Sony STR-6800 receiver - stiff tuning, dial lamps and...

[stevehertz]

I noticed that the same bulb is used to back illuminate the two small meters, and it is a working bulb. Now, there's more room where this bulb and holder goes, so maybe I can nick it to use on the right hand side of the dial glass, then find another solution - an LED bulb? - to fit into the meter box position. Out of interest, the paxolin bulb holder was broken in two and scorched, so I've superglued it back together - see photo - and I'll also put some strengthening strips on the other side once dry. Oh yes, I'm used to these small jobs turning into epics!

[stevehertz]

The Farnel LED festoon bulbs are all too long at 37mm, I need 28mm. I've found these on the internet, the first ones look very promising if they'll fit as they can be rotated:

http://www.ebay.co.uk/itm/2x-28mm-LE...MAAOSwYGFU10nP

http://www.ebay.co.uk/itm/Pair-12V-2...kAAOSwKIpV-8GE

[Radio Wrangler]

Looks good!

David

[sp10mk11]

I am interested to see if these LEDs are any different in the way they spread light to the ones I tried, all they did was light up the middle ends of the meters.
So good luck and I wait for the next instalment on this
Gary

Ps those pictures bring it all back now

[stevehertz]

I've ordered two of the straight sided LED festoons, so we'll see how they perform. I can always use one of the original bulbs in the meters light box as it is not so intolerant of heat build up there.

BTW, regarding the drive cord problem that I mentioned in the first post, I have since removed the old drive cord and what I though was a stiff tuning cap actually isn't, it was all due to the slack old cord that traction was not being achieved. So, here I go on another first - surprising in a 40 year history of vintage restoration! - a drive cord replacement. 'Shut' your ears while I do it and I'll keep you informed.

[stevehertz]

I've now replaced the ailing drive cord. Wasn't as difficult as I thought it would be, but I did have the Sony instructions for such and they worked a treat - see photo. I used an old tiny wooden reel of RS drive cord that was thicker than what I took off, but frankly I think it's better, it's stronger and it grips the tuning knob drive better. I also took the opportunity to perfectly align the tuning pointer wrt the tuned station, it was about 0.2Mhz out before.

That broken meters lamp mounting board has also now been strengthened with narrow fibre glass strips Araldited in place, as the fix that I had done so far (superglued the two halves back together) would not have stood up to the necessary handling in order to refit it and gather up all the associated wiring back into a loom. Gotta wait for the LED festoons to arrive now..

[sp10mk11]

You are a doing a splendid job Steve I am really pleased to see this come along as I do have a penchant for this range of Sony gear.
I have often used a bit of talcum powder on the rotating parts of the drive system this helps some times. Also the spring tension affects the tension on the cord as you know some times I find slacking this off a tad can give a smoother tuning, providing the tuning can gears etc are all free and smooth
Gary

[stevehertz]

Yep, the spring was hardly tensioned before, and although I made sure that the new drive cord loop was exactly the size specified by Sony in the service data, it is much tighter (stretched) now, and it can only get weaker as they say. So if the cord does stretch, there's room for take-up. I used tiny drops of silicon lube applied with a piece of wire to the centres of the nylon pulley wheels. Tuning is both smooth and free now.

[sp10mk11]

Music to my ears Steve, I love restoring this type of equipment
Gary

[stevehertz]

Interesting view Gary. I've generally always preferred working on 30s and 40s/50s radios and TVs because they are so predictable and generally easy to work on, faults are very often 'visible' to the trained eye and/or electro-mechanical in nature. Modern stuff - that I have kinda had to work on at times I've always found more difficult because the faults are not so obvious, and it's often extremely difficult to get at components to even check them, let alone change them.

In the early noughties I went through a period of collecting, repairing and restoring video machines of different formats, and as you can imagine, they were an absolute pain to work on sometimes, especially the mechanical setups where a few microns can make the difference between a good picture and no picture! But again, a good grounding. So, to this Sony receiver, and I'm really enjoying it. Probably because it's mainly electro-mechanical stuff! If any ICs were dodgy, I'd probably be looking for the fault until I die!

As a writer by trade I also like writing about my restorations, so that goes hand in hand with the forum, and I get great advice from people too.

[stevehertz]

The LED festoon bulbs have arrived and so far, they appear to work a treat. You can see in the photo that they are nice and bright (the photo is taken with flash). I've removed the glass dial to clean it and also to apply fresh green translucent green paint to the ends that had come away as described earlier. So that will be the true test, to see if they are strong enough to 'work with' the filters when the dial glass is re-fitted - I'm pretty sure they will be. Bear in mind that the LED bulbs are fairly directional, so you are looking at the side of them in the photo. When viewed from the front they are eye scorchingly bright albeit with a shimmer, but I don't think that that will be a problem when all the black baffles are in place and they're pointing at the green glass filters etc. So, next job, paint the green dial ends and put it all back together.

