148 Mk2

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satelitesid
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148 Mk2

Post by satelitesid » 16 Aug 2018, 22:22

Wierd one this.
Bloke gave me a 148 to play with, basic line up and add a UK when done.
He reckoned he could hear nobody.
Well he wouldn't a 25 Mhz!
There is problem around 145106, adders are getting correct codes from band switch, and frequency spacing is correct through each band, so channel switch appears ok.
Here's the strange bit.
VCO voltage is correct as per manual, but radio is 680khz low on low and Hi, but 730khz low frequency on mid

Adders seem to be doing what they should, PLL is doing correct spacing and locked.
I must be honest, although I have done dozens over the years, I am a bit rusty, so any ideas accepted.
Also, has anybody tried those chinese 145106 ICs,

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cb4ever104
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Re: 148 Mk2

Post by cb4ever104 » 17 Aug 2018, 01:54

Time to get the service manual out and go through the pll and oscillator section. Have a look at TP3 with the counter and see what's going on. Adders might be ok , but what about the channel selector ? There's a few things that could be wrong , but I'd start with the mk2 manual.

Sammy
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satelitesid
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Re: 148 Mk2

Post by satelitesid » 19 Aug 2018, 11:58

Wrong reference crystal, and wrong core in VCO.

Quite why the hell somebody would change a 15.000 for a 14.31818 is beyond me, unless they couldn't be bothered to find the correct one of course.
Now to try and align it, but being very wary, as I do not know what may have been done previously

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13EL121
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Re: 148 Mk2

Post by 13EL121 » 21 Aug 2018, 18:02

Best way is to swap the xtal to an original UNI 15.000.
I had some tests with other xtals. They dont work well. The coarse Clarifier only slides 2-3kc with non original ones. They are “harder“ to pull on frequency. But they are more stable, so less drift.

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