Quartz Tuner Reads 10khz Out?

[redrooster]

I have a Kenwood and a Technics digital quartz synthesizer tuner,they both read respectively 10khz and 5khz over the correct frequencey? Is there a way to adjust the reading to the correct readout? They both work OK,its just the readout is wrong?

 

[DF96]

In a 'quartz' tuner isn't the display generated by the PLL chip, so can't be 'wrong'? Maybe the wrong IF offset has been set, as the local osc will be assumed to be 10.7MHz (ish) off from the tuned frequency.

 

[Chris Daly]

I have a Kenwood and a Technics digital quartz synthesizer tuner,they both read respectively 10khz and 5khz over the correct frequencey? Is there a way to adjust the reading to the correct readout? They both work OK,its just the readout is wrong?

I would obtain a schematic, hopefully there is a little trim pot that can be
adjusted related to the display readout. Ah bring back those analogue days
where most of the time it was guesswork where you were on the dial.

With reference to DF96 good advices, using your unused tuner you
should be able to check the 10.7 IF by setting the first tuner say to
88.6 and placing the other tuner very close where at 99.3 - unless there
is a radio station on that frequency the second tuner will pick up a signal
from the the IF of the first tuner.

Cheers / Chris

 

[redrooster]

I would obtain a schematic, hopefully there is a little trim pot that can be
adjusted related to the display readout. Ah bring back those analogue days
where most of the time it was guesswork where you were on the dial.

With reference to DF96 good advices, using your unused tuner you
should be able to check the 10.7 IF by setting the first tuner say to
88.6 and placing the other tuner very close where at 99.3 - unless there
is a radio station on that frequency the second tuner will pick up a signal
from the the IF of the first tuner.

Cheers / Chris

I have the service manual for the Technics tuner. Is this the procedue I use to adjust the readout?

 

[Chris Daly]

Procedure outlined is for adjusting the oscillator which should follow also to be what is displayed,

 

[Extreme_Boky]

I have a Kenwood and a Technics digital quartz synthesizer tuner,they both read respectively 10khz and 5khz over the correct frequencey? Is there a way to adjust the reading to the correct readout? They both work OK,its just the readout is wrong?

I think there are two steps that can be set, one is 9kHz and the other is 10kHz. This can be adjusted... it's a button press combination on power-up, or something like that. Try changing this setting - it may fix the problem you have.

Nick

 

[redrooster]

I think there are two steps that can be set, one is 9kHz and the other is 10kHz. This can be adjusted... it's a button press combination on power-up, or something like that. Try changing this setting - it may fix the problem you have.

Nick

I looked at that but the tuner is exactly 5Khz over what it should be? If the station is 100.50mhz it will show 100.55mhz ?

 

[Extreme_Boky]

Do you get a stable stereo sound when the station is tuned at 100.50MHz (and the display shows 100.55MHz)?

Nick

 

[redrooster]

Do you get a stable stereo sound when the station is tuned at 100.50MHz (and the display shows 100.55MHz)?

Nick

Yes it is a stable stereo sound! It shows its in stereo on the display and quartz locked to the station? So it must be something like a crystal out of wack on the chip that sets the display? I measured the 4.5mhz crystal and got 4.498mhz! Would that be the problem?

 

[Extreme_Boky]

Yes it is a stable stereo sound! It shows its in stereo on the display and quartz locked to the station? So it must be something like a crystal out of wack on the chip that sets the display? I measured the 4.5mhz crystal and got 4.498mhz! Would that be the problem?

I don't think so... What are the tuner model numbers? I may be able to get the service manuals.

Nick

 

[redrooster]

The Technics tuner I have is the ST-S4. I have the ST-S4T service manual,its the only one I could find that was close? The Kenwood is one of those modular models that came out in the 1980s or thereabouts its the RX-235 model with amplifer,dual tapedeck and an FM AM synthesizer tuner.

 

[Extreme_Boky]

IC901 and IC903 drive the FL (display)

IC901: adjust X908 crystal frequency to be 4.5MHz, by turning the trimmer-capacitor CT901. This should fix the problem. (Also, check pin 21 voltage - it should be 4.8V)

IC903: make sure the pin 9 and pin 10 are sitting at -25.3 and 4.8V

Couldn't find anything on Kenwood RX-235, but the logic is the same - so find the FL driver chips that drive FL segments... and do crystal frequency adjustment first.

Nick

 

[redrooster]

IC901 and IC903 drive the FL (display)

IC901: adjust X908 crystal frequency to be 4.5MHz, by turning the trimmer-capacitor CT901. This should fix the problem. (Also, check pin 21 voltage - it should be 4.8V)

IC903: make sure the pin 9 and pin 10 are sitting at -25.3 and 4.8V

Couldn't find anything on Kenwood RX-235, but the logic is the same - so find the FL driver chips that drive FL segments... and do crystal frequency adjustment first.

Nick

Pin 9 and 10 on IC903 read OK 25.01v and 5.20v. There isnt any X908 crystal on this model just the 4.5mhz X901? and no CT901 either? There are two CT trimmers on this board,CT1 and CT201.There are 3 variable resistors as well, VR501,VR301 and VR302.I cant see anything obvious near the ICs to trim?

 

[Mooly]

Try the correct 'technician repair method' as a test

See if a well placed finger on and around each trimmer cap has the desired effect. Thats enough to pull the osc without you having to alter anything.

 

[Willi Studer]

This is local oscillator drifting and is very common in older quartz synthesized tuners. A full alignment procedure requires some exotic equipment which is aligned itself, and also some experience, particularly when it comes to optimal adjustment of dispersion groups.
The other way is to locate the adjustable L coil in the oscillator circuit and align the frequency display to the correct value, trusting that the radio station transmitter is frequency accurate, which is probably the case. I would suggest using plastic screwdriver for this purpose because ferrite cores are very brittle.

 

[redrooster]

This is local oscillator drifting and is very common in older quartz synthesized tuners. A full alignment procedure requires some exotic equipment which is aligned itself, and also some experience, particularly when it comes to optimal adjustment of dispersion groups.
The other way is to locate the adjustable L coil in the oscillator circuit and align the frequency display to the correct value, trusting that the radio station transmitter is frequency accurate, which is probably the case. I would suggest using plastic screwdriver for this purpose because ferrite cores are very brittle.

I think Ill just leave them the way they are,I cant get the correct service manuals so I dont know whats what and I havent got the correct gear either.They work OK now so Ill quit while Im ahead.Thanks for the ideas and suggestions fellas,its appreciated.