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1977 Aphelion TV :Telefunken 712 Chassis

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crustytv
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Thought it might help to visualise where everything is for those like me, who are new to the Telefunken 712 Chassis, layout and modules detailed below.

Found and replaced one of those notorious WIMA's (C401) in Power supply module I, which was blown. Tested the main smoother (C403) which is looking good. Next onto Power supply module II

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Posted : 21/07/2016 3:55 pm
sideband
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Now....did that capacitor fail under load or did the casing just split while it was stored due to moisture ingress? These things like the Refa types seem to split and disintegrate even when not used. Normally if it fails under load, there would be soot and smoke damage and probably some melted plastic. Not that it matters...it's duff anyway! Just idle thoughts.

 
Posted : 21/07/2016 7:30 pm
crustytv
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Onto Power Supply II, the Thyristor regulator module. An in circuit test revealed C427 10uF @ 100V was o/c. Removed and confirmed. I've fitted a 10uF 400V. Also The large can C441 2200uF @ 40V read as leaky everything else checks out OK. Perhaps these 3 cap failures in the power supply modules are the reason the set was retired.

Sods law dictates I have every voltage of a 2200uF below 40V but not 40V :bbd Will order some up and continue this once fitted.

Edit: checked C441 on the bridge at rated voltage yep its totally o/c.

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Posted : 21/07/2016 9:42 pm
Cathovisor
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The large cylindrical thyristor also featured on the 711 chassis. Another quirky feature of the 711 was what Telefunken called "active smoothing" - it was merely an R/C network of large R and smallish C that supplied base drive to a Darlington pair, so the low current provided a smooth voltage to the base as there was next to no ripple, which was then reflected at the emitter of the output stage. AFAICR it didn't actually regulate - it just smoothed.

Very Telefunken!

 
Posted : 22/07/2016 12:01 am
Red_to_Black
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I see the purple electrolytics are performing as expected then. :bba

That German capacitor or a very similar type was used extensively in Grundig sets of the day, and rather than going leaky or low ESR, they could fail either completely O/C or completely S/C, most odd!

Another type of cap that did similar to the German types mentioned above was the Philips light metallic blue electrolytics which ( I think) you mentioned earlier, again most failures in various Philips kit I came across the caps were again either completely open, or short circuit.
I don't know if Rich (Sideband) came across this a lot ? or if his experiences while he was at Philips were similar to mine ?

:thumb for the ESR meter btw.

 
Posted : 22/07/2016 12:11 am
crustytv
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I see the purple electrolytics are performing as expected then. :bba

To be fair to them only one failure out of four on the regulator board, the other three tested fine and were left in place. Still I won't count my chickens just yet, there are 10's of others scattered throughout the other boards so the batting average may go down :qq1

:thumb for the ESR meter btw.

Its the danglies, Peak kit is worth every penny, I certainly should have got one long ago, it certainly speeds up testing in circuit.

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Posted : 22/07/2016 2:01 am
crustytv
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Inspected, tested and cleaned the deflection modules today, Sync,E-W correction, Vertical Osc and Vertical output. The only cap to fail as leaky was C492 2200uF 35V on the Vertical output module.

If anyone is keeping tally on the purple perils, on this suite of modules six purples tested with one failure. Total tested thus far including the PSU modules, 10 with 2 failures. There's still a load more on the I/F, sound, RGB and line timebase.

Next up for testing : Line timebase

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Posted : 22/07/2016 6:04 pm
sideband
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:thumb for the ESR meter btw.

Agreed on the ESR meter!

Once you've used one, you wonder how you managed without it. The one I built a few years ago continues to pay for itself in time saved. I'm using it at work at the moment. In this last week, two PC's have died in the heat (both on Monday after a power outage over the weekend). Another is decidedly sick and difficult to get going. Two have been fitted with new power supplies and the third is running with a borrowed supply from another machine. Rather than throw out the old supplies, I set to with the ESR meter and a bagful of electrolytics. I've recovered two of them by replacing no less than five caps in each (two were obvious and bulging). I need a 2.2uF at 450V to complete the other one. Without the ESR meter it would have taken ages. As it was, a quick run over with the ESR meter found the five dud caps in less than five minutes.

Well worth buying or building one!

 
Posted : 22/07/2016 6:26 pm
Red_to_Black
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Actually Chris's ESR meter is the posher/newer + plus version of the Peak one I bought about ten or more years ago, the Plus version looks to have several worthwhile improvements over my original version.

Mine is the original 60 version, on the newer models one worthwhile improvement is the auto test feature, on mine you have to press the test button each time you want to test, also mine does not show leakage on the display.

still it was godsend even back then :cca

Back to the Telefunken ahem! :qq1

 
Posted : 22/07/2016 6:53 pm
crustytv
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Unlike the rest of the set the Line timebase panel is fixed to the right hand frame. From the vertical position its frame can be swung to latch at 45 degrees or 90, thereby affording good access.

I'm beginning to really like the thought that has gone into the design of this chassis. Telefunken went even as far as to include expected waveform diagrams at the test points on the print side, in the form of additional screen print.

