Cobra 148 MK2 10Khz off All Bands

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currentstatus
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Cobra 148 MK2 10Khz off All Bands

Post by currentstatus »

This one has me going around & around the room!

Cobra 148 MK2 PB-010AB

It had an eprom which I removed "see pic". I’ve restored everything back to standard.. rotary 3 way.. A1012 "was TIP2995".. and tr50 was a TIP43c ? wire colors restored and cleaned up. Also re-aligned the PLL TP-3 16.49000 mid / TP-2 5.4v and partly the TX. But the whole radio is exactly 10Khz out "ch19 is 18" etc.. low/mid & high.. TX/RX.

I’ve tested the majority of PLL diodes which are fine.. the adders are showing correct voltages but.. the PLL does have incorrect voltages on pin 10, 11, 17 & 18 .. they are driven by pins 13 & 12 of IC6 and pin 10 of IC7 respectively (pin 18 of PLL being ground).

What am I missing.. any ideas?

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ROTEL240
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Re: Cobra 148 MK2 10Khz off All Bands

Post by ROTEL240 »

Black spirit is you man to solve your problem
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Re: Cobra 148 MK2 10Khz off All Bands

Post by radiogaga »

Maybe you have checked but are you sure that the previous owner hasn't added a 10Khz shift?

I'm in a dash but this is the instructions of how it's achieved, make sure someone hasn't done it and it's somehow been made permanent.

All that you need to do is remove JP54 and put a 4.7 K Ohm resistor in its place (located by IC6), then connect a wire onto pin 9 on IC6, run this wire to a switch and connect the switch to a 8 Volt supply, when the switch is turned on the set will go up one channel !
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Re: Cobra 148 MK2 10Khz off All Bands

Post by cb4ever104 »

I had the same fault a few years back . Binary adder was faulty. Check your N codes.

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Re: Cobra 148 MK2 10Khz off All Bands

Post by currentstatus »

radiogaga wrote: 23 May 2018, 19:48 Maybe you have checked but are you sure that the previous owner hasn't added a 10Khz shift?

I'm in a dash but this is the instructions of how it's achieved, make sure someone hasn't done it and it's somehow been made permanent.

All that you need to do is remove JP54 and put a 4.7 K Ohm resistor in its place (located by IC6), then connect a wire onto pin 9 on IC6, run this wire to a switch and connect the switch to a 8 Volt supply, when the switch is turned on the set will go up one channel !
Thanks for that.. JP54 is intact and there are no resistors. Pin 9 of IC6 is 0v as expected.
One thing I noticed.. ch3 is 26.995.. ch7 is 27.045.. ch11 is 27.095 etc.. so these are all the in between frequencies?
Channel structure is not defined.
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Re: Cobra 148 MK2 10Khz off All Bands

Post by currentstatus »

cb4ever104 wrote: 23 May 2018, 20:13 I had the same fault a few years back . Binary adder was faulty. Check your N codes.

Samny
May need a brake.. I'll delve into it more later.. cheers!
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Re: Cobra 148 MK2 10Khz off All Bands

Post by zephyr »

It is possible to adjust the coils too far and put the radio onto the next channel, see if you can adjust the FM coil on channel 19 mid band for 16.490
without much effort.
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Re: Cobra 148 MK2 10Khz off All Bands

Post by slamjam »

Has it got the original Uniden spec crystal in it? If someone has swapped it for a normal 15mhz one this could be part of the problem?
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Re: Cobra 148 MK2 10Khz off All Bands

Post by currentstatus »

zephyr wrote: 23 May 2018, 22:19 It is possible to adjust the coils too far and put the radio onto the next channel, see if you can adjust the FM coil on channel 19 mid band for 16.490
without much effort.
Tried that just now.. the only way to lock ch19 @ 16.490 is when L18 is around 7.9v (should be 5.4v). And also the TX carrier sounds like it's struggling a bit.

JP54 & JP55 are intact so it rules out that 10Kc mod.
Does anybody recognize that EPROM in the pics.. I'm wondering if any on-board component(s) have been swapped out to accommodate it?
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Re: Cobra 148 MK2 10Khz off All Bands

Post by currentstatus »

slamjam wrote: 24 May 2018, 12:04 Has it got the original Uniden spec crystal in it? If someone has swapped it for a normal 15mhz one this could be part of the problem?
Yep they all look original.. most are marked "UNI".
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Re: Cobra 148 MK2 10Khz off All Bands

Post by cb4ever104 »

Just want to check . Is every single channel off by -10khz . Have you checked them all ?

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Re: Cobra 148 MK2 10Khz off All Bands

Post by currentstatus »

cb4ever104 wrote: 24 May 2018, 13:35 Just want to check . Is every single channel off by -10khz . Have you checked them all ?

Sammy
Hi Sammy

Low Band
ch1 - 26.525
ch2 - 26.535
ch3 - 26.545
ch4 - 26.565*
ch5 - 26.575
ch6 - 26.585
ch7 - 26.595
ch8 - 26.615*
ch9 - 26.625
etc..

It's pretty much the same scenario for mid & high band. So yes it's exactly 10Khz above every channel including the alphas.

On further testing Low and Mid.. the adders "both" are showing incorrect voltages. So the chips are probably working but maybe a duff component somewhere.. diode, resistor.. shall carry on testing..
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Re: Cobra 148 MK2 10Khz off All Bands

Post by cb4ever104 »

If all channels are off , then it's not the ch. selector . Nor is it the adders. Measure the crystal frequency . What value do you get ?

Edit: Scrub that . I just re-read your original post .
currentstatus wrote: 23 May 2018, 18:43Also re-aligned the PLL TP-3 16.49000 mid
Maybe the 10.965 stage ? Check TP6 .
Last edited by cb4ever104 on 25 May 2018, 07:49, edited 1 time in total.
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Re: Cobra 148 MK2 10Khz off All Bands

Post by zephyr »

That Eprom could be a copy of the Spectrum Eprom that most people copied as they didn't have the knowledge to program their own.
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Re: Cobra 148 MK2 10Khz off All Bands

Post by cb4ever104 »

Also . What frequency are you getting from the 10.695 stage at TP6 ?

Sammy
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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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