BRC 3000 Line Timebase Module: Rare First Gen

My 25 inch 3000  (Rediffusion RT514/25) has this early LTB panel fitted.

Hi Malc,

I forgot about your early Rediffusion 3K that's another then, I wonder if there are any more out there.

This morning I spent some time cutting and shaping the missing piece of PCB. Its slowly getting there, it may not be a perfect colour match but once glued filled at least it will be a lot neater. Once the missing components are installed it should be a little less obvious.

The photo below shows the new piece offered up and held in place with blutack. The mark pen on the edge is the file line to match the break, I'm still working on it.

Nice job Chris, you will soon have it working, Malc.

OK its not going to win a beauty pageant but looks aren't everything.

The missing piece has been shaped the best I can do, its held in with two wire stitches and the join filled with milliput and epoxy resin. This will be put to one side now for a few days to let it all cure. The next task will be two lay down the missing tracks and repopulate the missing components. A little satin varnish will tone down the colour mismatch.

The whole board will then get a thorough clean with the PCB cleaner I got from Malc's Speedy Spares, it works wonders and should have this looking half decent. Then onto the wiring and missing beam limiter.

Impressive work there, almost a grave-yard case but.....  Chris'll fix it ! 

Update

The new rebuilt PCB corner has set reasonably well, slight flexing showed it has a good mechanical bond to the rest of the board. The edge pin stitching should help with keeping it all in place. I decided to carefully drill out the PCB mounting post hole and while I'm at it lay down the missing tracks.

The tracks are a tricky & fiddly job but got there in the end, having other LTB modules helps with seeing how to replicate the missing layouts. These will need to thoroughly dry before they are drilled for the missing components and circuit posts.

New tracks tinned & continuity tested, all passed.

Component holes drilled.

LOPT post J was missing (takes fly lead from point C of LOPT), new one sourced and hole drilled and fly lead fitted from LOPT.

At this stage I'm not wasting new components prior to testing.

W506, BA148 fitted (fitted from scapper, tested ok)
C526, 50uF (fitted from scapper, tested ok)
C527 270pF (fitted from scapper, tested ok)

Next Steps......

clean PCB

Solder in all existing loose components/dry joints.

Fit missing interconnect fly leads

Fit new Beam limiter and attach all fly-leads.

Test on Jig, voltage checks and oscillator waveforms.

Basket cases usually turn out to be less trouble.....bet it works first time!

I wasn't going to press on with this module at the rate I have but I sort of got engrossed and I'm quite eager to see what results I get.

This morning the module was put through PCB cleaner and then rinsed under the tap. This was followed by a long drying session with a hairdryer and then buffed up with brushes. It came up rather well.

I then went over the entire rear panel addressing loose components and suspect dry joints. The wires that provide connections to the beam limiter had been chopped off quite short so they were extended. I then sourced a replacement beam board soldered up and then fitted and locked down with three new screws.

Last preparatory work will be to fit the missing fly-leads and then test.

PCB and output transistors looking very clean now.

Found some spare interconnect leads, one set joins the LTB to the PSU, the other is to the convergence panel. For testing purposes I only really needed the PSU one but thought I might as well add the other.

That completes the rebuild and preparatory work, next step is to power up and check my rails. If they are present, then see if the oscillator is running and if I have the 8kV pulse at the EHT nipple.

More to follow........

Chris said

That completes the rebuild and preparatory work, next step is to power up and check my rails.

http://nuclearsecrecy.com/nukemap/?&kt=0.02&lat=54.6640414&lng=-1.6779571&airburst=0&hob_ft=0&fallout=1&zm=15

Nice one 

Cathovisor said

Chris said

That completes the rebuild and preparatory work, next step is to power up and check my rails.

http://nuclearsecrecy.com/nukemap/?&kt=0.02&lat=54.6640414&lng=-1.6779571&airburst=0&hob_ft=0&fallout=1&zm=15

  

Nice one Catho

We're ready in Yorkshire too

Marc. 

I know there is a distinct absence of thermionics in my threads and I'm sorry to also report there was also a lack of thermonuclear detonation.

Just to be sure the PSU this LTB would be connected to had zero faults, I powered it up on the jig first without the LTB connected. To simulate a line pulse in this scenario to get the 58-65V rail to present itself, you hook the line pulse wire from the test unit to the -ve end of W608. When powered up all rails were present an correct, good, the PSU works and is happy on the jig.

Next I hooked up the early MK1 line timebase module to the PSU, removing the simulated pulse from W608 then powered up.The rails came up but stopped at the 30V one, the 58-65V rail fails to establish. Therefore its fairly safe to say the line pulse must be missing. 

likely suspects are :-

1. C511 25uF short-circuit
2. VT501, VT502 faulty
3. C512 .015uF short-circuit
4. Broken connections on L501
5. W507

Further investigation required.

W507 was short-circuit.

Replaced and now the oscillator is running......the 8kV pulse is present, nice purple spark can be drawn from the EHT nipple.ITS ALIVE!!!!!!!!  < simulate lightening strike >