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

[stevehertz]

Regarding a Sony STR-6900 receiver I need to tackle the following issues if anyone can help please.

There is slippage of the drive cord around the tuning knob drive shaft. While the cord does not appear to be in the best of conditions and is maybe just a tad loose, on inspection the tuning cap itself is quite stiff when turned manually and I get the impression it would work ok if there was not so much resistance at this point. The other, rotating nylon supports that the cord passes around I have addressed and lubed lightly with a drop of silicon lube, so they're ok. I have lubed the tuning cap as follows. Regarding the short 'axle' length on the right hand side, I have given it a few drops of very light machine oil at either end of the casting. Where the long brass rod that supports the vanes passes through screens I have lightly lubed those places with Servisol as I believe there's also an electrical connection there too. But on the left there's a shielded, soldered 'tin box', and I don't know what's going on in there, if that's the source of the tightness?

Now, looking at Youtube videos, the main tuning scale should illuminate a soft green colour. Mine has obviously been 'got at' as it only glows 'white' and that only from the left hand side. Has a green filter of some kind been removed? What's going on? Clearly there's a lamp out on the right hand side. See photo taken in the dark of mine, and the other (not mine) of how it should look.

Finally, the channel balance is out. The balance control has to be set at 3 o'clock (not 12 o'clock) to achieve equal volume from both channels. Sounds like an audio amplification issue on one channel to me, or is it a simple matter of tweaking an internal channel balance pot? - if indeed such a thing exists, or similarly, a channel gain pot?

[vidjoman]

Many Japanese radio dial lamps were coated with a clear blue or green paint to give the coloured lighting. Some had a coloured silicon sleeve. I expect the originals have been replaced with plain ordinary lamps.

[stevehertz]

Ahh, thanks Vidjoman. So I'll have to experiment in that respect. Hopefully the right hand (faulty) dial lamp will still be present and I can see how it should be.

[Nickthedentist]

Originally Posted by stevehertz

Finally, the channel balance is out. The balance control has to be set at 3 o'clock (not 12 o'clock) to achieve equal volume from both channels. Sounds like an audio amplification issue on one channel to me, or is it a simple matter of tweaking an internal channel balance pot? - if indeed such a thing exists, or similarly, a channel gain pot?

I'd be amazed if it's just adjustment required. Some component will no doubt have changed value, reduced in gain, gone o/c or s/c etc.

The good news is that with a stereo amp, you can work your way from input to output, comparing the two channels to see where the discrepancy starts.

Do you have a circuit diagram, and, ideally, a scope?

N.

[stevehertz]

Nick, I have some incomplete service information that was free off the net, and I haven't checked yet to see what is there and what is missing; I need to do that. Yes I have a scope. I suppose I can inject my test tone generator at 1k into the aux socket and 'channel vs channel' check what's happening, looking for signal level anomalies. The trouble is, big hifi receivers of this age/genre often have massive access problems wrt servicing, you have to disassemble them, unsolder boards, even remove drive cords and assemblies.. and then of course how do you operate the set?! Yes I know, extend leads and all that. Not for the faint hearted. Why do I take on these things... ?

[Nickthedentist]

I know what you mean, but you can probably work out what's wrong without massive disassembly, though this may be required to effect a repair.

Also look for signs of previous repair work, especially that of our friend Billy Bodger!

Good luck with it!

Nick.

[sp10mk11]

Hello Steve
I can shed a little light on the display colour.
The glass that has all the printed frequency bands etc has transparent green glass paint applied to the ends this is partially covered by the rubber mounting end pieces, so the white light shines through the green painted end and you get your green display
The printing after all these years can be very brittle and flakey so do not wash it! the lettering etc will come off
It sounds to me as if it needs a complete strip and service, you are right to clean out the short shaft these have grease on them from new and they get very sticky after a many years, the rest of tuning cord pulleys etc benefit from a clean and lubing as does of course the flywheel assisted tuning knob.
I always found these and others from that Sony range easy to work on and strip, there are some soldered wires but there are also a lot of plug in connectors between the boards.
These were the then top of that range model, and this model stood out head and shoulders above the lower models sonically, a very good sounding piece of equipment.
As you will know it uses power amp blocks, try not to blow them as they either unattainable or stupidly expensive.
I have tried using LED lights in these but not with much success, maybe newer ones are better
Good luck
Gary

[stevehertz]

Originally Posted by sp10mk11

Hello Steve
I can shed a little light on the display colour.
The glass that has all the printed frequency bands etc has transparent green glass paint applied to the ends this is partially covered by the rubber mounting end pieces, so the white light shines through the green painted end and you get your green display

Thanks for your input Gary. So, based on my photos, what do you reckon could be the problem with mine?

