It might be worth overriding that pin by shorting out the cap that connects to it.
Another thought. I see it has an old fashioned battery backup. Try removing the batteries and then discharge the cap with a 1k for 30 minutes or so. Then switch on without the batteries fitted and see if its any different.
Another thought. I see it has an old fashioned battery backup. Try removing the batteries and then discharge the cap with a 1k for 30 minutes or so. Then switch on without the batteries fitted and see if its any different.
Attachments
It doesn't have batteries it has 3 x 3.3 farad 1.8v super caps. The front 12v light isn't coming on although the bulb is still OK,I cant find why yet but I'm thinking it might be related to the stereo mono switch? Its 12 o'clock midnight here now and Id better get some shut-eye.
Hmmm... it might still be worth discharging those... well what I would do is just remove one (or a series feed from one) to remove totally the backup supply. A dodgy supply like you have had could well have spiked the microprocessor and caused some internal latchup that only removal of the supply would correct.
A word of caution... with user removable batteries there is no issue of any unique setting being lost permanently. With inbuilt caps some equipment can lose vital regional settings (such as AM channel spacing of either 9 or 10kHz) when the backup supply is removed. Its very to come across equipment like that but it does happen.
A word of caution... with user removable batteries there is no issue of any unique setting being lost permanently. With inbuilt caps some equipment can lose vital regional settings (such as AM channel spacing of either 9 or 10kHz) when the backup supply is removed. Its very to come across equipment like that but it does happen.
Ive taken out the first super cap to cut off any voltage.When I took it out one of its pins literally fell out and I could see the next one was leaking electrolyte,so it looks like they weren't working anyway? I still cant get the stereo light working,Ive turned the VR 301 in very small increments and waited about 5 seconds then turned it again etc...etc...Ive spent about an hour altogether trying to get it working. The 6.3v PLL Quartz lock light that isn't working has 3v on one wire and 1.40v on the other and 1.74v across them both? Looks like I might have to get a service manual!
I wondered as much with the caps, generally speaking they always seemed to fail or worse.
Where to go next with it... I'd be reluctant to condemn any of the IC's as a first line of attack. One thought... sorry, have to mention it 🙂 is the incoming signal high enough to operate the stereo decoder ? outside aerial with a good level.
If I had the unit in front of me I think I would look at the obvious failure, the 12 volt supply and that resistor. I would be inclined to override the 12 volt with a variable PSU and just see if the alignment of the tuner was altered by changing the supply. IF (IF as in intermediate frequency) amplifiers and oscillators will vary their alignment a little with changes in supply. Its something to look at. I would also look with a scope at the signal going into the decoder chip and make sure the low level 19kHz pilot tone was present (which the decoder needs to phase lock and regenerate its own locally derived 19/38kHz signal)
If you put the presets back to the original settings then another trick is to use your fingers on PCB around the tuned circuits and so on and try and see if you can swing the alignment by the resistance/capacitance of the presence of your finger. Its a crude trick but can get results in showing where problems might be.
Where to go next with it... I'd be reluctant to condemn any of the IC's as a first line of attack. One thought... sorry, have to mention it 🙂 is the incoming signal high enough to operate the stereo decoder ? outside aerial with a good level.
If I had the unit in front of me I think I would look at the obvious failure, the 12 volt supply and that resistor. I would be inclined to override the 12 volt with a variable PSU and just see if the alignment of the tuner was altered by changing the supply. IF (IF as in intermediate frequency) amplifiers and oscillators will vary their alignment a little with changes in supply. Its something to look at. I would also look with a scope at the signal going into the decoder chip and make sure the low level 19kHz pilot tone was present (which the decoder needs to phase lock and regenerate its own locally derived 19/38kHz signal)
If you put the presets back to the original settings then another trick is to use your fingers on PCB around the tuned circuits and so on and try and see if you can swing the alignment by the resistance/capacitance of the presence of your finger. Its a crude trick but can get results in showing where problems might be.
I'm using the same antenna on a Pioneer TX-410 and it picks up stereo no problems? Ive checked around the board and its getting 11.9v-12v alright. The decoder chip is getting 19khz OK on pin 9 but no stereo light? 1.40v on pin 16? This is getting weird?