[stevehertz]

Now with dial and baffles refitted and green translucent paint applied to dial ends as a filter. The paint is Vitrail Emerald transparent. I'm more than happy with the results, I was expecting some kind of compromise in terms of colour or brightness, but not so. The photo was taken without flash,hence the shake. I'll take a shot of the receiver with the front panel refitted in due course.

[stevehertz]

Here's another photo now that the daylight has gone and with the front panel temporarily in place for the purpose of the photo. The colour is more green than it appears in the photo, although I've noticed that I can 'tweak' the intensity and hue by altering the angle of the LED lamp towards the edge of the dial glass. You can see that the left hand side is slightly brighter, that's because the lamp is angled for maximum brightness or effect on to the edge of the dial glass. The lamp on the right is not so 'focussed' and is actually aesthetically better. So I'll just 'de-angle' the left hand one a tad to level things up. More photo in due course.

[Radio Wrangler]

I found that one of the benefits was simply knowing that I wouldn't have to keep replacing bulbs

David

[stevehertz]

This morning I set out with intent to cure the perceived volume imbalance problem. When switched to mono (as well as stereo) there was a definite bias towards the LH speaker. The balance pot is open backed and I thought that probably the back cover was missing for some reason as a result of a previous attempt to cure the problem. Looking around on the internet, it appears that this is normal - a guy is selling a S/H one that looks exactly the same as mine, it is open backed for one of the tracks. Understandably I thought the track on the open back would have attracted dust and - if anything - had been the problem one, as balance adjustments were still crackly. I blasted it again with Servisol. No better. So although it was very difficult to get at - I had to use the Servisol inverted which meant it would only 'fire' for a split second - I managed to get a few blasts into the front half of the pot with the cover. And that cured the problem; no more crackling, and no more imbalance, the balance pot sits nicely in the middle position now.

So I just have to finally tweak the LED lamps for best position wrt brightness and colour match at each end of the dial glass, clean a few more parts and put it back together. I'll post some final photos in due course.

[sp10mk11]

All this is very good steve. I must admit in the last picture the tuning window looks almost Pioneer display blue, but it does appear evenly illuminated.
Can I ask what you used in the meters as they look very well illuminated in terms of eveness and colour.

Well done for persevering on the controls I remember them as being a sod to get to with switch cleaner spout

I still have an ST-3950 tuner sitting around some where, it is from this range and uses the same display/bulbs etc, so imight drag that out and start experimenting with LEDs and paint again.

Gary

[stevehertz]

Gary, The meters are coloured by their lamp's light passing through a green plastic translucent shrouding that surrounds them. In truth, the green of this plastic is 'less green' than the paint that I have used on the ends of the glass dial (!), so I suspect that it is something to do with the colour hue of the LEDs that is adding the bluish content to the dial glass, but it is less noticeable in real life than it is in the photo. I may put another coat of green paint on to the ends of the glass - that should almost certainly have an effect - but in doing that I don't want to reduce the level of scale illumination too much, though there is some movement available in that respect.

But wait... disaster.. the left hand speaker has just decided to go almost dead on FM stereo! On AM both speakers work, as they do on the other inputs using a 'wet finger' test. Also, switching to mono on FM brings in both speakers. What area does that narrow the fault down to? If I turn the balance fully to the left (the faulty side) and wind the wick up full, I can just about hear the FM broadcast.

[Edward Huggins]

The stereo decoder maybe? Edward

[sp10mk11]

arghhh well many years ago I had one of these with the same fault. it turned out to be an open circuit resistor (you will need the diagram to follow the audio signal out), but on the picture the big red filter thingy has a two rows of resistors in front of it and from what I remember it was one of those.

So the meters are using the original bulbs not LEDs.
Yes carry with the colouring tests I am very interested, I am enjoying this thread a lot

Gary

[stevehertz]

I'll have to get the cct diag out and see if I can figure out what's going on. I'm not good on at fault finding on solid state RF stuff. Plus the service data that I have is incomplete and of (visually) very poor quality.

Yes Gary, the meters are surrounded by a tin box with a frontal translucent green filter, and back illuminated with a single bulb that is one of the original incandescent festoons. The new LED bulbs each side of the dial glass give off a bright, shimmering, bluish tinged light that is doubtless skewing the colour a tad. The incandescents give more of a warm tinge.

I'm annoyed at this new fault though! Talk about just as you are about to replace the last screw on the cover..