Kolster Brandes RV 10 (Crown)

[sexton_mallard]

Originally Posted by Heatercathodeshort

I would suggest you replace the sync coupling capacitor C55 .1uf between the anode of the video amp to the grid of the sync separator. It will probably be leaky. You will probably have to back check all your work due to the mass change of capacitors. It's very easy to make a mistake that can be very frustrating when fault finding. J.

Thanks John. This cap was already replaced with a correct value. I checked and rectified 2 more mistakes with replacement caps in the volume/brightness control area with C77 missed out and C97 connected incorrectly. This set rewarded me with another complaint... The source of the rustling noise on the audio revealed itself when after reseating all the valves, a burnup started on the valve base of V6! It looks like the cotton sleeve protecting the coil/resistor choke L43/R59 from the pentode anode of the PCF80 has started to short with an adjacent valve pin! Carefully cleaning the mess away and moving the pins sorted it! The components appear to be unharmed and what a relief as this looks to be a heater-cathode short in the CRT which was not the case.

The situation with the picture is largely unchanged. A faint ghosted distorted test card is visible on channel 6 not channel 1 as expected. Channel 1 has sound but no picture apart from horizontal white lines. (I did ensure the tuner coil disc went back in the same position when it was cleaned). A double check of all components and their placement seem to show no issues although on my set the contrast and noise limiter controls seem to be the other way round than what is shown on the documentation. Hmm. The horizontal and vertical hold seem to be fine with the picture locking so we have problems 'up the line'. I am working from the aerial socket towards the tuner checking components. I did think of thinking of feeding a composite video signal (decoupled via caps) into the video amp from the Aurora video output. But for now more homework on the theory of monochrome TV operation and troubleshooting.

[Heatercathodeshort]

These chassis are very straightforward and reliable. The faults you are encountering and the screen display still suggest you have got something wrong that may be man made.

I would suggest you break the circuit down into sections, IF, sync separator, video amp frame timebase and print it off. Check each component in turn and when you are completely satisfied that section of the circuit and the component values fitted are correctly wired, mark the checked component with a highlighter on you circuit. This is the only way to sort out a chassis that may have incorrectly wired components. It's frustrating I know but it is a lesson learned. One component at a time testing after each replacement. It takes a bit of experience to veer from this path and even after years of servicing it is still possible to muck it up! Good luck with it. John.

[sexton_mallard]

This has made my year so far!! I changed the Aurora to channel 2 and slowly the test card appeared over 10 to 15 minutes. I had to back the noise limiter back otherwise the picture balloons out and goes dark. I think I have a PL81 in there that I cremated during my fight with the EHT problem. After end to end checking I found no problems. I have to leave the set on for 15 20 minutes so possibly tired valves waking up and electrolytics reforming. Watch this space....

[sexton_mallard]

I treated it to some video for probably the first time in decades. The picture does not disappoint. I grabbed the Roku/NowTV dongle out of the lounge and plugged it into the HDMI2AVI converter. The yoke is just bodged in at the moment with no magnets. I'm not sure if it even needs the linearity sleeve yet as the yoke kindly supplied by John seems to be fine. Sound is a bit distorted so I will check around the audio stage later. That picture was taken in the shed near bright daylight, that CRT is amazing. Chuffed.

[Heatercathodeshort]

That looks a fair picture and a good CRT. Just as a guide, the frame linearity should be 100% when sorted but don't expect a good interlace performance.

KB had a bad scan coil design that is even more noticeable with the pre dual standard 110 degree models. Modified scan coils were supplied but rarely requested due to the average viewer being quite happy with the non interlaced picture. Your almost there! An increase in picture size with increased brightness is usually due to a low emission EHT rectifier. It is probably a R20 equivalent to the Mazda U26. It might be an R19 with a 1.25v heater. They are not interchangeable. John.

[sexton_mallard]

The set has been running for a few hours each evening and after a few minutes of some twitching of the screen (which I assume is one or more valve holders with a poor connection warming up), the picture is nice and stable. I tidied up around the line stage capacitors and swapped the deflection coil connections around and routed the wires back in their little conduit to get the picture the right way up.

Sound is distorted still and I have replaced the grid coupling cap on the pentode of the audio PCL82 as a precaution and can hear no difference. I will substitute the valve and listen. The picture needs more height and to be pulled over to the right. I will experiment with the two small bar magnets and linearity sleeve to see what happens. The height pot is right over to one end so I was thinking of a lower value coupling resistor (which was already replaced) on the control if I can't get the height right. I suspect the replacement deflection coils will be a bit different from the originals.

[Heatercathodeshort]

Check the value of R84 10M in the sound interference limiter circuit. It may have risen in value. Make sure you have replaced C74 .01uf and C78 .03uf. The bar magnets will not shift the picture over. There will be either a picture shift device fitted just behind the scan coils or adjuster rings actually mounted on the scan coils.J.

