diagram covering Vision IF stages as I was initially puzzled whilst looking for valves 3 & 4; I hadn't realized I had yet another diagram to play with but once again I'm now on the right track.

The three caps I've replaced have made quite a difference; the picture is now much more stable and has stopped rolling so some good progress has been made. The picture shows the removed caps plus the removed can.

Regarding the "frame clipper diode" I'm pretty sure its replacement is installed correctly but to be certain I've included a picture of the original with a pair of new ones showing the way I fitted the new one.

Thanks for enlightening me regarding the plastic bung on the cabinet side John; when I replaced the cabinet side I didn't drill for the bung as I hadn't a clue what it was for. I hope I can set the chassis up on the bench and I'll find a length of thin plastic rod to do the job with. Bron doesn't knit but would you believe I'm an experienced knitter? I used to work 12 hour night shifts knitting Crimplene and Jersey; I'm also an experienced weaver as I used to weave over a mile of blanket in a shift on a fibre loom.

Thanks SB for all the information; yes I found the Vision Interference limiter which is a knob on the back of the chassis and have just read how to correctly adjust it.

Once I get into the workshop tomorrow I'll go through all the information again that I've printed off today. Its nice to see improvement after each session and another thing I noticed is that the two vertical bands to each side of centre on the test card are becoming more distinct. I don't think the parade is far away John.

Kind regards, Col.

[Heatercathodeshort]

Everything looks good by your pictures Colin. Probably time to check that tuning core after you have replaced the OA90/91. You will need a very thin plastic rod as it has to enter the small former that the oscillator coil is wound on. The core is brass and the former plastic so only a small pressure is necessary. Locate the slot in the core and give it a small turn either way observing the changes. You may discover it tunes in very well. I have a hunch it will...You may need a couple of .01uf and maybe a .02uf for the sound audio stages but you probably have these. Cheers, John.

[Mike Phelan]

Hi Col

Just disappeared for a day and you've nearly finished it! You've probably got a diode now but if not, I've a good selection of Ge ones.

[Retired]

Hi,

Thanks John. This really is exciting stuff as I'm so near now to getting this chassis fully working and I'm confident you are right about a bit of twiddling of the tuning core will make a lot of difference.

I got out of bed this morning planning to have a trip out to buy the diode; I had decided against visiting Maplin as they seldom have things I require in stock so I intended to visit Farnell's in Leeds. When I checked my emails my chum David had contacted me as he is visiting on Thursday and is kindly bringing me ten diodes and also when I logged onto the forum my chum Mike also has some this on top of the very kind offer from John; I'm sure it must be Christmas. Thanks everyone for your generosity. I know I'm a tight Yorkshireman but honestly I let the moths out occasionally.

Kind regards, Col.

[Station X]

I had decided against visiting Maplin as they seldom have things I require in stock

You can always check stock levels at your local store online before visiting.

[HamishBoxer]

Think we used to use a size 11 Plastic knitting needle for trimming oscilators cores.

David

[Retired]

Hi,

Thanks Sean for the good tip to check the local Maplin store stock online. It must be over two years ago that I visited three Maplin stores; Barnsley, Sheffield; (Hillsborough) and Stoke on Trent each time taking a wish list with me. At each store the staff were very obliging but I got fed up of being informed that the items I needed but not in stock could be collected the day after if I ordered them.

The next time I visit Carole's Crafts in Batley with Bron I'll buy a pair of size 11 knitting needles; Thanks for letting me know the size David; as other novices will be reading this it's worth pointing out that the needles need to be the plastic type just in case steel needles are still available.

I popped over to see Mike this morning and Mike kindly gave me a pair of diodes and a suitable length of thin plastic rod. I've now fitted the diode and can adjust the biscuit having filed the rod to a screwdriver tip using a needle file.

I've spent ages playing with the adjustments on this chassis and can see improvement; the test card is becoming sharper but now I find I can't fully centre the picture from side to side as there is an unwanted band down one side as can be seen in the picture. In the two stacks of vertical blocks each side of centre a number of the blocks are now displaying individual line patterns which is very encouraging. I feel I need to yet change a few more caps and perhaps resistors to get the picture just right but what a transformation. The dark band across the bottom of the screen is caused by the camera so please ignore; it is the vertical band to the right I'm unable to delete.

I've noticed another small black Hunts cap and a number of small fat 220p but then the chassis is bristling with many small caps; each one I replace is one less to cause trouble.

We have some very welcome visitors tomorrow and Thursday but I'll keep popping into the workshop at every opportunity.

Kind regards, Col.

[HamishBoxer]

You are so near now.

David

[Heatercathodeshort]

Looks VERY good to me Colin. Have another look at post 144. If you unlock the locking screw you can move the shift lever from side to side to raise the picture and pull it up/push it down to move it horizontally. Only a very slight adjustment is required, rather like a bomb aimer! Lock it again after setting. I reckon you are 85% completed. Just the low contrast [diode maybe] and the sound. Simples. John.

[ppppenguin]

Looking much better. I can't see a band down one side of the picture. There's a bit too much width. Correct width is when the castellations to the left and right of the test card are both visible and the points of the little triangular bits halfway down just touch the edges of the screen.

Plenty of sets in people's house were a lot further out of adjustment than this!

[ThePillenwerfer]

That's looking very good, Col.

I was going to stick you a knitting needle in the post so thanks for reporting that you're sorted on that front.

- Joe