It is currently Wed Dec 13, 2017 12:09 pm

Dynatron CTV28

 
Posts: 49
Joined: Tue Nov 26, 2013 8:05 pm

Dynatron CTV28

Post by davyrocket2 » Thu Aug 25, 2016 3:42 pm

well I have just won the auction £20.00 the seller states its model is a ,CTV,28 .Is it a 26,inch version ? and I noticed it does work and on the front controls the brightness is up ,no 6 ,but the contrast and colour settings are not very high the picture does not look fab but I am sure that other members are aware it is not easy to take a good picture ,as it can be influenced by room lighting and if the camera use"s a flash so I hopeful this is the case and not a low emission tube regards David
Last edited by crustytv on Wed Aug 31, 2016 7:47 pm, edited 4 times in total.
Reason: relevant posts from the suppliers section thread now merged into this new repair thread

 
Posts: 5844
Joined: Sat Jul 23, 2011 8:19 pm

Re: Dynatron CTV28

Post by crustytv » Thu Aug 25, 2016 4:14 pm

davyrocket2 wrote:well I have just won the auction £20.00 the seller states its model is a ,CTV,28 .Is it a 26,inch version ?

Well done David, you've not only bagged yourself a bargain but also a nice early CTV too. The Dynatron CTV28 is dated as a 1974 set, it is indeed a 26" CRT and the chassis it used was the PYE 733 series.

Personally I would pay no heed to the control settings as any indication of the CRT condition. People especially non techy's just love to twiddle knobs. As you say best to wait and see when you've got it and given it a service.

 
Posts: 298
Joined: Thu Jul 19, 2012 3:07 pm

Re: Dynatron CTV28

Post by slidertogrid » Thu Aug 25, 2016 8:44 pm

I would change the capacitor on the A1 supply. If it shorts it can take out the tripler, LOPT and line output transistor and that can be a swine to change! It might pay to change the flyback tuning capacitor at the same time..
:thumb
Rich.

 
Posts: 49
Joined: Tue Nov 26, 2013 8:05 pm

Re: Dynatron CTV28

Post by davyrocket2 » Sun Aug 28, 2016 4:28 pm

I collected this set yesterday the cabinet is in very good condition ,However its not working firstly a badly fitted 3 core mains lead has been fitted and not very well with sellotape to stop it shorting out ,2nd item the 800ma ,fuse under the mains dropper has failed but it does not show any blackening maybe it failed from age I am wondering does anyone know of causes of failure for this there are cobwebs and dust but no signs of nicotine stains which leads me to think it was owned by a non smoking family I am taking pics of the inside and will try to upload them later I will consult my computer guide /windows ,vista ultimate , lastly the tube fitted is ,A66/410 ,is this a delta gun type,?,am I correct in thinking , in line tubes started about 1977 ish ,memories are thorn 9000 ,and phillips ,G11 come to mind ,regards David

 
Posts: 5844
Joined: Sat Jul 23, 2011 8:19 pm

Re: Dynatron CTV28

Post by crustytv » Sun Aug 28, 2016 4:45 pm

davyrocket2 wrote:The tube fitted is ,A66/410 ,is this a delta gun type,?

I don't know about a A66 410 but the A66 410X is a quick heat Cathode, delta gun, 110 degree tube.

 
Posts: 1141
Joined: Mon Jul 25, 2011 11:37 am
Location: Willington, Co Durham.

Re: Dynatron CTV28

Post by malcscott » Sun Aug 28, 2016 6:11 pm

The A66-410X is a quick heat version of the A66-140X, Malc.

 
Posts: 49
Joined: Tue Nov 26, 2013 8:05 pm

Re: Dynatron CTV28

Post by davyrocket2 » Tue Aug 30, 2016 2:32 pm

well the first test revealed the resistor above the mains dropper is short circuit all I have manged to find out that its rated at 30watts ,am I correct that its a special ? it seems to be in a heatsink so does any ideas for a suitable replacement ,and I require information regarding the chopper transistor and the lopt transistor and as mentioned earlier the values of the 2 capacitors that can cause lopt/tripler failure and lastly location of the A1 adjustment pot and also can someone explain how can I get servicing info and is this in the libary and what do I have to do to download this I tried to google the model and chassis info pye 733 on google and think that it was covered in television magazine many years ago by les lawry johns

 
Posts: 5844
Joined: Sat Jul 23, 2011 8:19 pm

Re: Dynatron CTV28

Post by crustytv » Tue Aug 30, 2016 5:06 pm

I think you're confused and I didn't help, let me address that and make it very clear for you.

The chassis in your Dynatron CTV28 uses the PYE "733" chassis. The "733" chassis is based on the "731" but, it has many variations and additional circuitry, hence why it gets the "733" identity.

What's in the "733" and not the "731"?

It gets a little more tricky, the "733" has ultrasonic remote although your CTV28 does not have this option. Then there's electronic touch tuning, VCR compatibility, headphone and and tape cassette outlets. Many additional I.C's. Also apart from main H.T. all H.T/L.T rails and the tube heaters are scan-derived.

