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lbcomms

I know this is a very very VERY old thread but I came across it while trying to figure out what the issue is with my Cobra 29 Classic and Cobra 29LX
Old thread is something of an understatement :lol:

the transmit light comes on and I also get some sort of signal on nearby receivers (several ...

lbcomms

The middle can is usually USB - guess you found one of the not so usual ones :o

Good to see you got it better. Don't go for perfection with this radio, if you get it "spot on" on Mondays it will drift a bit by Tuesday... if you want drift free buy a better radio.

I did not touch the other cans ...

lbcomms

They have the same innards as the Lankar DW-1200, read all about it at http://www.radiomods.co.nz/forum/viewtopic.php?f=5&t=3045 Sorry you'll have to manually copy and paste it into a browser, the board has disabled inserting links into a post...

Frequency adjustment:

http://i60.tinypic.com ...

lbcomms

Current thoughts are towards building an 8 section coax co-linear with a supposed 9DBi gain, taken from a tried and tested 70cm ham antenna design. (obviously re-calculated to 446mhz)
That's only 1.4% above 70cm, a 9dB antenna will have probably 2.5% bandwidth under 1.5:1, so you should be able to ...

lbcomms

How could I test for a bad cap? Would I have to pull to test first? Thanks.

From an electronics and communication engineer with 16 years experience: you don't.

Replacing ALL of them is the only way to make these sets reliable.

If we get in any pre-2000 Uniden chassis for repair, we now insist ...

lbcomms

The most common problem with these 80's / 90's Unidens (except for the golden screwdriver syndrome) is the "10 volt blues".
There will be 15 to 30 light grey 10V electrolytic capacitors, these fail (start to conduct DC, something an electrolytic must not do) after 10 to 20 years.

Replacing ALL of ...

lbcomms

please note that it is not a good idea to re-open posts that are long-dead (more than 2 years in this case) as the original poster is usually long gone.
Hi Warf135, we are still around, though i don't get as much time for forums as I used to. How are things up there in the UK?

Determine a good ...

lbcomms

hot side of the pot has 2.8v but the cold side goes into the rf gain pot
Doesn't matter. Isolate these 2 connections and connect the pot terminals to +V and ground respectively.

delta force magnum has a 5v regulator
No need for that. There is a regulator in the 8 or 9 volt range present in ...

lbcomms

There are many variations on this chassis, so instructions like "cut the pink wire and join the green and brown together" usually won't work, and may even kill your radio!

You need to have some basic idea what you are doing (or take it to someone who does).
Only basic gear needed - soldering iron ...

lbcomms

The mic MUST have the same impedance (resistance) as the radios mic input (600 ohm - 1Kohm)
With RF (sch as the antenna circuit) that's true, but it's a bit different for audio.
With audio, the source (mic) needs to have a much lower impedance than the load (radio).

Most mics are in the 50 to 750 ...

lbcomms

They are almost as bad as a DW-1200!
The Lankar unit was a far worse "radio" - the PC122 might drift a bit, but at least they were reliable.
We had about a 2% to 3% warranty failure rate on the '122, the Lankar units were 80%+. Therefore, going by the warranty returns, the Lankars were 40 times ...

lbcomms

what are the most effective mods for the time/money?
With that radio, not too many. 29's are made to look pretty and be a convenient size for modern SUVs, but as a radio they are fairly mediocre.

Is the 520 or the 2030 going to do better? Or should I stick with the 1969, even? Is the 2sc2312 ...

lbcomms

the am side worked perfectly

That would be like putting skinny bald tires on a Mustang and saying "That's OK, because only use it to drop the kids off to school"

lbcomms

a galaxy A kit will work in them. Also a expo 100 "N" kit will work
Depends on your definition of "work" :)

The '2824 PLL clarifies and does the SSB offsets by varying the 10.240 frequency slightly.
This is halved and then tripled to 15.360 and mixed with the VCO.
The offsets are preserved by ...

lbcomms

point me in the direction of an owners manual maybe
Google the owners manual for "Uniden Grant", "President Grant", or "Cobra 148".
The controls might be in a slightly different place but all of the above are almost identical - the only real difference is the Grant doesn't have the inbuilt SWR ...

lbcomms

Can you mod the tti TCB-880 cb radio from 80 channel too 400 channel

1) Yes you can, any radio can be modded. Some are far easier than others though.

We played around with a very similar one about 3 ago. Got it to do lots of strange things by adding random data to EEPROM IC802 :)
OK so I was ...

lbcomms

That's correct, and why inverted (common to ground) switches are used on most real-world applications.
If you want to play safe, put a low value resistor (say 68 ohms) in the 5V line that feeds both switches, this will limit the current to a safe value (about 75mA) in the event of a short.

