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

zodiac

This may be a bit too late but IC6 the audio chip and TR39 do get hot.
What voltages are you getting on IC4 in TX and RX.

zodiac

It sounds like the big regulator transistor bolted to the side of the chassis at the back right hand side has gone.
That's why you have no control of the FM power and no AM audio.

zodiac

If the Final has gone short circuit it will take the receive out as well in most cases.
Check to see what current is being drawn by the radio in RX, it should be next to nothing.
If it's more than about 1/4 of an Amp de-solder the final and see if the receive comes back to normal.

zodiac

Just put the Yellow wire from the SFT position on the board that was removed from the band switch, to the N position just above R174 where the Black wire is now, remove the Black wire that's at 0v. You will also have to extend the VCO to cover S.Low to S. High, if you haven't already done it. Dave, ...

zodiac

This should help you out with the wires and switches.

MK2 wires.png: (297.03 KiB) Downloaded 124 times

zodiac

Hi Pete,
If you haven't sorted it yet all you need to do is change the 14.550Mhz crystal to a 15.900MHz.
By doing so you will move the radio up in frequency by three bands to 29.655MHz channel 40 the highest band.

zodiac

Hi Jason and welcome to the forum.
That's a strange one you've got there, try de-soldering the finals to see if the amps drop and tell us what the finals are, Mosfets or 1969's.
If you have a shorted final it will kill the receive.

zodiac

Charlie,
All I can tell you is, if the PA is working then the audio chip is good and not the fault.

zodiac

Edward, I know what you mean about falling asleep. Lou Franklin does his best to explain in simple terms most of what you need to know for the beginner in his book, THE SCREWDRIVER'S EXPERT'S GUIDE. If you need a book to get started with that won't put you to sleep, there was a book from Radio Shack...

zodiac

Just fit it Jon, it'll work fine.
You could tune the crystal for high band to get down to the UK band but you won't get all the channels.
Channel 33 will be 19 UK up to 40 for channel 26 UK.
Dave.

zodiac

I now use PIC's instead of an Eprom for that mod, it only needs a 2 pole switch instead of 4 poles with the Eprom. I've got two Jumbos I'm doing at present with MK2 Cobra 148GTL DX radios being fitted with the 3900 counters and zero switching using a PIC. Did one the same last year with a 3900 in an...

zodiac

Do you want to lend one of my hammers

zodiac

Animal,
You forgot to mention the two varactor diodes D40 and D44 that need changing to ITT410 or same as.
You may find that a 4.7uh coil will do the same job as a 5.6uh.

zodiac

Forget the standard mike, use the lollipop.

zodiac

Well we learn something new every day, and you've explained it so well.
Thank you.

zodiac

The 777 doesn't have a beep fitted as standard like the Nato, you'll have to fit one.

zodiac

3900's with plugs and socket at the front of the radio are all marked, +8v, RB (roger beep), +10k etc. where all the pins connect to on the board right at the side of the sockets. So if your radio has not been wired for the function you required just look at a schematic for the 3900 that has those f...

zodiac

As I said the orange wire on the left is for switching the beep on and off. If you hard wire the channel 9 switch for 1 to 40 you can then use that switch for switching the beep or for the +10kc, the +10kc when wired to a switch will take you up by one channel making it possible to get to the five a...

zodiac

I think the orange cut wire on the left is the beep wire, just put it to a switch so you can switch it on or off. The other wire at the channel switch is like that in all the 3900's, that's normal. Yes they are trim pots (adjustable VR's) but leave them alone till you've got it going then see if the...

zodiac

It looks like it's one of the later radios but before the crap Ranger ones, because it's got the frequency counter socket on the back of the radio for a counter. Does the SWR/CAL switch pull out to open the radio up to all bands and with it in you only get Mid band 26.965 to 27.405. The ALC looks to...

zodiac

Alex, It's no good banging your head on the wall, you should be hitting the radio with a bigger hammer LOL. You say it only lasts about 30 seconds before it blows again but in what mode are you testing it in. I would have thought with only 10mA at the driver it shouldn't have done any damage at all....

zodiac

It sounds like there is a short from the collector to the chassis of the 2166.
Make sure there is no connection between the two, do a continuity test from the tab of the driver to the chassis just to eliminate that possibility.

zodiac

Alex,
You only check the voltage at the base of the driver and the final one then the other, with the black probe of your meter to the PSU's negative connection.
With a dead key in side band mode there should be no more than 0.7v.

zodiac

I would set them both at 50mA, then check to make sure there is no more than 0.7v at the base pin of both, as I said above.
Dave.