There are further subtle board variations on the "733" too with caveats that some boards cannot be used from the "731" and also many board revisions which are identified by a code printed on them. For example the tube base panel, depending on the CRT fitted because of the quick heat cathode options. As you've already stated you have the 410X CRT the you do have the quick heat cathodes and therefore the modified CRT PCB. Power supply panels there are a couple of variations to that so theses too are not interchangeable.

So on the whole you're looking for "731" data but with the additional need for the "733" circuitry additions/modifications.

The 731 and 733 data is not in the library.

I do have the official PYE manufacturers "731" service manual and all the version mods (725,735,737,741) and of course the "733" but they are HUGE ( many pages) and due to recent events, I have no inclination to spend the vast time it would take to scan them all.

However if you start a repair thread ( or I can split this one off ) in the appropriate section, I will be more than happy to provide relevant circuit snippets in the form of high res photos to assist you as you progress through the sets repair.

 
Posts: 1141
Joined: Mon Jul 25, 2011 11:37 am
Location: Willington, Co Durham.

Re: Dynatron CTV28

Post by malcscott » Tue Aug 30, 2016 6:17 pm

The metal clad resistor is 3.3 ohm if i remember. No seperate A1 control, individual ones for each gun. No chopper transistor, psu is thyristor, BT116/SCR957. BU208A line output transistor. I would replace all the h/v caps in the line cct, and the mains filter cap on psu, Malc.

 
Posts: 49
Joined: Tue Nov 26, 2013 8:05 pm

Dynatron CTV28

Post by davyrocket2 » Wed Aug 31, 2016 6:22 pm

I managed to replace the resistor above the mains dropper and after attending to many dry joints the set came to life but I then noticed the main dropper was glowing a bright orange colour I manged to hear hissing through the loudspeaker but fearing more damage could be caused I turned it off I suspect there is a very heavy short somewhere but not having a circuit diagram for it I am unsure where to look next no line whistle or tube heaters or signs of any ht any advise welcome regards David

 
Posts: 5844
Joined: Sat Jul 23, 2011 8:19 pm

Re: Dynatron CTV28

Post by crustytv » Wed Aug 31, 2016 6:56 pm

davyrocket2 wrote:I suspect there is a very heavy short somewhere but not having a circuit diagram for it I am unsure where to look next

Regards David

As a one-off ( I don't normally load full circuit data into the forum) and a gesture of good will, here is the circuit for the 731.

Perhaps as a start disconnect all the other boards from the rails leaving just the PSU module. If the short condition goes you know the fault lies elsewhere, then its just a case of hooking one up module at a time to find which module. If however the fault stays when all boards are disconnected, you've isolated it to the PSU module.

Power Supply Description
psutxt1.jpg

psutxt2.jpg


The PSU module, layout and voltages
731PSU.jpg
For the visual reference benefit of others, the 731 PSU module

psulayout.jpg
The 731 PSU layout and voltages


High Res: Entire Circuit Diagram for 731
It was a very large sheet so I had to carve it into 4 separate scans, they should join up though. They are high res PNG.

731-3.png

731-4.png

731-5.png

731-6.png

 
Posts: 489
Joined: Tue Mar 24, 2015 12:01 am
Location: Wigan

Re: Dynatron CTV28

Post by nuvistor » Wed Aug 31, 2016 7:18 pm

Oh dear, going on 40 years ago I repaired these and that circuit and PSU photo do not bring any memories back at all. How much we forget. :bbd
Frank

 
Posts: 298
Joined: Thu Jul 19, 2012 3:07 pm

Re: Dynatron CTV28

Post by slidertogrid » Thu Sep 01, 2016 3:13 pm

I would expect the HT fuse to blow before the dropper glowed red hot? Has someone replaced the fuse with something more than 1A?
Check the BU208A on the line panel. The fixing screws are usually soldered in so getting the transistor out can be a pain.
However the Transistor usually fails by going totally short all junctions so you may be able to just unsolder the emitter and base connections to do a check.
If the transistor is short it's then a case of what damaged it. suspects are the A1 capacitor, LOPT and tripler.
It is sometimes possible to see the melted turns on the LOPT if you look at the bobbin closely.
Good luck!
Rich.

 
Posts: 2853
Joined: Wed Jul 27, 2011 7:13 pm
Location: Croydon

Re: Dynatron CTV28

Post by sideband » Fri Sep 02, 2016 1:06 pm

It could be one of the large smoothing caps. C880 if the 3.3R is very hot or/and C877 if the the 56R and the 3.3R are getting hot. They are before the 1A fuse.

Personally I'd cold check the electrolytics first and then the silicon.

Mind you, I'd expect the 3.15A fuse in the mains to blow unless someone had stuck a nail in there......!

