Does anyone have the service manual for this set? It's got a frame linearity fault, which has improved since I replaced C462, which had popped it's bottom off. I did find a snippet of the schematic Chris posted when Wayne was working on one, but it seems to bear little resemblance to the set I have in front of me.
Any clues?
TIA,
Doz.
after much messing about I found the culprit, it's a tant, very thermally unstable. The issue is, it's marked with three dots, a slanted T and 35v ... so what's the value? I've tried 4.7u which cause the oscillator to run super slow, and 0.47 (these are the only two values I have in 35V!) , which works, but leaves low height. It's marked C454 on the PCB
After further investigations, the tant proved out at 1uF. Replacement made zero difference (I used to 0.47's in parrallel). Freezing and warming the area has proved the SCS , 3SF11 is causing the issue. It appears to be made from unobtainium
BR101 or BRY39 might be possible replacement? Radiomusem shows the internals as a PNP and NPN transistor and NTE239 as an equivalent. I'm presuming your set is much different from the circuit as I don't see an SCS anywhere.
John.
Hugely different from that schematic. Thanks for the suggestionsof BR101, or BRY39.. nothing to lose !
Well, a new BRY39 went in, and it's no longer thermal. It's not right by any means. If I get the frame adjusted right at the bottom, I can't get enough height. Chris is finding out the rest of the 262 schematic, which seems correct bar a few component numbers here and there.
After our erstwhile leader provided a better, if not entirely correct schematic, the HT to the field output stage was low, traced rapidly to an O/C capacitor, C456 (on the diagram) which is C463 on the set I have. Set the frame up, and sat down with the set on test , and a few minutes later , there's a few crackles on the sound, followed by no sound. A poke round the AD421D shows everything normal, but no output ... damn. I've ordered one.
Incidentally, freezing and warming the new SCS made zero difference, even with C456 O/C .... a garden path fault.
These were excellent sets, The place I first worked for when I left school had loads, they sold so many Nat-Pan products they won 'dealer of the year' (or something like that.) The Prize? A brand new van sign-written in Panasonic Decals! I left in '81 and had never seen a faulty one!
On with the sound.... A replacement AN241D sourced and fitted - no change. I knew in the back of my mind this would be the case.
Injecting a bit of audio into pin 14 worked, as did injecting it into Pin 8 (unsurprisingly) The block marked "volume control" must be some form of VCA, and isn't used in this set (the volume control just follows the preamp, in the conventional analogue manner). The voltages around the IC are nominal.
Checked for IF at A7, yep, that's there. Then checked for IF on pin 1, yep. Checked on pin 2, and as soon as the probe touched the pin, the sound was restored! What?? After a few minutes, it went back off again...
HELP.
T201 intermittent or O/C?
Oh, and it's repeatable....
forgot to post the schematic!
Pin 2 is GND! Did you check continuity to main GND?
Sounds like something floating to me.
Does it connect thru the can of the transformer by any chance? You can have solder joints that look perfect but aren't.
Had the same problem on a Kriesler CTV many years back.
@irob2345 Pin 2 isn't ground ! There's no junction between C209 and pin 2. Pin2 is also shown as 1.8V. I've been round the whole area with a hot iron, still the same ....
I agree though.. it does sound like something floating
An interesting fault! I was thinking along the lines of a dodgy muting circuit, but it doesn’t look like there is anything like that in there.. I would have thought if the coil was intermittently O/C then giving it a tap on the side of the can would have made it come and go, and that when the probe was taken away from pin 2 then the sound would go straight off rather than stay on for a short while. Could it be something around the volume control part of the chip? Maybe when you tickle it with the probe it kicks something into working, possibly worth looking at the components connected to pins 6 and 7 just in case?
C209 looks like it's grounding Pin 2 but of course that would make no sense as it's .047uF
the diagram's not entirely well drawn, but there's no junction shown on the bottom of c209C209 looks like it's grounding Pin 2 but of course that would make no sense as it's .047uF
It was T201. Couldn't see a way to get it apart and see if where there was any damage, so got the legs good'n'hot with the iron, and it's been running great for an hour or so now 🙂
the diagram's not entirely well drawn, but there's no junction shown on the bottom of c209C209 looks like it's grounding Pin 2 but of course that would make no sense as it's .047uF
The size of the dot showing the connection of C209 to pin 1 of the IC compared to the near-absence of a dot as it passes through the wire from the transformer to pin 2 looks clear enough to me.
Fetched T201 out, as it seemed to be the issue. I didn't fancy disassembling it, so cooked each leg with the iron a bit. Fitted it back in, sound restored. It's been working well for hours now.