Cheers

lbcomms

First of all, make sure they are not inverted - when the switches are at position "0", there should be NO connection between any of the pins (assuming they are 5 pin switches).
If they have more than 5 pins, there should be NO connection between any of the output pins at position "0".

Repeat the ...

lbcomms

where do the resistors and capacitor come into it?
It depends on the switch design - there are 2 types of hex switch.

I only showed the least common type before as it's easier to understand.
These have the common connected to +5V and the outputs are used directly.

There is one problem with that ...

lbcomms

Cheap hex switches in the UK:
http://www.ebay.co.uk/itm/HEX-RED-KNOB-CONTROL-PCB-MOUNT-SWITCH-QTY-1-/110620408748?pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item19c17d7bac

Mount them on some perf board and wire them to the (with the EPROM now removed) EPROMs data connections.
Or, if the ...

lbcomms

The output data in theory could be found by using a truth chart for the MC145106 PLL chip
No, as this can change for different radio designs.

Old school PLLs like the MC145106 were not fast enough to directly control the VCO frequency, so downmixing had to be used so that the thing could work ...

lbcomms

Here's the pinout of the EPROM:
http://i55.tinypic.com/fop3m9.gif

The address lines are the inputs to the EPROM.
The first digit (thousands) is A12. This can only be high (1) or low (0).
The next digit (hundreds) is A8, A9, A10, and A11, so this can be 0 through to F.
The next digit (tens) is A4 ...

lbcomms

Where's the fun in that? :D

sounds like it will be a lots of maths involved

Hex 101:

Numbers in computers (and radios!) are represented by voltages on wires - these can either be off (low) or on (high).
By putting different voltages on different wires, we can "change" things (such as our ...

lbcomms

"4 of the programmable output pins of the eprom are dead"
They are all OK, all 8 lines working are needed to show the numbers you have in the hex dump.

However, it looks like data line D4 (the least sig bit of the tens digit) is in trouble - nearly (but not all) of the combinations are high.
This ...

lbcomms

I have an old major M588 in the shed

There is a PLL02A version of the scanner app - hook that up and you'll have more channels than you would now what to do with

lbcomms

The channel switch codes used for the TC 9??? PLL's are not in any specific order that makes sense, as you can see in the list above, there all over the place.
It's done that way to save cost - the address lines of the PLLs ROM are connected to the LED channel readout pins of the channel switch ...

lbcomms

The eprom reader has 3 wires which goto SDA, SCL and Ground
That's an EEPROM reader, not an EPROM - that extra E at the start indicates a completely different component.

An EEPROM is "serial" - only 2 wires are needed for date transfer (SDA and SCL).
An EPROM is parallel a 64KB device would need ...

lbcomms

Voltages on pins 3 to 10 (the address lines) are needed - you could have a wiring mistake here and be calling up unprogrammed area inside the EPROM.

Does the voltage at pin 6 change between ch. 40 and any other channel? It should stay the same.

Also, I can safely assume you do not have a EPROM ...

lbcomms

Also check the connection to pin 6 of the PLL - it selects the divide ratio (1024 or 2048). I can't see the need for this, as it would have to be set for 2048 to allow the thing to transmit.
((10240 / 2048) * 91) = 455 Khz, which is the TX/RX shift. SSB sets don't need the offset but would need a ...

lbcomms

And so the green wire is still homeless
Cut it off, it must be for another application (radio). If the set receives and transmits OK on channel 1, the 10.240 signal is reaching the 3 places it needs to go.

on any other than channel 1 the power drops right back to barely nothing and the frequency ...

lbcomms

The 10.240 signal is needed in 3 places, so maybe it's an OUTPUT back to the main board.

The signal does 3 things:

1) Reference freq for the PLL (where it's divided by 2048 to produce 5 Khz)

2) Second local oscillator on RX (10.695 - 10.240 = 455KHz)

3) Transmit upmixer (VCO upshifted by 455 Khz ...

lbcomms

it goes to pin 3 of the MC145106 chip
Pin 3 is the input for the 10.240 MHz reference frequency. There is presumably a crystal oscillator on the radio PCB that can supply this signal. The PLL won't work without it...

The '106 is an antique PLL that only goes to 3 or 4 MHz, so there must be ...

lbcomms

OK Gisborne is in NZ
Found it in Wiki. Nice view from the hill overlooing the river / harbour...

and I'm a licenced ham
That'll clear any legality type issues.

