Did anyone ever find a schematic or a service manual for this model?
Yamaha designs do have many things in common, like parts, esp for the same series.
What else is similar? so we can refer to it. A TX-550, has the LM7000 PLL
Most yamaha's use the same Mitsubishi pre-scaler IC. Looks like LM7000 has a pre-scaler built in.
Rick
Yamaha designs do have many things in common, like parts, esp for the same series.
What else is similar? so we can refer to it. A TX-550, has the LM7000 PLL
Most yamaha's use the same Mitsubishi pre-scaler IC. Looks like LM7000 has a pre-scaler built in.
Rick
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Post #67 (I keep having to look back 
) mentioned a real difference and so obviously the correct manual would be a big help.
Yamaha TX540 tuner not tuning
The commonality (or lack of) between FM/AM is a good point and post #1 mentions AM not working as well. I wonder if the tuner has seen some high voltage event on the aerial downlead in the past...
) mentioned a real difference and so obviously the correct manual would be a big help.Yamaha TX540 tuner not tuning
The commonality (or lack of) between FM/AM is a good point and post #1 mentions AM not working as well. I wonder if the tuner has seen some high voltage event on the aerial downlead in the past...
Hi Glenn,
Time to remove the tuner pack from the PCB, then inspect the bottom connections on the tuner pack. If everything looks good, time to remove the shields over the oscillator area. There will be one or two transistors in that section. However, they might also put the mixer in there too. Put your meter in diode test mode and look for shorted or oprn junctions. Because this is an RF circuit, RF transformers will look like a direct short circuit, so you will have to remove the transistors to test them. Pull them out one at a time and reinsert when you have tested and on to the next. It really helps to take a picture or two before you start so you can see which way the transistor is installed in case you are interrupted (or you just forget like me).
Let us know what you find. You'll probably be at a stage where you only need a transistor to get the tuner working. This is excellent training.
-Chris
Time to remove the tuner pack from the PCB, then inspect the bottom connections on the tuner pack. If everything looks good, time to remove the shields over the oscillator area. There will be one or two transistors in that section. However, they might also put the mixer in there too. Put your meter in diode test mode and look for shorted or oprn junctions. Because this is an RF circuit, RF transformers will look like a direct short circuit, so you will have to remove the transistors to test them. Pull them out one at a time and reinsert when you have tested and on to the next. It really helps to take a picture or two before you start so you can see which way the transistor is installed in case you are interrupted (or you just forget like me).
Let us know what you find. You'll probably be at a stage where you only need a transistor to get the tuner working. This is excellent training.
-Chris
Thanks Chris. I will delve into the tuner pack. I always take photos before I pull things out. Rsavas, I never got a hold of a schematic for this model. I did locate a schematic on one of the radio specialty sites but did not manage to successfully download it. So, we have been working from the TX550 schematic. Glenn
TX-550 sch shows two FM tuner models, do the part numbers match the one you have?
I am not so sure of removing the FM tuner pack. The AM does not work either so you could just as well figure that out and it has nothing to do with the FM pack.
Removing the FM pack probably will not make the AM work so ...
Ask yourself what is common to both AM & FM circuits.
I am not so sure of removing the FM tuner pack. The AM does not work either so you could just as well figure that out and it has nothing to do with the FM pack.
Removing the FM pack probably will not make the AM work so ...
Ask yourself what is common to both AM & FM circuits.
Rsvas, just saw you last post. It is the VI12260. Have already acted on Chris's last post and removed the tuner pack. That was relatively easy using solder wick. Have also removed the metal case. Now that was a tricky proposition. Many solder points. Anyway, lots of transistors in there. Also some epoxy at one corner covering some components. Not sure where to start. Near osc out pin? Can post photo if you wish. Glenn
I missed that one, so continue per Chris's advise.
A pic of the FM inside would help locate parts.
The local oscillator is Tr4 and Tr3 is the buffer for the LO out to the LM7000.
You can test it on the bench, you just need to power from ~12VDC and you can use the same supply for the varactor tuning V. GND of course.
Check bias voltages for Tr3,4
Tr1 is the RF amp, Tr2 is the mixer, Tr6,7 make the Rf level detector for the AGC V to the 2nd gate of Tr1. As RF level increases gate2 V decreases.
And me
I looked back in the thread and couldn't just spot anything about AM working. Post #1 mentioned it was non operational.
A big problem we have is in not having the correct diagram for the tuner front end...
Third time lucky. Found the post where you mentioned AM. Don't know how I kept missing that one:
So your tuner has the one can that has both AM/FM sections in it and these use a common tuning voltage line (Vt). So we know the tuning line isn't being pulled down in the can as it works on AM.
This is odd because the local oscillator not running on FM appears to be a definite measurable issue. What is weird is that the tuner doesn't work normally on AM on its own.
Thinking out loud now I guess there could be differences in the way the LM7000 is configured between models. What is stopping it working normally on AM?
The LM7000 takes the FM local oscillator signal in on pin 14 (the one that's missing), it takes the AM local osc in on pin 13... does it need that when tuning manually? What does it do in this state... maybe nothing... nothing as far as I can see...
Question.
When you tuned the pot manually and if you had AM selected on the tuner, did the tuner frequency display change as you altered the pot?
I'm just wondering whether we have two issues here which is unlikely, or whether we looking in the wrong direction now. I wonder what the amplitude of the local osc FM signal should be... are we missing it when in fact it is perhaps present?
Third time lucky. Found the post where you mentioned AM. Don't know how I kept missing that one:
So your tuner has the one can that has both AM/FM sections in it and these use a common tuning voltage line (Vt). So we know the tuning line isn't being pulled down in the can as it works on AM.
This is odd because the local oscillator not running on FM appears to be a definite measurable issue. What is weird is that the tuner doesn't work normally on AM on its own.
Thinking out loud now
I guess there could be differences in the way the LM7000 is configured between models. What is stopping it working normally on AM?The LM7000 takes the FM local oscillator signal in on pin 14 (the one that's missing), it takes the AM local osc in on pin 13... does it need that when tuning manually? What does it do in this state... maybe nothing... nothing as far as I can see...
Question.
When you tuned the pot manually and if you had AM selected on the tuner, did the tuner frequency display change as you altered the pot?
I'm just wondering whether we have two issues here which is unlikely, or whether we looking in the wrong direction now. I wonder what the amplitude of the local osc FM signal should be... are we missing it when in fact it is perhaps present?
The Sanyo LM7000 spec says that, if I look, 0.1 to 1.5V rms for both Am & Fm inputs.
Looking at the parts spec tells you in some cases more than the service manual does or in better terms.
I am going to have to refresh my memory or learn about the LA1266 part. I have the spec in my lib, so who knows what I was using it for, my memory fails me
Excellent spec, app circuit and all, lots to learn.
In other forums I have talked about using one tuner to troubleshoot another tuner, if you do not have a RF Sig gen. Take the IF out of a known good tuner Front end and inject it into the IF of the one under test, with it disconnect from its own RF FE which is also in ? Vise versa as well.
Good luck in tuner camp
Rick
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