The Defpom Forum, for RadioMods, S&M Software and Music by The Defpom

howdy all,
here we have a cobra 148gtl dx missing 6 channels from 28245 to 28305
super hi channel 35 to 40 .
its ok to channell 34 ,28245 then from 35 to 40 frequency stays at 28245.
the rig has a 6 position band switch fitted, and a uk40 eprom that is on position 6,position 5 is super hi,

thanx guys for any help

What markings are on the EPROM, I am just wondering if it is one of my units, as I did a 148 with a 6 band switch and UK EPROM many yeras ago in the UK.

It could be an EPROM issue, (miss-programmed or failing) if they are the very top channels, then it could just be that the VCO is out of alignment and needs a tweak.

Do let me know if the EPROM has a label on it, and what s marked on it.

hi scott,
sorry for taking long time to reply had some family buissniss,
the only markings i can make out on a dirty white sticker on the eeprom is OB2??,

Thanks for the reply, it does not sound like one of mine, they had silver stickers.

scott is it possible to desolder the eprom and reprogram it,i think i have a programmer some where,

thanx angus

You can drop in another EPROM which has been programmed for the radio, as long as all of the band switch options have also been programmed into it, the raw data stored on the device is not "read" in the normal way, so you cant just go into it and see what it is doing, you have ton understand the binary codes that are present and wanted on the devices inputs and outputs for every single channel and band...

I would definitely not erase the EPROM you have, get a blank one if you are going to experiment, and solder in an IC socket so you can just plug in the EPROM, you wont risk damaging it from heat from soldering that way.

hi scott thanx for helping,
well to be honest this is another radio, ham international multimode 2,
pll02a,with spectrum eprom fitted giving normal low/mid/and high,
then with eprom ading uk 40 and an extra low band,it was working fine till i moved it to another room,then the channels went tits up ,now it only works on the extra low band and the next band up witch would be its standard low band,and only some channels on the next band up witch would be its normal mid band,so it has lost its standard high band and the eprom uk 40 band,
so i deciced to take a look with the cases off 1st thing i noticed was the eprom was very loose moving around the holding screw had come loose where it gets it ground earth to make it work,so looks like its been getting bad contact like switching it on and off rapidly with the loose earth,
then had a good look around and noticed that the pllo2a chip has a little hole at the top near pin 8 not sure if its a defect or a blow off piece,also got the volt metre out and checked the pins +5 and 0v for bincode and on channel 40 it adds to 287 and channel 1 adds to 331,

hope you can help scott .
thanx angus

A hole in the PLL is probably not a good sign...

My suggestion it to set the radio on CH1 on EACH band and get the N codes, post them here, that will tell me if the EPROM is the problem or the PLL, as if the N code are shifting by the correct amount for each band, then it should indicate if the EPROM seems to be OK, or if the PLL is failing to generate the correct chanels.

hiya scott,
testing with uk40 switch off so rig should work as standard on low mid high bands,.

readings for channel switch pin side to eprom are as follows
low band channel 1=319
mid band channel 1=319
high band channel 1=319

that is
15=+5
14=+5
13=+5
12=+5
11=+5
10=+5
09=0v
08=0v
07=+5

readings for pll02a pin side from eprom are as follows
low band channel 1=300
mid band channel 1=300
high band channel 1=300

15=0v
14=0v
13=3.9v
12=3.9v
11=0v
10=3.9v
09=0v
08=0v
07=5v
also turning the eeprom uk40 switch on it stays the same

angusuk,
The channel switch side of the Eprom will always have the same codes going into the Eprom, they never change with the bands.
Check to see if the 5v that run the Eprom are there, it's a common fault with the spectrum Eproms to brake the pins off the 7805 5v regulator and if that's happend you'll have no 5v to run the eprom with.
The Eprom for the O2A PLL will not work in a uniden radio without being re programmed after wiping it clean.
As Scott says try the VCO in the Cobra it sounds like it just needs a very slight adjustment

Dave.

im pritty sure the eprom has gone titsup,
i checked the volts on pins 15 to 7 from the eprom to the pll02a one at a time while turning the eprom uk switch on and off and it dident make any change,shouldent the eprom send a differant n code when the uk40 is
switched in.

Yes it should.
Angus to help us help you can you tell us what the number is on the Eprom.
2716/32/64/128/256 or it may have a C in the number like this 27C16.
Dave.

hi dave thanx for helping,
the eprom is a 2732 ,
the board i a PTBM059COX

also the 7805 is ok i allready tried another one
and the 5volts to pin 24 is fine

angus,
Remove the PLL then check the binery codes again, if they are correct replace the PLL with a good one.

Dave.

hi dave,but if thers no change in ncode to pllo2a when switching uk in from the eprom doesent that point to broke eprom,

Yes that's correct but with the PLL removed theres nothing to pull the codes to ground if the PLL is at fault in any way, as you did say the PLL had a hole in it.
Give it a try and let us know the results.

dave scott,
i removed the uk eprom board and reconnected the pll02a as it should be
now it wont work on any channel, i checked the ncode to the pll02a from the channel selector and it is 255 on channel 1 as it should be,
so i guess the eprom is ok???
any ideas ,wished i had a spare pll02a

also i wonder if its dun the eprom and pll02a

also i have had agood look at the pinhole i thought was a blow hole
with a good magnifier glass and i think its just the mark showing pin 1,

hi all,
the problem was the eprom and the pll02a was blown ,replaced both and
the radio is now working fine again.

cheers angus