Cobra 148 MK2 10Khz off All Bands

A forum for the discussion of matters of a technical nature. All such activities are undertaken at the readers discretion and own risk. If you don't know what you are doing, don't blame us if it all goes wrong!
currentstatus
Regular
Regular
Posts: 45
Joined: 18 May 2018, 06:50
Location: Valencia, Spain

Cobra 148 MK2 10Khz off All Bands

Post by currentstatus » 23 May 2018, 18:43

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?

IMG_5775.JPG
IMG_5776.JPG
You do not have the required permissions to view the files attached to this post.

User avatar
ROTEL240
Super Member
Super Member
Posts: 384
Joined: 01 Dec 2012, 20:10

Re: Cobra 148 MK2 10Khz off All Bands

Post by ROTEL240 » 23 May 2018, 19:35

Black spirit is you man to solve your problem

User avatar
radiogaga
Top Poster
Top Poster
Posts: 1472
Joined: 04 Sep 2010, 20:37
Call Sign: 26TM399

Re: Cobra 148 MK2 10Khz off All Bands

Post by radiogaga » 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 !
26TM399 Hampshire and Isle of Wight
30TM399 Northern Costa Blanca

User avatar
cb4ever104
Veteran
Veteran
Posts: 4544
Joined: 28 Jul 2011, 21:26
Location: Alicante , España

Re: Cobra 148 MK2 10Khz off All Bands

Post by cb4ever104 » 23 May 2018, 20:13

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

Samny
30TM060
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.

currentstatus
Regular
Regular
Posts: 45
Joined: 18 May 2018, 06:50
Location: Valencia, Spain

Re: Cobra 148 MK2 10Khz off All Bands

Post by currentstatus » 23 May 2018, 20:46

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.

currentstatus
Regular
Regular
Posts: 45
Joined: 18 May 2018, 06:50
Location: Valencia, Spain

Re: Cobra 148 MK2 10Khz off All Bands

Post by currentstatus » 23 May 2018, 20:46

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!

zephyr
Radio Addict
Radio Addict
Posts: 741
Joined: 01 Nov 2007, 15:31

Re: Cobra 148 MK2 10Khz off All Bands

Post by zephyr » 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.

User avatar
slamjam
Radio Addict
Radio Addict
Posts: 672
Joined: 02 Nov 2010, 18:52
Call Sign: 26DT871
Location: Suffolk JO02

Re: Cobra 148 MK2 10Khz off All Bands

Post by slamjam » 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?
IC-756PRO - IC-756PRO 3 - FT-1000D Classic - FT-990 - Acom 1000 - TS-2000 - TS-790e 2/70/23cm- TS-850SAT + XV144 -Superstar 360FM - Galaxy Saturn 2 - Icom ICR1000

currentstatus
Regular
Regular
Posts: 45
Joined: 18 May 2018, 06:50
Location: Valencia, Spain

Re: Cobra 148 MK2 10Khz off All Bands

Post by currentstatus » 24 May 2018, 12:47

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?

currentstatus
Regular
Regular
Posts: 45
Joined: 18 May 2018, 06:50
Location: Valencia, Spain

Re: Cobra 148 MK2 10Khz off All Bands

Post by currentstatus » 24 May 2018, 12:48

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".

User avatar
cb4ever104
Veteran
Veteran
Posts: 4544
Joined: 28 Jul 2011, 21:26
Location: Alicante , España

Re: Cobra 148 MK2 10Khz off All Bands

Post by cb4ever104 » 24 May 2018, 13:35

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

Sammy
30TM060
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.

currentstatus
Regular
Regular
Posts: 45
Joined: 18 May 2018, 06:50
Location: Valencia, Spain

Re: Cobra 148 MK2 10Khz off All Bands

Post by currentstatus » 24 May 2018, 15:30

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..

User avatar
cb4ever104
Veteran
Veteran
Posts: 4544
Joined: 28 Jul 2011, 21:26
Location: Alicante , España

Re: Cobra 148 MK2 10Khz off All Bands

Post by cb4ever104 » 24 May 2018, 18:28

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, 18:43
Also 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.
30TM060
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.

zephyr
Radio Addict
Radio Addict
Posts: 741
Joined: 01 Nov 2007, 15:31

Re: Cobra 148 MK2 10Khz off All Bands

Post by zephyr » 24 May 2018, 20:27

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.

User avatar
cb4ever104
Veteran
Veteran
Posts: 4544
Joined: 28 Jul 2011, 21:26
Location: Alicante , España

Re: Cobra 148 MK2 10Khz off All Bands

Post by cb4ever104 » 25 May 2018, 07:25

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

Sammy
30TM060
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.

Post Reply

Who is online

Users browsing this forum: No registered users and 5 guests