The rig has never been abused/modified
Again, that's a good sign. CB experts (the "swing kit" crowd) are your radios worst enemy ...

lbcomms

it is possible to convert this CB to operate in the 10m ham band as an FM rig
Yes, it can be done. The screen capture I showed earlier was where we used one to do a 10 meter conversion - look closely at it...

but at a cost of some $300
That's a rough "guesstimate". You are looking at a 30 year ...

lbcomms

1) Heat up the area around the regulator with a hairdryer

2) TX and adjust for 4W carrier

3) Squirt freezer spray (such as http://www.maplin.co.uk/freezer-spray-26296 ) on components near the regulator, one at a time, until the TX power drops. Leave 15 seconds between each component / squirt.

4 ...

lbcomms

other techs watching
What about engineers?

They don't use ROMs but PLL synthesiser ICs.
They use a mask programmed ROM with a PLL in the same package.

A ROM is a memory device - it has address lines (INPUT) and data lines (OUTPUT).

The address lines connect to the channel switch, TX/RX ...

lbcomms

Toshiba 1SV149 specs
1v: 500pf
500pF is wayyyy to high, the radio will want to go down to about the 40 meter ham band :)
You might be able to "unwind" the coil to make it go back up, but that will cause other problems.
Try to get some suitable varactors first. The BB809 will give you about a 4:1 ...

lbcomms

Unless you recommend removing the second parallel varactor
This won't make any difference to ther range - in an ideal word. In the real world it might help a tiny bit...

First of all, from the datasheet for the BB190:

http://i53.tinypic.com/s4c3l3.jpg

The PLL02A operates over a PD range of 0 ...

lbcomms

before vco quit operating on transmit/receive at 28.705
Like I said before, don't attempt to go that high with the circuit as-is, you'll throw out spurious (unwanted mixing products). Read the earlier post for the explanation.

If you need to go higher (for example, to cover the 10m ham band) you ...

lbcomms

had lack of range/unable to tune,intermittent operation
Two things cause this - bad original varactor (common) or <resistance> leaky 4.7uF electrolytic (rare).

What would be a good pot value? i'm thinking no less than 10k as it will have the 5v feed across it to ground
It's feeding a reverse ...

lbcomms

it did not work to expectation
In what way? lack of range, unable to tune, etc?

Assuming you have a half decent frequency counter and a proper 50 ohm dummy load, the best way to mod / faultfind these is to temporarily disconnect the PLL.
Isolate pins 5 and 6 (make sure they ARE isolated or you ...

lbcomms

This might let you hit 555, but your clarifier range will be lousy and you'll also have problems centring LSB and USB at the same position of the clarifier.

A PLL swap with EPROM addressing (i.e. a MC145106 PLL with a 27C64 EPROM) will solve these issues and give unbroken 5K steps, but like I said ...

lbcomms

It is needed to have coverage from 26.965 to above 28.000 as far as is reliably possible.
What other changes will be required/necessary for the Receiver and Transmitter to broadband the mentioned radio with board PTBMO58COX ?.
They will cover from 26.965 to 28.235 OK. Don't go above this too much ...

lbcomms

You can get 2 to 3 megs out of these fairly easily. Remove it from the radio and remove the epoxy (careful!) on the PIN side. Don't remove the can.

Cut the tracks on the 2 places indicated. Add the 2 capacitors as shown - SMT ones work best, but the really tiny leaded ones will fit if you are ...

lbcomms

Only the control (digital) part of these was out of the ordinary, the RF side was standard NDI 40013 stuff.
There are 2 versions, only the PLL circuitry differed.

Alignment is as for many NDI 40013 radios (single conversion 7.8 Mhz IF with a 19 Mhz PLL on a seperate small board).

Anyone with ...

lbcomms

Yes, but it's not a mod for a newbie. Either buy an easier to mod radio, or take it to someone who knows what they are doing.
It involves rewiring the clarifier and either changing the PLL or changing the downmix tripler into oscillator(s).

Google "upd2824" and you should get all the info you need.

lbcomms

I remember these well - korean made SSB similar inside to several Hatadi units (Super cheeta 3, Super panther 3, etc).
The lankar had an "RF-G" switch that always confused the newbies :)

Only newbies bought these, many radio shops worldn't sell them, they were sold in auto accessory stores and ...

lbcomms

This chassis (along with most other Cobra and Uniden SSB radios) is notorious for bad 10V electrolytics - for the sake of 10 to 20 dollars / pounds, replace ALL 10V caps with 16V ones of the same uF value.
They are getting so bad here we will not guarantee and work on these unless the owners agree ...

lbcomms

What was the purpose of this wire connection originally
It's there to stop illegal frequencies being synthesized if the channel selector is placed "in between" channels.
It disables the transmit mixer (and sometimes the RX, courtesy of some hand soldered components on the print side of the board ...

lbcomms

When channel selector placed between channels TX indicator lights
Is this an 18 channel unit that has been converted to 40?
If so, remove the dark blue wire that goes from near the channel switch to the centre of the board (near the crystal filter, it connects to a diode at this end).
No more TX ...

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