Jesan 88-900 erratic output on only 7 high channels

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original45
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Jesan 88-900 erratic output on only 7 high channels

Post by original45 »

Yes another faulty radio I need to pick your brains on . Jesan 88-900 in beautiful condition, everything seems perfect except for a problem with tx power jumping up and down erratically from 4 watts to 2 watts ish.
Really jumping about but seems to be only from channel 33/34 up to channel 40.all other channels are bang on 4 watts and perfectly stable .

You can see it on the tx power needle and on air test confirm it .

If I switch the button to allow the variable tx rf output and lower output to 2 watts it is stable and has good audio too.

Nice little base radio, shame it hasn't a 12v ability also .

Any ideas ? , thank you.
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14CS06
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Re: Jesan 88-900 erratic output on only 7 high channels

Post by 14CS06 »

hello

Another post here

viewtopic.php?f=29&t=20140

Similar to ;
INTEK B-3104AF
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ch25
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Re: Jesan 88-900 erratic output on only 7 high channels

Post by ch25 »

What is voltage on pin 17 of lc7132 on ch30 and 40?
Chris
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original45
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Re: Jesan 88-900 erratic output on only 7 high channels

Post by original45 »

ch25 wrote: 29 Dec 2018, 21:17 What is voltage on pin 17 of lc7132 on ch30 and 40?
Chris
Chris I will study the above schematic courtesy of Claude, thank you Claude and assertion what and where pin 17 is of lc 7132.

Then test v .
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Re: Jesan 88-900 erratic output on only 7 high channels

Post by original45 »

Ok Chris got it , just to confirm procedure please . Do I place possertive probe on 17 and then just earth negative probe on to chassis to earth.

Also do I set mt to 2 v or less or 20v please.

Thank you
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ch25
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Re: Jesan 88-900 erratic output on only 7 high channels

Post by ch25 »

Positive probe to pin 17, negative probe to minus of electrical ground (pin 10). Not chassis ground :)
On channel 40 you should have 3.5V on RX
If not, tune T9 to get that voltage. use plastic screwdriver or toothpick, be careful not to break ferrite core.
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Re: Jesan 88-900 erratic output on only 7 high channels

Post by original45 »

IMG_20181231_122344_894.JPG
Sorry for my delay. The ic chip thing isn't as in schematic and only has 9 pins too.

Image hopefully attached.
Thanks
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ch25
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Re: Jesan 88-900 erratic output on only 7 high channels

Post by ch25 »

Oh man...
Glass window must be covered. Put some sticker on it asap. Light erase chip memory!
Schematic does not represent radio from your photo. Your radio seems to be modded, someone added eeprom chip.
Without proper schematic I can't help.
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Re: Jesan 88-900 erratic output on only 7 high channels

Post by 163TM847 »

The eprom is factory standard i believe it is for the up/dwn channel buttons, I would say the VCO is slightly out of lock, When you monitor yourself on another radio [TX on channel 40 on the Jesan and RX on ch 40 on another working radio] does the monitor radio receive you ?
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Re: Jesan 88-900 erratic output on only 7 high channels

Post by ch25 »

Eeprom is not on the schematic, nor MC145106p. Can be stock, but not on schematic provided.
To check VCO we must know what PLL is used in that radio. Than we can continue.
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original45
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Re: Jesan 88-900 erratic output on only 7 high channels

Post by original45 »

Thanks Chris for trying in any case.
Black spirit , looking at a online YouTube tutorial and his explanation on lock ,the display on front of radio has a lock indication light if I understand it correctly .
As I change channel it is instant as I change .

This problem starts at channel 33 that I can see visually via the signal meter needle.
On 33 if I key up the needle moves so slightly you really have to look hard and close, 34 or moves a fraction more ,35 slightly more and by the time you get to channel 40 the needle when you tx jumps from 2to 4 watts back and forth erratic.
On air radio report about 20 miles away stated my rx signal was bouncing and audio was breaking up.
If I reduce watts out to 2 watts via the rf power ajust it stabilizes both needle and rx signal received and is perfect audio .

Now today I put on a power meter swr meter.
Guess what ? It's moved channels not to high or low but around channel 9 to channel 15 ish .

To be very honest I'm far from knowledgeable and will not ajust touch anything until I'm sure I can do it either by ear ,meter so on.

I will have another test latter just to 're confirm this issue ,but I tried it twice and both times since the meter is inline the fault has changed channel.if I remove meter it's back to channel 33-40 .

Thank you all for your advices. I hope this may throw some light on the cause.
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Re: Jesan 88-900 erratic output on only 7 high channels

Post by The Collector »

I had a radio that did similar, from 30-40 iirc and it needed a tiny red trimmer adjusting to get it to lock-on properly. I think Nick told me how to do it at the time (probably about 8 years ago now).
original45
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Re: Jesan 88-900 erratic output on only 7 high channels

Post by original45 »

Thanks ,yes Nick suggested in earlier post lock , he would know better than most I'm sure.

I was actually hoping to get it out to try again tomorrow .but what threw me think was when a swr meter was put inline it changes from highs to lows.

I will confirm this again tomorrow and hopefully get some info after updating confirming it's fault so if it does need a trim I'd try that diy maybe.
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