Anyway back to the status, C584 1000uF 50V was the only electrolytic found to be faulty, it was leaky and replaced.

Hoping the 2200uF 40V caps arrive tomorrow as I can then repair PSU module II and finally apply some power to see what we are presented with. Plenty of scope for failure as I've not done testing with regards to other caps, resistors, diodes or transistors. I'm getting the impression from the condition of the panels, components and the CRT emission, this set might not have seen a great deal of hours put on it. Then again it could just have been well serviced and looked after.

Next up for testing: Sound, I/F and RGB

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Posted : 22/07/2016 9:50 pm
Cathovisor
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Now you can see why I'd like a 711 again. That didn't have waveforms on the screen print though!

 
Posted : 22/07/2016 10:19 pm
crustytv
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Removed the RGB module from the signals board, tested the three electrolytics, all passed.

Upon inspection under the bench scope a dry joint was found on one leg of C345 in the blue drive. Hard to see in the photo but when waggled, the leg moves in the pad. Other than that all appears OK.

Its difficult to get across just how well thought out this chassis is, the modular approach is taken to a new level with virtually every element of the set broken down like a circuit block diagram but represented as daughter boards. You can remove every element, RGB, Sound, I/F, Chroma I and Chroma II. Simple interconnect edge pins, a few locating screws and out they all pop. Makes testing and isolating a complete breeze. Then over to the two PSU modules which again are simply removed via a couple of screws and interconnects. The Deflection board is the same story, with the sync, e/w correction, vert osc and vertical output. finally the line timebase is the singular largest module.

No forgetting that the modules can be mounted in the reverse side of the signals ground plane board which eases the ability to do in-circuit testing on the chosen board. This is a great idea and one I have encountered before on the thorn 9000 series chassis but not to the degree available on this set, all very impressive.

That concludes today's work.

Tomorrow: Sound, I/F and Chroma

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Posted : 23/07/2016 12:20 am
Katie Bush
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That's one hell of a professional set up you have there now, Chris - beats my SLR camera lens and pocket torch! :aad

 
Posted : 23/07/2016 12:35 am
crustytv
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Final checks this morning:

Removed the sound, I/F and Tuner modules, all electrolytics check out OK

Checked Chroma I and Chroma II modules, again all OK.

All edge connectors cleaned

Replacement caps for the power supply regulator board arrived and a new C441 has been installed.

Later this afternoon there will be the reassembly, followed by thorough checks on connectivity, then the power on.

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Posted : 23/07/2016 2:21 pm
Cathovisor
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Can't wait for the first application of power :)

 
Posted : 23/07/2016 2:26 pm
PYE625
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Can't wait for the first application of power :)

Nor me :qq1

To understand the black art of electronics is to understand witchcraft. Andrew.

 
Posted : 23/07/2016 6:53 pm
crustytv
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I maybe sticking my neck out here but I would not be at all surprised if the cap failures on the powersupply module 1 and regulator board, were the cause of the sets retirement.

All modules were re-installed and the wiring harness reconnected to all the various points. I decided to throw caution to the wind and not disconnect the tripler. The rational behind this was the sheer excellent condition of all the components, tracks LOPT etc foolish? Perhaps!

So it was time for the big power on ttt: what would we get?

A very red but full raster........ I know from the B&K results that all three guns have excellent emission so its looking like a grey scale is going to be required but there might be something else going on.

Next I hooked up the Test Card generator and then tuned in to test card F. Well the decoders working but the colours are not great due to the dominance of Red. I Need to do some checks maybe its been twiddled or perhaps some voltages/waveforms are astray, we shall see.

There we have it, Telefunken-tastic. Next up will be a read up on how to grey-scale and start checking voltages, waveforms against the specifications and take it from there.

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Posted : 23/07/2016 8:04 pm
Cathovisor
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:aad

Well, next thing - colour to zero, see what it looks like. From the pictures it just looks like the red background control's high?

 
Posted : 23/07/2016 8:11 pm
Marc
 Marc
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Looking darn good Chris :aad

Marc.

Marc
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RSGB call sign 2E0VTN

 
Posted : 23/07/2016 8:15 pm
crustytv
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Setting the TV into service mode which puts the set into frame collapse, I adjusted the three guns. Green and Blue were not set correctly with Red, once adjusted a white line was now visible. With colour off I trimmed RGB drive for Blue and Green, Grey-scale can be seen to be fairly good on B&W now.

Then feeding in colour bar all is revealed with regards to the lack of good colour definition, there is a decoder fault. The red tinge to the card was masking the fact that the ref osc not locked correctly.

Either the reference oscillator needs adjusting ( likely) or it could be the 4.433MHz crystal is on its way out. Going to be tricky now as I don't think the Trader has adjustment data for the decoder. I may just try cheating and replacing the crystal first, might be a quick win.

I can't see where the pre-set is for the ref osc is located. I think I will have to move Chroma I module into the service position on the rear of the signals ground plane,. This will at least afford me open access to the board and I can scope this part of the circuit.

Decoder fun-tastic :bba

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Posted : 23/07/2016 10:51 pm
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