[sexton_mallard]

Originally Posted by Heatercathodeshort

Check the value of R84 10M in the sound interference limiter circuit. It may have risen in value. Make sure you have replaced C74 .01uf and C78 .03uf. The bar magnets will not shift the picture over. There will be either a picture shift device fitted just behind the scan coils or adjuster rings actually mounted on the scan coils.J.

Thanks John. Both C74 and C78 have been replaced (the latter with a .047uf cap which was the nearest value). R84 was up to 12.5M but I have left it in for now as clipping one end out of circuit for testing and bridging with a new 10M resistor made no difference.

I have made a bit of a different discovery however. When I first connected the aurora set to channel 1, the picture on channel 1 on the set was a scrambled mess. What I did not realise at the time is the test tone on the test card c is triggering a sound on vision fault totally obliterating the picture. I switched the aurora to channel 2, and 3 channels on the set give pictures of varying quality. The one I was using as shown on the earlier pictures was a bit smeary bit it did have sound - but - distorted. The reason is I had the sound almost turned up to maximum as the sound was tuned out maybe not to trigger the sound on vision fault. I have a channel which give a cracking picture when no sound is playing or the video is paused but as soon as the sound starts the picture breaks up to the sound. Turning the fine tune knob showed me the effect of going in and out of tune with the sound clear and undistorted by with a scrambled picture but a good sharp picture with the sound off or video paused. Getting closer!

I have tried attenuating the signal from the aurora in case the signal was overloading the front end but this make no difference. I have also picked a test channel and adjusted the tuning slug (3 clicks anticlockwise with a trimmer tool) and can get a really brilliant picture as long as there is no sound!

[sexton_mallard]

The time this set is taking is getting to the stage where it may not be finished before the next Ice Age starts...

I have been running the set for 30 minutes or so each weekend on the bench in the shed to keep the the damp out of the set. Sound is disconnected as not to trigger the sound on vision fault for now. The other day I noticed the picture getting dimmer. A check of HT showed a voltage down to 195v from about 230v dc with a current of 170mA so it looks like the selenium rectifier is calling time. I don't think the HT is getting pulled down by a fault from the current reading but then again I may be wrong. A 750ma fuse in the circuit suggests the current draw is acceptable here.

A silicon diode and a wirewound power resistor in series with the original rectifier out of circuit restores a nice bright picture with no ballooning with the brightness turned up. Now to go through the IF to troubleshoot the sound on vision. Some of the IF cores look a bit damaged as if Mr. P Twiddler has made a visit but for now I will leave well alone.

[sexton_mallard]

HT is now 230-235v but the dimming of the picture is still happening...after about 30 minutes of use, the picture after switch on from cold nice and bright at first. A check of boost voltage shows a drop to about 430v. Suspecting the dreaded damp LOPT saturation syndrome is happening, the patient has been prescribed rest with a warming DC current flowing through the LOPT for the next week or so. the PL PY and U26 rectifier valves were all NOS replacements and the screen resistor R68 looked a bit overheated (probably from my first attempts in trying to get something on the screen), the resistor was replaced again.

[paulsherwin]

Thread reopened by request.

[sexton_mallard]

Back to it! The fading HT has been resolved and no more fading occurs after extended running following a drying out of the LOPT overwind and storage over winter indoors next to the airing cupboard. The silicon diode and resistor has been retained for now for the mains supply.

My motivation is buoyed up at the first picture seen below. This is with no magnets and the scan coils still loosely resting on the CRT neck. I have long suspected that some twiddling has gone on.

I managed to get channel 1 to correspond with that from the standards converter from tuning the channel coil in the tuner which was near Channel 2 before and the sound peaks in the middle of the fine tuning but the picture 'whites out' from the test tone from Test card C in the Aurora. Attenuators are used...in fact I had two piggybacked in the aerial lead! The tuner AGC seems to vary from -3 to -4v but goes positive up to +1 volts when the interference occurs. The interference limiter makes no difference implying the fault is 'upstream'.

Playing actual video shows the sound on vision as well. I checked all components in the IF section and as I am receiving a good picture and sound where I expect it to be, I think the sound and video IF alignment can't be miles out. The sound is clear and un-distorted.

Substitution of the tuner valves and the 6BW7 vision IF valve made no difference.

I focussed on the sound trap circuit and checked everything including the 2 caps in the can with a component tester. All seems fine. I then connected two test leads across the coil in L26 and with my multimeter connected there is an improvement! The meter changing or providing some kind of tuning change perhaps. This is temptingly leading me to tweak the sound trap L36 coil but I am resisting here.

Does what I describe seem to make sense that the sound trap is misaligned and is not filtering out the sound from the signal passing into the video IF stage?