Attachments
Last edited:
Can you detect 19kHz on the input at pin 2 ?
That's an audio input but the transmitted pilot tone should be detectable although it might be hard to winkle out on a scope. You would likely see it in the silences within a stereo transmission.
That's an audio input but the transmitted pilot tone should be detectable although it might be hard to winkle out on a scope. You would likely see it in the silences within a stereo transmission.
No I cant detect anything on pin 2? I used the same frequency counter that I used on pin 9.Ive got a scope but its a pain to use.I'm listening to the tuner now and it sounds excellent except for there being no stereo,its crystal clear ,no distortion no hum. I got 65.8 to 65.9khz on pin 15?
Last edited:
The pilot tone has to be present on the incoming audio for the decoder chip to lock. The 19kHz you are picking up is just the oscillator. Is it exactly 19.00000kHz (which would indicate lock) or is it off a little and adjustable with the preset. If it adjusts and the counter is accurate then set it to 19.00000
Its exactly 19.00000khz.That PLL quartz lock light not working must have something to do with it but what?
Last edited:
OK. If you detune the radio does the 19.0000 wander away (go out of lock). To be exactly correct suggests it is working.
I de-tuned it until I could just hear the station over the static and it was still on 19.00000khz.
And do you get 19.000 with it totally detuned between stations ? I would have thought it would have free run with no incoming transmission.
Very odd. It sounds like its locking OK to the incoming transmission.
And again... sorry to ask 🙂 your sure that the audio has no stereo content when listened too despite what the indicator shows... had to ask 😀
I'm reluctant to condemn chips, its 99% of the time something else, however......
So that leaves pin 16. If you switch to mono on the front (can you do that on this model ?) does the 19kHz wander again ? which it should I would think.
After all that there's not much else left.
And again... sorry to ask 🙂 your sure that the audio has no stereo content when listened too despite what the indicator shows... had to ask 😀
I'm reluctant to condemn chips, its 99% of the time something else, however......
So that leaves pin 16. If you switch to mono on the front (can you do that on this model ?) does the 19kHz wander again ? which it should I would think.
After all that there's not much else left.
Yes it has a mono switch on the front and it wanders off 19khz when de-tuned between mono stations. I'm definitely trying to get the stereo light tuned in on stereo stations LOL.Ive checked by switching to mono on a stereo station and it doesn't change anything at all? It still sounds the same? It must be a cold solder joint or something like that,if I find it Ill let you know what it was.Thanks for all the advice and suggestions Mooly Ive learnt quite a bit from this as well.Some-one has been at this tuner before me so they might have soldered a wire in the wrong place or something so Ill get a service manual and check it out.Thanks again mate,its appreciated.
No problem, you're very welcome 🙂 however I don't really know what else to suggest next to you on this one.
If its been worked on then I suppose anything could have happened. The stereo light not illuminating might be one to work on although looking at the diagram it multiplexed into the display so there isn't an easy way to delve into that.
On the manual I have there is a weird "allocation" switch. Does yours have that. What does that do ?
If its been worked on then I suppose anything could have happened. The stereo light not illuminating might be one to work on although looking at the diagram it multiplexed into the display so there isn't an easy way to delve into that.
On the manual I have there is a weird "allocation" switch. Does yours have that. What does that do ?
This model doesn't have that,it just has the power on switch in its place? I noticed that the quartz locked PLL light is working now.On the stereo demodulator chip datasheet it says that pin 16 is supposed to be 1.40v in mono.Thats what I'm getting,so its not switching into stereo for the light to come on.Ill upload it, you will probably make more sense out of it than me?
Attachments
What happens if you short pin 16 to ground to pull it low ? I can't see anything obvious on the diagram that could actually do that and yet that could by implication be the voltage needed for stereo. Big question is whether its derived internally in the chip or whether its an input to the chip. I can only see means of increasing the voltage on pin 16 via the diode gating from the various (electronic) switches. Nothing that could pull it right down.
Worth a try and a listen to see if you get stereo.
Worth a try and a listen to see if you get stereo.
Yaaaaay! Stereo!!! Hang on it wont work again but it did the first time??? Its flickering on and off so it must need tuning in?
Last edited:
- Status
- Not open for further replies.