[stevehertz]

Ah.. searching the net I came across this from - a German writer I think - translation came up as:
"The scale had on both sides a light green color filter made ​​of plastic. When removing the dial plate of the color filter crumbled, however, to expect as much different. The green color of the scale I still can get by I have brushes the edges of the dial with a green light color."

Looks like you basically have to 'paint' the edge/end of the scale green. Any ideas for an actual name/type of paint? Obviously the lamp has to shine through it.

[Nickthedentist]

Green permanent marker pen? Or translucent nail varnish?

[vidjoman]

You can get transparent paint from model shops and from craft shops in small pots for making stained glass windows.

[stevehertz]

Thanks guys, that's given me some ideas to work on. I'll have to dismantle the control panel assembly on the receiver to see what's actually going on, what bulbs I need etc. I've located some transparent green paint online that is suitable for use on plastics - some are described as being only?) for use on glass and metal.

[Radio Wrangler]

If the bulbs are festoon ones, I recently bought a bunch of LED replacement ones for the Revox B261 I'm working on. From Farnell, USA, they were expensive, but good. The revox bulbs were 35v types so hard to get. The LED jobs covered 10-30v so the pair were re-wired in series and I now have a bright display. and a lot less heat which is what will have cooked your filters.

David

[sp10mk11]

I bought the glass paint from an art shop and I painted it on the ends of the glass, mine did not have the green filter plastics on it so maybe Sony changed there mind about this.


Just out of interest the bulbs are a sort of fat festoon, 330ma 11v, I have searched high and low for them but never been able to get any, they were used in the rest of that range.

On my TA-5650 tuner I put in 12v 300ma bulbs in run off a tiny separate 12v transformer which gives adequate light, the 11v supply just does not drive them well enough so the display is dark, the light you get from LEDs is good but it doesn't spread like a fuse bulb so you get bright spots I found this on the tuning panel and the meters.

[stevehertz]

Originally Posted by sp10mk11

Just out of interest the bulbs are a sort of fat festoon, 330ma 11v, I have searched high and low for them but never been able to get any, they were used in the rest of that range.

On my TA-5650 tuner I put in 12v 300ma bulbs in run off a tiny separate 12v transformer which gives adequate light, the 11v supply just does not drive them well enough so the display is dark, the light you get from LEDs is good but it doesn't spread like a fuse bulb so you get bright spots I found this on the tuning panel and the meters.

Valuable info, thanks. I have the STR-6800 service data, but strangely, the info re the bulbs does not seem to be there. However I also have the data for the STR-4800 and it's in there - see photo attached. Did you try Sony spares with that part number? The data describes PL1 - PL3 as 11v, 360mA. Do they screw in? What's their physical format? I'm not sure what a festoon lamp looks like although I've heard the word many times!

I'm surprised that the 12v ones you tried were inadequate when driven by 11v? I'm thinking that maybe even if the illumination is low, then for this purpose (subtle lighting) it would be ok? But you've tried it, I haven't!

[Brian R Pateman]

Festoon lamp;

[stevehertz]

Cheers Brian. I've done a bit more digging around on the net and found a photo of the actual bulb - attached. Seems very much as though it's not stocked by anyone any more. So either someone may have a couple hanging around - a repair shop or an individual - or I'll have to improvise as has been suggested.

[Radio Wrangler]

Brian's photo is of that rare beastie, a virgin festoon bulb. All the ones I seem to see are blown. For some reason festoons seem to have significantly shorter lives than single-ended bulbs.

How long a festoon do you need? I'm not at home at the moment, but I do have a couple of the Farnell LED ones because I bought a couple of spares when I bought a set for the revox. If they're close I could lend you a couple to try. They're about £3 each from Farnell, but an extra £15 per order to get from the states. It made sense for me to get spares when I bit the bullet on that one.

David

[stevehertz]

David, kind offer and I'll get back to you when I've dived into the set. I'm tied up on another project at the moment (plus the requirements of simply existing - as we all know!), but hopefully I'll get back to you soon. See pic of actual bulb in my previous post.

[sp10mk11]

Hello Steve

Yes that's the bulb and 360ma as you say (foggy memory).
this is a bug bear to me with any of this range of Sony equipment that used these bulbs.
But as I say I did get round it.
I wish you luck because the 6800 is a great sounding and performing piece of kit.
Gary

Off topic a bit, the 25 watt bulb blew in the fridge, didn't have one, rummaged around and found an 8 watt LED same screw in fitting, went straight in and works a treat.