Yes ,I was thinking if something like that would work.
Another test that needs to be done is to take a frequency counter reading of the LO and compare it to the display frequency plus the IF frequency to see if it is acutualy off by .1mhz ,just to be sure.
Another thought that comes to mind is what happens when it is in manual mode?
Does the frequency display increment with every tuning incerment or every other pressing of the tuning button?
Does the display show even and odd numbers?
Inside the there are two switches ,one is for a narrow or wide bandwidth setting and the other is for 50khz incerments instead of 100khz increments.
In order to detremine if the PLL is sending the proper data to the display driver this requires a scope and can be done quite simply.
And I'm not exactly sure the function of L305 for a centering voltage as I am currently tracing that line. jer
Another test that needs to be done is to take a frequency counter reading of the LO and compare it to the display frequency plus the IF frequency to see if it is acutualy off by .1mhz ,just to be sure.
Another thought that comes to mind is what happens when it is in manual mode?
Does the frequency display increment with every tuning incerment or every other pressing of the tuning button?
Does the display show even and odd numbers?
Inside the there are two switches ,one is for a narrow or wide bandwidth setting and the other is for 50khz incerments instead of 100khz increments.
In order to detremine if the PLL is sending the proper data to the display driver this requires a scope and can be done quite simply.
And I'm not exactly sure the function of L305 for a centering voltage as I am currently tracing that line. jer
Hi jer,
A man without an oscilloscope is very unlikely to have a frequency counter. It's so sad. Given that situation, he needs a friend with gear.
-Chris
A man without an oscilloscope is very unlikely to have a frequency counter. It's so sad. Given that situation, he needs a friend with gear.
Without a schematic, I can only assume you are talking about centering the frequency (balancing the transformer at 10.7 MHz) for 0.0 mV. That adjustment can be a pain if the adjustment is too touchy. As I recall, no problem with the TA series of receivers. After that one, you get to play with the other winding and adjust for the lowest THD. This is a critical adjustment as well. So now you also need an FM stereo generator that is more accurate than a Heathkit (and many others), along with a distortion analyzer. The levels change too, so something like an HP 339A or 8903A would be very helpful. Using ones that require you to set the reference level is a pain. Did that for years.
-Chris
I was just studying the data sheet to LA1235 fm detector chip.
This coil (L305) is frequeny tuning null adjustment and acorrding to the alignement procedure it is to be adjusted with a signal generator at 98mhz until 0v across a resistor.
This is the AFC circuit.
The signal from this circuit does not feed directly into the PLL,But it will effect the center point of the peak signal strength that tells the PLL to stop searching and/or lock.
He said that he had adjusted this but under what conditions? jer
This coil (L305) is frequeny tuning null adjustment and acorrding to the alignement procedure it is to be adjusted with a signal generator at 98mhz until 0v across a resistor.
This is the AFC circuit.
The signal from this circuit does not feed directly into the PLL,But it will effect the center point of the peak signal strength that tells the PLL to stop searching and/or lock.
He said that he had adjusted this but under what conditions? jer
Oh yes, I ,understand I used to mess with CBradios and I have the B&K 40 channel alignment signal generator.
I once had a Kenwood 940/AT the got smashed in a nasty arguement between two idiots (my friend and I).
I was told by many many people and techs that even if I had gotten it all glued back together that there would be a very slim chance that I could get it to work again and that its performace would never be the same.
So I kept it, but oneday when I wasn't around my mother thought it was just heap of something that I tore apart and threw it out (sad,sad,sad)!
I paid $1800 (I think,maybe more) for it used In 1990 and now I find them for $500 on ebay.
Man,that was one beutiful piece of equipment as mine was modified to transmit continuosly from 1mhz to 30mhz.
What great signal generator it was.
I hope too someday replace it. jer
I once had a Kenwood 940/AT the got smashed in a nasty arguement between two idiots (my friend and I).
I was told by many many people and techs that even if I had gotten it all glued back together that there would be a very slim chance that I could get it to work again and that its performace would never be the same.
So I kept it, but oneday when I wasn't around my mother thought it was just heap of something that I tore apart and threw it out (sad,sad,sad)!
I paid $1800 (I think,maybe more) for it used In 1990 and now I find them for $500 on ebay.
Man,that was one beutiful piece of equipment as mine was modified to transmit continuosly from 1mhz to 30mhz.
What great signal generator it was.
I hope too someday replace it. jer
I had some time to test some more things this morning. I wasn't sure if you wanted me to check voltages on the PLL synthesizer on the logic board or the PLL demodulator on the main board. I checked the synthesizer as it's much easier to get to. All of the pins had voltages that were very close to the schematic. None of them were significantly off. Pins connected to front button functions behaved as they should when buttons were pressed. I tested voltage on everything on the tuner pcb that was labeled on the schematic. Nothing was off spec. Unfortunately, over half of the transistors have no voltage specs on the schematic, so I had no way of testing those. Vt on the tuner front end (pin 5) ranged from 2.9v -21.1 through the frequency range. The bandwidth selector switches are not present on U.S. destined models. In manual mode, the display increments .1mhz with every press of the button, showing even and odd numbers.