zodiac

Alex, Your not using a 477, you have a 1969 in there, If you adjust the bias to 80mA it will probably overdrive the final (1969) you are using, there should be no more than 0.7v at the base of the final and driver, with a dead key on side band and the mic gain set at zero. If you think the capacitor...

zodiac

The 1969 has a different pin out to the 477 and you must cross the emitter and collector over to get it to work. If you use a 2SC1945 as a replacement for the 477 they will fit without having to change the pins over but you will only get about 10w from it. The bias for the 2166 should be 50ma and th...

zodiac

It should be a case of replacing the correct transistor MRF477 for the 2SC1969 and checking the bias but make sure that the two capacitors C187 and C188 (both 560pF) have not been removed, if they have then you must replace them.

zodiac

Norm,
You could have sent it to me and I would have programmed you another one, as long as the original program is stil on it.
Dave.

zodiac

Norm, Don't bother looking for a truth chart for any other radio that uses the 145106 PLL, it won't help you, It'll just make matters worse. 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....

zodiac

Yes Norm, High is / and blank is low. Don't forget they are different boards, mine is the ISS3 and uses a 2732 EPROM not the 2764, having said that the switch codes to the EPROM input pins should be the same, they can't change. I can offer to read your EPROM for you so you'll have the program that's...

zodiac

Don't know if this is of any use to you Norm, this is for the ISS3 LC1 board

: 160 Codes.gif (14.33 KiB) Viewed 66678 times

Dave.

zodiac

If you need the schematic for that radio you'll find it on CBTricks.com
under radio information, then "A" for Amstrad 900/901.

zodiac

The board number is at the back of the board on the Cybernet 134 radios that use the LC7137 PLL but other radios also use the same PLL.

zodiac

I can't remember what board is in that radio but if it's the 134 board with the LC7137 UK PLL in it, don't bother.
The only thing you can do is add the LC7132 FCC Mid band PLL to give you 26.965 to 27.405 but it's not that simple.
Both PLL's are ROM chips and cannot be altered.

zodiac

Have you tried making the adjustment when the radio has warned up first, or did you do it while the radio was cold.

zodiac

Max,
You can adjust VR1 for AM/FM receive and VR2 for SSB.
Dave.

zodiac

The Tip146 is a darlington PNP transistor, you could use a TIP2955 PNP 15A transistor at about 80p each depending on where you buy it from. I don't think you are looking in the right place for the fault. Before I go any further, what are the output transistors that are fitted in the radio or are the...

zodiac

I've never see the radio so I cannot say much about it but it's two channels missing between the bands A and B. That might be a clue as to make me think it's been extended as you say and if so, it hasn't been re aligned to ensure it has stability. I supose the answer is not to use it on those two ba...

zodiac

Your in the right place, Scott's the man to see for the conversion.

zodiac

Take a look on transmission1 in the Uk at Clint's post, "converting my AR144 to 555"
http://www.transmission1.co.uk/forum/vi ... 35&t=16811
They are the same board and the information is very good with phots.

zodiac

Check or replace C167, 10v @ 330uf for a 16v @ 330uf, do the same with C172, 10v @ 47uf for 16v @ 47uf.

zodiac

Your welcome and if you ever need a S.Hi crystal I've got loads of them.
Dave.

zodiac

I've posted you one of each, with a bit of luck that should sort your problem out.

zodiac

What type is it, is it plug in or soldered in.
Dave.

zodiac

How many do you need.

zodiac

You've got a slightly different board than what I'm looking at, yours has a capacitor on the side shown and no resistor. The board I'm looking at is the 119AA, the first board used in the radio. If you do take the board out it might be worth changing the IC for what it would cost, you never know it ...

zodiac

This is the FM board, I've cleaed it up a bit but you can now see the resistor.
Maybe the newer radios have it mounted on the other side of the board as the diagram is for the PB119AA board.
Dave.

zodiac

Board PB119 is the FM board and the FT402 is the .455 filter and FT401 if the 10.7 filter or it may have a crystal filter 10.695. I have seen the crystal filter with a broken lead before today so make sure that's not your problem. The 10ohm resistor is to the right of the .455 (FT402) filter and the...

zodiac

It sounds like the Mid band crystal has had it's day and needs replacing, what frequency is on it as I might have one.

zodiac

What hakkeri2 is saying is, that on the FM board you can see only one resistor on the component side of the FM board with the IC and the two filters, that is the 10ohm rasistor he's talking about. On the other side of the board is an electrolytic capacitor that can cause the resistor to go faulty, i...

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