 
Posts: 49
Joined: Tue Nov 26, 2013 8:05 pm

Re: Dynatron CTV28

Post by davyrocket2 » Wed Sep 07, 2016 2:35 am

after careful removal of the LOPT it is short circuit so is the BU208A and I am sure the tripler is at fault I have not yet removed the A1 cap pr the 2 smoothing caps but feel both should be replaced as a pair any ideas please of source of replacement items ? if anyone has these items costs of course including postage will be met and I would think a decent tube is as rare as rocking horse poo

 
Posts: 5844
Joined: Sat Jul 23, 2011 8:19 pm

Re: Dynatron CTV28

Post by crustytv » Wed Sep 07, 2016 11:59 am

davyrocket2 wrote:after careful removal of the LOPT it is short circuit

Can you elaborate, how did you test that? Have you tried ringing the LOPT on the scope.

davyrocket2 wrote: BU208A .......... any ideas please of source of replacement items ?

Plenty of BU208A available on e-bay http://www.ebay.co.uk/sch/i.html?_from= ... 5573.m1684

davyrocket2 wrote:I am sure the tripler is at fault ..........................any ideas please of source of replacement items ?

If the tripler is toast and potted with silicon, it can be repaired. If its potted in hard epoxy, game over for it.

davyrocket2 wrote: anyone has these items costs of course including postage will be met and I would think a decent tube is as rare as rocking horse poo

Why a new CRT, have you tested it ? If so what were the emission results, did you try a clean and balance . If you've not tested it how do you know the emissions are low to warrant replacement.

 
Posts: 1141
Joined: Mon Jul 25, 2011 11:37 am
Location: Willington, Co Durham.

Re: Dynatron CTV28

Post by malcscott » Wed Sep 07, 2016 12:19 pm

Loads of nos BU208A here, should have triplers in stock as well, Malc.

 
Posts: 49
Joined: Tue Nov 26, 2013 8:05 pm

Re: Dynatron CTV28

Post by davyrocket2 » Fri Sep 09, 2016 12:08 am

I have a mate whom is a qualified tv,engineer who trained and used to work for radio rentals he used to do mainly audio and vcr repairs he was here last sunday and bought a scope with him the lopt was ring tested I have just got some BU208A and a,BD183 from ebay the tube was tested and all 3 guns in the red we tried to gently clean it but it did not respond I was also given a envelope with the set showing its purchase 2nd hand in 1985 and some receipts for work carried out ,1992 a regunned tube supplied by well view tubes and tripler replacement so I hope maybe a universal tripler and lopt,regards the tube is there any way that I can use a transformer to help the tube heaters

 
Posts: 298
Joined: Thu Jul 19, 2012 3:07 pm

Re: Dynatron CTV28

Post by slidertogrid » Fri Sep 09, 2016 9:07 am

In my experience 110 degree delta gun tubes don't respond well to reactivation they either die completely or go flat again within a short time. I don't know If the cathode coating was thinner?
There are various ways of increasing the voltage to the heater you could use a separate suitable transformer but a easier way is to try lowering the value of the series resistor in the heater supply. I don't know if this chassis is the same heater circuit as the 725. That set had two resistors on parallel on the tube base panel. ISTR they were 2.2 or 2.7 ohms.
I suggest getting the set working first and seeing what the picture is like, often tubes that read poor can give surprisingly good pictures. They also often improve after a few hours running. When I first got a picture on my Decca 30 the tube looked a bit poor but after a long run it came back almost perfect and has stayed that way. Once you give it a blatt on a booster the clock is ticking.
Rich.

 
Posts: 5844
Joined: Sat Jul 23, 2011 8:19 pm

Re: Dynatron CTV28

Post by crustytv » Fri Sep 09, 2016 9:20 am

slidertogrid wrote:I don't know if this chassis is the same heater circuit as the 725. That set had two resistors on parallel on the tube base panel. ISTR they were 2.2 or 2.7 ohms.

Out of interest I take it that would be R833 & R834 ( 82K) as shown in CRT cct post #11 ? Bit confusing as R864 & R865 (1.2R) are paralleled as you describe, but a I can't see how you go about lowering them much more so don't think its them :qq1

 
Posts: 1141
Joined: Mon Jul 25, 2011 11:37 am
Location: Willington, Co Durham.

Re: Dynatron CTV28

Post by malcscott » Fri Sep 09, 2016 10:23 am

Could the loptx be re-wound? :aaq

 
Posts: 433
Joined: Tue Apr 16, 2013 4:43 pm
Location: Coventry, but originally from Holland

Re: Dynatron CTV28

Post by ntscuser » Fri Sep 09, 2016 4:57 pm

slidertogrid wrote:In my experience 110 degree delta gun tubes don't respond well to reactivation they either die completely or go flat again within a short time. I don't know If the cathode coating was thinner?
There are various ways of increasing the voltage to the heater you could use a separate suitable transformer but a easier way is to try lowering the value of the series resistor in the heater supply.


Won't that shorten the life of the tube even further?


Return to Colour Television



Who is online

Users browsing this forum: No registered users and 2 guests