Nato 2000 No FM/SSB TX. AM okay.
- yaggiboom
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Nato 2000 No FM/SSB TX. AM okay.
Just got hold of a cracking Nato 2000 in near mint condition, I mean its really good, very rare to see one in this cosmetic condition. barely a mark on the facia, all the stickers are there, and I even got an original user manual. The back panel looks almost new still and from what I can tell opening it up today was the first time since the chips were reversed.
But.....really strange goings on, AM is fine, works a treat.
FM and SSB, nothing, no channel display and no TX light.
So, straight to the AVR and there was no regulation. There is two diodes on the AVR, unlike the 133 board, the 10v zener is back to back with looks like a switching diode, checked them and the switching diode was open circuit. I replaced it with a 1N4148 and I get the 10v back on the AVR.
The scope is showing a small output on FM/SSB and having a receiving radio next to the Nato, its audible. RX is perfect, no issues, PLL and VCO circuits all working as they should. I've checked all the other voltages on the relevant locations, Q33, 34, 35 all appear to be working with the correct voltages too. Any Ideas?
But.....really strange goings on, AM is fine, works a treat.
FM and SSB, nothing, no channel display and no TX light.
So, straight to the AVR and there was no regulation. There is two diodes on the AVR, unlike the 133 board, the 10v zener is back to back with looks like a switching diode, checked them and the switching diode was open circuit. I replaced it with a 1N4148 and I get the 10v back on the AVR.
The scope is showing a small output on FM/SSB and having a receiving radio next to the Nato, its audible. RX is perfect, no issues, PLL and VCO circuits all working as they should. I've checked all the other voltages on the relevant locations, Q33, 34, 35 all appear to be working with the correct voltages too. Any Ideas?
- yaggiboom
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- Joined: 22 Feb 2021, 16:24
Re: Nato 2000 No FM/SSB TX. AM okay.
TX light replaced. Normal operation now restored due to a wire badly soldered to the PA switch, so bad that it was social distancing itself from it. So its now rxing and txing on all modes and bands.......apart from band B. That is operating on 27,143 MHz across all 40 channels. Offset is okay, its more fundamental than that, something isn't being switched.
- yaggiboom
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Re: Nato 2000 No FM/SSB TX. AM okay.
So this is where we are for anyone following this. I've traced the issue to the band switch. There are three commons on the PCSW001s LED/binary board. One common is +v volts and that was the cable that was detached from the PA switch, the other two commons are one for band A - D and the other for the FM legal binary input to the loop. These are switched on and off as needed, but I found that band B, the n codes on the loop (pin 2) was 192 on all 40 channels, should have been 255 and descending as with band A,C, and D. Checked the voltage on that common and its +ve except when switching to B, then it disappears. hence the incorrect n code. So, is it the switch that iffy, or another duff wire. We will see tomorrow when I get into the nitty gritty of it.
- Otter
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Re: Nato 2000 No FM/SSB TX. AM okay.
Ah, the band switch uses a different wafer for UK, so it's probably a wire off or the switch again.
"To this day the words Stirling bridge conjour pride in every Scotsman's heart, while to an Englishman those same words conjour literally no feelings at all." - Cunk on Britain S1 E1
- yaggiboom
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Re: Nato 2000 No FM/SSB TX. AM okay.
Its the band switch that is causing the issue. The channel wafer switch is all good but the band switch operates like a revolving DPDT in that power to the ABCD is on until it reaches the FM band and it switches off one common and switches on the other. At the same time its switching power to the individual crystals too. I am about to take the radio apart to get to the wiring on the switch, wish me luck
- yaggiboom
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Re: Nato 2000 No FM/SSB TX. AM okay.
The offending switch with a common wire that is soldered along four contacts. So I have replaced it with a much better piece of wire and soldered it in nicely. Some of the soldering done at the factory is frankly, shoddy work. But my effort has paid off, after all the faults this radio had to begin with, TX lamp, 9v zener and shunt diodes, connection on the CB/PA switch and the band switch, its no wonder this radio has shown little use, it barely worked at all. Now its perfect, all is working great, and I have myself a little bargain.
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- yaggiboom
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Re: Nato 2000 No FM/SSB TX. AM okay.
Here is the radio, great condition, working a treat.
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- yaggiboom
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Re: Nato 2000 No FM/SSB TX. AM okay.
I decided to make a significant improvement on the problem Q36 (2SD837) has with dissipating heat. I noticed on the Alan 88s that it was on the main heatsink. So I took off the heatsink and added holes and threaded one for the mod. Also to really make it worthwhile the original place where it sits on the board is connected with wirewrap termination. It looks good, and works well.
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Re: Nato 2000 No FM/SSB TX. AM okay.
Brilliant bit of fault finding and nice work, radio looks really nice. A mate if mine had a Nato 2000 back in the 80’s, very distinctive sound switching from USB to LSB i seem to recall.
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Re: Nato 2000 No FM/SSB TX. AM okay.
Really well done, I'm scratching my head around a not to dissimilar problem.
You have provided me with some good old detective work, so I can now progress my NATO 2000.
You have provided me with some good old detective work, so I can now progress my NATO 2000.
- yaggiboom
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- Joined: 22 Feb 2021, 16:24
Re: Nato 2000 No FM/SSB TX. AM okay.
There are weak points in these radio's and it appears they suffer more faults than the standard cybernet alternative 131 board. One of the weaknesses is the clipper diode that is part of the Q36 regulator circuit. On the 131 board the clipper diode isn't used. When it conducts the zener voltage increases +0.7v and if the voltage rises above this it clamps the voltage to reduce it. An open circuit here will stop the zener regulating altogether.