148 GTL DX Mk1 - eeprom and crystal questions

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486dx4
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148 GTL DX Mk1 - eeprom and crystal questions

Post by 486dx4 » 29 Nov 2019, 16:59

Hi All - I have a Cobra 148 GTL DX Mk1 (PC-879 board) which has an eeprom mod that has expanded the radio's frequency range from 26 MHz to 28 from the stock 26.515 to 27.855 which makes it work like a Jackson or the Superstar 3900 with their number of bands. The radio is working but needs its on/off/squelch pot and dual clarifier pot replaced. The radio is missing its x4 crystal and all of its related components (LB 209 IF cans, diodes, inductors, etc). The X3 crystal is 15.480 Mhz and the X2 crystal is 14.595 Mhz. And the band switch is replaced with a 5 position unit to get the 5 bands versus the 3 position the stock radio had. The radio still has its MB8719 PLL chip. Does anyone happen to have documentation on how this eeprom was wired up to the radio?

I was thinking of putting the radio back to the way it was which I know of course is a project and does cost. I have a junk board that I can put back the components on the X4 section and the three position switch. What I would need are the two proper crystals for the bands other than the 15.480 Mhz crystal which is there. The block diagram for the Mk1 I found has x2 at 15.48 MHz, X3 at 15.93 MHz, and X4 at 16.38 Mhz. While the schematic I found and info on another site has X2 at 15.03 MHz, X3 at 15.48 Mhz, and X4 at 15.93 Mhz. I would say the schematic and info from that site is the correct one but I am not sure. Has anyone had these crystals made at Quartslab in the UK by chance? Are there any special parameters you need to give them if you did happen to order these crystals from them?

Any info on the modification and/or crystals would be great - thanks.

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Re: 148 GTL DX Mk1 - eeprom and crystal questions

Post by Edd200sx » 29 Nov 2019, 17:41

I think the problem getting them cut is they usually lack slide.
Also I’m pretty sure 15.03 etc are the ones you want

I’d ask nick for confirmation

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Re: 148 GTL DX Mk1 - eeprom and crystal questions

Post by Otter » 30 Nov 2019, 09:48

Edd200sx wrote:
29 Nov 2019, 17:41
I think the problem getting them cut is they usually lack slide.
Also I’m pretty sure 15.03 etc are the ones you want

I’d ask nick for confirmation
The Nick referred to here is Black Spirit.

There is a place in the Czech Republic that will cut crystals to the same specifications as a sample that you send them. Just make sure you tell Josef exactly what you want. You'll have to send a sample though.

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Re: 148 GTL DX Mk1 - eeprom and crystal questions

Post by cb4ever104 » 30 Nov 2019, 10:14

486dx4 wrote:
29 Nov 2019, 16:59
The block diagram for the Mk1 I found has x2 at 15.48 MHz, X3 at 15.93 MHz, and X4 at 16.38 Mhz. While the schematic I found and info on another site has X2 at 15.03 MHz, X3 at 15.48 Mhz, and X4 at 15.93 Mhz. I would say the schematic and info from that site is the correct one but I am not sure. Has anyone had these crystals made at Quartslab in the UK by chance? Are there any special parameters you need to give them if you did happen to order these crystals from them?
The 15.030 gives you 26.515 to 26.955
The 15.480 gives you 26.965 to 27.405
The 15.930 gives you 27.415 to 27.855

A 16.380 will give you 27.865 to 28.305 .

I have an early mk1 which has factory 15.480 , 15.930 and 10m xtal fitted . Think it's a 16.520 or 530 . Can't remember now . Otter's link looks like a good place to get them as you won't get the same slide on non UNI crystals .

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486dx4
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Re: 148 GTL DX Mk1 - eeprom and crystal questions

Post by 486dx4 » 02 Dec 2019, 13:05

Ok - I had no idea about certain crystals not giving enough slide. I was more concerned about parameters like load capacitance, etc which may have something to do with this - I am not too knowledgeable about crystals. I was looking at that Czech link before posting. Thanks for the info everyone on this.

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Re: 148 GTL DX Mk1 - eeprom and crystal questions

Post by cb4ever104 » 02 Dec 2019, 13:12

486dx4 wrote:
02 Dec 2019, 13:05
Ok - I had no idea about certain crystals not giving enough slide.
If you need a certain crystal then your best bet would be to ask on here (Wanted section) , or on any other CB forum first , as someone may have an old one kicking about .
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Paul aka "Sammy". (108) PY60 Old Paisley DX Group (RIP Rab Markie)
Ex GM0 , now EA5 .
Handle "Fortune Hunter" back in "the day"
Radios ....? Anything that says "TAIWAN R.O.C" on the back.

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