Here are a couple new observations that may help point us in the right direction:
1) Lock and stereo will only happen in auto mode, and is displayed .1 mhz too high. In manual mode, lock will occur when the display is .1 mhz too high, but it will not go stereo under any circumstance. I don't know if it is designed this way, but there is no way to listen in stereo in the manual tuning mode. The stereo mode was confirmed while listening with headphones.
2) Even though lock and stereo occur when the display is .1 mhz high, the signal strength is slightly stronger when the display is on the correct frequency and there is no stereo or lock. This is observed on the signal strength meter and measuring voltage on pin 8 of U601.
My Fluke 87 has a frequency counter. Let me know if I can utilize it on this project. I'll look into getting a scope. I know it's a great tool, even if only used on a hobbyist level. I'd love to get a fluke scopemeter. Gathering the funds would be the challenge...
Thanks, and keep em coming!
Here are a couple new observations that may help point us in the right direction:
1) Lock and stereo will only happen in auto mode, and is displayed .1 mhz too high. In manual mode, lock will occur when the display is .1 mhz too high, but it will not go stereo under any circumstance. I don't know if it is designed this way, but there is no way to listen in stereo in the manual tuning mode. The stereo mode was confirmed while listening with headphones.
2) Even though lock and stereo occur when the display is .1 mhz high, the signal strength is slightly stronger when the display is on the correct frequency and there is no stereo or lock. This is observed on the signal strength meter and measuring voltage on pin 8 of U601.
My Fluke 87 has a frequency counter. Let me know if I can utilize it on this project. I'll look into getting a scope. I know it's a great tool, even if only used on a hobbyist level. I'd love to get a fluke scopemeter. Gathering the funds would be the challenge...
Thanks, and keep em coming!
Jhanko,The FLUKE 87 only has a maximum frequency measurement of 200khz and you need one that goes to at least 120mhz to measure the LO frequency.
Stereo mode is disabled when in manual tuning (this why I dislike digital tuners).
The stop search signal originates from pin 1 of U601 signal level baragraph display driver then buffered and fed directly to pin 33 of the PLL which is the stop scan input.
The level adjust for this signal is VR301 it is possible that this my be a bit to high causing the PLL to stop before it is supposed to.
My question is does it stop at 93.2 when searching up to the frequency and vice versa when searching down to the designated frequency?
Or is it different according to search direction?
what happens when you manualy tune to 93.1mhz and then switch to auto to get stereo?
Does it mute or does it display locked and stereo?
If it mutes then there could be a misadjustment of L305 and/or VR302 mute level control.
There is a very fine balance between these two adjustments.
When you said that you had adjusted L305 what was the exact procedure that you used?
The manual is not very detailed about these adjustments and what they do although I haven't compleatly read every procedure yet.
The lock light is derived from this signal and the in stereo mode signal and the PLL causing it to unmute.
If you google up the LA1235 datasheet it is a 12 page document and explains the operation of this circuit in detail and you should give it a read in order to understand what is happening.
As well as the PLL TC4147BP ,So far I don't believe there is any thing wrong the the PLL.
Right now I am tracing the mute and stereo/lock system and will keep you posted once I understand it throughly as these signals orginate from the LA1235 fm detector chip. jer
Stereo mode is disabled when in manual tuning (this why I dislike digital tuners).
The stop search signal originates from pin 1 of U601 signal level baragraph display driver then buffered and fed directly to pin 33 of the PLL which is the stop scan input.
The level adjust for this signal is VR301 it is possible that this my be a bit to high causing the PLL to stop before it is supposed to.
My question is does it stop at 93.2 when searching up to the frequency and vice versa when searching down to the designated frequency?
Or is it different according to search direction?
what happens when you manualy tune to 93.1mhz and then switch to auto to get stereo?
Does it mute or does it display locked and stereo?
If it mutes then there could be a misadjustment of L305 and/or VR302 mute level control.
There is a very fine balance between these two adjustments.
When you said that you had adjusted L305 what was the exact procedure that you used?
The manual is not very detailed about these adjustments and what they do although I haven't compleatly read every procedure yet.
The lock light is derived from this signal and the in stereo mode signal and the PLL causing it to unmute.
If you google up the LA1235 datasheet it is a 12 page document and explains the operation of this circuit in detail and you should give it a read in order to understand what is happening.
As well as the PLL TC4147BP ,So far I don't believe there is any thing wrong the the PLL.
Right now I am tracing the mute and stereo/lock system and will keep you posted once I understand it throughly as these signals orginate from the LA1235 fm detector chip. jer
No, I haven't. I did buy a 400mhz scope though. It should arrive in a few days. It should make troubleshooting much easier. I'm sure I'll have more questions when it arrives. I've used a scope before, but never worked on a tuner. My experience is limited to tube guitar amplifiers.
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