CTV New addition, Baird M708

@colourmaster 

They did have a good picture, only ever saw one well before Wimbledon 67. Would have been earlier in the year, could have been late 66 not sure now. Winter Hill just had a still photo test transmissions. It was the first CTV the college obtained.

That looks a nice set Gary.

I look forward to its restoration story

I remember the full service data is more than just data. It is a bible, fully comprehensive and inclusive of everything you need to know and more. I found it vital when I repaired an M708 which I owned.

Here is a link to it and I hope you find it of some interest and use....

https://www.radios-tv.co.uk/community/colour-television/baird-m708-dual-standard-colour-television/

It was an epic journey for me I will never forget and of course the superb picture that rewarded me for the effort. Truly a masterpiece of design.

Hi Everyone

I made a start this afternoon on the set ,

I checked for shorts then started it up gently on the variac. At 80% I could hear the timebase start up then as I increased the mains the timebase stopped followed by the boost diode glowed red hot , I quickly switched off and checked the boost cap which had gone short . After replacing the .47 uf boost cap the timebases started up then a blank raster appeared , the brightness controls the raster but it's blank . The sound can be heard with a signal on both 405 and 625 . As I was about to start checking the video board there was an almighty bang and a flash , the mains filter cap blew .  I should have replaced it at the start . Anyway the mains fuse has blown , I can't read the value , could it be 1.5 A .

Any advice would be appreciated .

Regards.

Gary

Hi 

Again I've  just noticed this loose lead hanging from the IF board , it's soldered to a resistor then just loose at the other end . It's attached to resistor R92 . I'm working without a manual at the moment as I can't find mine .

Are you sure it is F1 that has blown? It's worth mentioning that there are two fuses on the TV.

F1 is the main fuse and is 2A. The other fuse, F2, is 250mA, and is there to protect the system switch solenoid circuit. It was a known fault with this TV that if the system switch had not mechanically located or there is an electrical fault in the switching cct, it would blow F2.

Anyway, you at least now know the fuse values. 👍 

Very odd, that wire from R92, looks like a bodge not on either of my Bairds nor shown in the manual. I wonder if someone was attempting to hard-wire to 625, R92 is certainly associated with the system switch tags 22/23/24. Might be related or maybe not.

In situations like these with unknown sets, with potential untold service bodges, I spend days going over the whole TV evaluating what is what before apply any power. That's just me though, anal 😉 appreciate everyone has their own methods.

Hi Chris, thanks for the info . It's the mains fuse behind the main connector that blew because of the shorted mains filter cap . Regarding the stray wire , Ken's son told me that he last used it in 1984 to record some 405 line material .

That could explain the wire , I'll check the system switch contacts in case they've been tampered with .

Looking forward to this one!

Hi Everyone,

Spent a little bit more time this afternoon we are now back to where we were originally yesterday . Good sound but no vision , TR 9 is running very hot so I'll check that tomorrow. Could anyone tell me was function this transistor has ? Video. I've no circuit so need your guidance .

Regards Gary

Hi Chris, so sorry I've just noticed the section of the circuit you sent ..

Many thanks.👍

Hi Gary, all you need to do is refer to my repair blogs for the M702 and M718, the whole component line-ups are listed along with their function

https://www.radios-tv.co.uk/1968-baird-m718/

https://www.radios-tv.co.uk/1968-baird-702/

Hi Chris, 

I certainly will read your restoration posts  , tomorrow I'm going to remove the if panel and check the system switch and that TR 9 .

Regards Gary

Hi Gary, I wasn't suggesting you read all of my blog posts, I'm no example to follow. It was just to suggest if you're unsure of a particular transistor, valve or diodes function, they are all detailed right at the beginning. I'm sure you'll have this TV up and running in no time, compared to my usual bumblings 👍 

Hi Chris, I will enjoy reading your blog on the Baird especially the repair of the mask . I was wondering what to use and thought about fibreglass resin .

Hopefully a picture will appear tomorrow on it's screen .

Regards Gary .

Posted by: @colourmaster

[....] especially the repair of the mask . I was wondering what to use and thought about fibreglass resin .

Hi Gary, initially I too thought about using fibreglass, but that stuff scares me. Mainly because I've no experience to speak of except on one attempt at another repair, that being on a Ferguson 3703. The cabinet had been dropped by the previous owner and the fascia had broken in multiple places. I did manage to get it fixed, but it was tortuous to say the least. It needed to be a strong repair, as the  all the CRT weight is supported from it.

For the Baird mask, due to it not being structural, I decided to go down simple porous, surgical matting and then painted it over with two part epoxy resin. Once cured, even though the rear of the mask was not visible, I colour matched it as best I could. Externally you can hardly notice the cracks I had and what's more it's rock solid.

I hope your LOPT behaves itself more than mine did, and don't be surprised if you have to rebuild the tripler, though its a really easy job.

Hi Chris, thanks for your advice on the mask repair , I have all the broken pieces to glue back in . I'll keep an eye on the lopt and the tripler . 

Regards Gary

Hi Everyone

I thought I would spend the morning on the Baird as Mrs P is away until Tuesday , I replaced the TR 9 as it was reading strange . I now have what looks to be no sync and poor luminance , the video input lead from the IF panel that goes to the video / chroma panel was plugged into the left pin so I studied the photos of Chris's set and the lead should be on the right hand pin . There is another wire that has been added to the bottom coil on the timebase  so I will investigate that . This set seems to have been " modified" in certain areas .

 On the plus side the decoder seems to be working .

When the cats away, the mice will play 😎

Excellent progress Gary 👍  Looking at the manual, the coil the wire is attached to is L405, the width coil. I suspect, like the other rogue wire attached to R92, and what you mentioned above, probably related to the person setting up 405 standard.  You would think, just switch the TV to 405/625, for whatever standard you needed.

Have you established that the standard switching is functional? That it is meshed on a standard? Have you scoped it to see what frequency the timebase is running at? Maybe the SS wasn't working, or maybe it had been hard soldered to 625, hence making the wire jumps for 405 necessary. Perhaps all related to your sync problems. All very strange, though very intriguing.

Hi Chris,

I'm thinking that these faults could be man made , I'm going to take the chassis out completely and have a good look at the system switch . It seems to switch standards ok .