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BRC 3000 Line Timebase Module: Rare First Gen

 
crustytv
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The BRC 3000 was launched in 1969 and the first generation sets had a line time-base module that had a few notable differences to the module that followed a year later. This was the use of two line output transistors VT504 & VT505 both R2009's the later module used a single R2008. The driver transformer T502, is a huge affair compared to the later modules which was much smaller and finally the fly-back tuning was a pair of .056uF 400V caps in series instead of the later singular .028uF 800V. There are some other subtle component differences but I don't intend to go into them now.

I don't know about other collectors but I've found this module to be extremely rare. I have six 3K sets and 4 spare line time-bases, until recently I had never seen one, all mine and the ones I've seen in other collections have the later time-base.

Last year I was contacted via the main site asking if I wanted a couple of old BRC modules, I gladly accepted and through the post I received a PSU and a time-base module. To my delight the time-base module was the 1st generation as described above.

Its battered, bruised and its been through the wars. Many components and wires are hanging off, there is also some significant damage to one corner. This being a missing piece and along with it a few components, including the interconnecting tracks that completed the circuit. As this to me is such a rare module I plan is to completely overhaul it, repair the damage as best I can replacing the missing PCB section and using my track repair kit rebuild what is missing from the corner.

I had a really battered and broken I/F panel and will use a section of that to rebuild the corner. I will remove any traces that are present and have marked out the exact break to match the missing piece. I will use my Shapercraft scrolling machine to get a precise cut then epoxy them together. Then using a plan view rebuild the tracks, drill the component holes and repopulate.

The beam limiter sub panel is also missing but I have a spare so that's not a problem. Once all the loose components have been rechecked and resoldered, the missing plugs etc, then the real fun of power up and testing will begin. This will be a side project to my TV repairs, I don't anticipate dedicating my sole attention to this. That way I will not get bogged down and can enjoy other projects as it slowly progresses.

Just thought I would post and share my thoughts about it and perhaps some others here may already have a set running with a first gen LTB installed, if you do it would be good to hear your experiences with it.

ltb-1.jpgltb-2.jpgltb-3.jpgltb-4.jpgltb-6.jpgltb-5.jpg

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Topic starter Posted : 02/10/2016 11:39 pm
malcscott
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My 25 inch 3000  (Rediffusion RT514/25) has this early LTB panel fitted.

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Posted : 03/10/2016 9:38 am
crustytv
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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.

ltb-7.jpg

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Topic starter Posted : 03/10/2016 4:35 pm
malcscott
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Nice job Chris, you will soon have it working, Malc.

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Posted : 03/10/2016 5:27 pm
crustytv
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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.

ltb-8.jpg

ltb-10.jpg

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Topic starter Posted : 03/10/2016 6:16 pm
PYE625
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Impressive work there, almost a grave-yard case but.....  Chris'll fix it !  thumb_gif

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Posted : 03/10/2016 9:55 pm
crustytv
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Posts: 11259

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.

tracks.jpg

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Topic starter Posted : 04/10/2016 2:48 pm
crustytv
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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)

ltb-a.jpgltb-b.jpgltb-c.jpg

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.

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Topic starter Posted : 04/10/2016 10:31 pm
sideband
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Basket cases usually turn out to be less trouble.....bet it works first time!

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Posted : 05/10/2016 1:51 pm
crustytv
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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.

ltb-d.jpgltb-h.jpgltb-f.jpg

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Topic starter Posted : 05/10/2016 2:00 pm
crustytv
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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........

ltb-1c.jpgltb-1b.jpgltb-1a.jpg

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Topic starter Posted : 05/10/2016 2:57 pm
Cathovisor
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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

grin_gif

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Posted : 05/10/2016 3:11 pm
Marc
 Marc
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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

grin_gif  

Nice one Cathorolf_gif

We're ready in Yorkshire too bang_gif

Marc. 

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Posted : 05/10/2016 4:14 pm
crustytv
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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.

ltb-pwr1.jpg

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Topic starter Posted : 05/10/2016 5:39 pm
crustytv
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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 >

ltb-work1.jpg

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Topic starter Posted : 05/10/2016 9:19 pm