Marconi 2018
Posted: Fri Jul 17, 2026 6:55 pm
I bought two Marconi 2018s at the Newbury rally, both not working and a few keys missing from the keyboard - though not the same keys.
One was £45 sold as "stopped working during storage" and the other was £20 and sold as incomplete.
The incomplete 2018 was missing its Frequency Standard board, but the oscillator was still present. The standard board divides the oscillator by 10,000 to provide a 1kHz reference to the synthesizer and handles the switchover to external clock source, too.
My first job was to see how badly messed up this incomplete unit was, by substituting the Frequency Standard board from the supposedly working one. This didn't make it spring into life. The computer did not appear to be communicating with the other boards, but was running and starting up.
Instead of swapping the board back I decided to board swap it until it worked but first I'd check the capacitors in the PSU.
Sure enough all the small Philips blue capacitors (22µF and 4.7µF) were well down in value (3µF and 1µF respectively), so I changed them. I also took out the chunky 15mF 16V smoothing capacitor for the +5V rail and somehow managed to misread it as 18.5µF, so I changed it. Later I put my glasses on and discovered that it was actually 18.5mF, I'd forgotten that the small tester I was using switches to milliFarads. I had tested the small capacitor on my Wayne Kerr B605 so I'm not sure why I didn't test the big one on that, too, but it was hot and I was tired and my vision was blurry.
I decided that as the computer comms problem was preventing anything from happening and limiting my diagnostic options I'd switch back to the other supposedly nearly working unit. This turned out to be not really the case, in many ways, but the computer *was* working and so was the front panel and something was appearing on the display. The output, though, was nothing because the reverse power protection was triggering once the computer finished booting. Removing the connector that contained the input to the RPP measurement diodes allowed it to boot but it was clear that the display wasn't right.
I decided to use the rebuilt-PSU generator as the project and the "working" 2018 as the donor, the deciding factor being the "working" PSU which had been modified for no obvious reason so the +5V adjustment range started at 5.25V and went up to around 7V, which I thought may have damaged some TTL or one of the divider ICs. This turned out not to be a particular problem but a duff keyswitch sealed the fate of the front panel and later I discovered that the frequency display had some bad segments (could be the decoder/driver chip).
With the Frequency Standard board now moved back to the more broken of the two I found that it would occasionally boot. Changing the CPU and reseating the EPROMs seemed to make it better but it always started up with an error indicating a bad checksum in the EAROM.
I also had no synthesizer lock, but it was switching between oscillators. There was no output on the front panel, though, only at the intermediate point where the RF comes from the synthesizer into the AM/filter/amplifier box. I took the easy way out at this point and substituted two divider boards in the synthesizer which brought back the fine steps but only above 32.5MHz. This meant that the BFO circuit was not doing its thing, so I changed that and got 80kHz to 32.5MHz back. The attenuator on this one seemed to be fine, though the output levels were all wrong, it was at least going through 10dB steps as it should.
Then I tried FM, but there was no FM at all. It seems that with an empty or corrupt FM calibration table the generator can't do FM. Additionally there seemed to be a problem with the FM/modulation oscillator board, so I swapped that over, too. After a very long calibration process with my trusty (slightly broken) 2305 I had working FM.
Now it was time to look at the output level, which seemed not awful on the BFO output but very poor at the UHF end, even with the calibration cranked up all the way. The output amplifier board had been modified due to excessive gain. Rather than back the mod out I just changed it and this brought back full level adjustment and amplitude calibration was a success with plenty of gain in hand. I didn't realise before, but these generators can easily do +20dBm with a bit of deliberate mis-calibration. AM calibration also worked but I wasn't able to stop it being a few percent over at UHF, so I may revisit that soon.
The front panel needed attention so I put together the best switch caps from both to give it a full set. Two LEDs were also not working, the AM indicator and the 6kHz modulation oscillator indicator. I changed both multiple times, turns out the + symbol on the silkscreen is on the cathode. No idea why but not the first time I've seen this on test equipment. I didn't have any 2mm LEDs for the 6kHz indicator or proper yellow 3mm for the AM switch, but I managed to pull the 2mm LED from the other front panel and have used a sort of orangey LED instead of yellow for the AM switch. It's actually the same colour as the switch, which almost made me change all of them…
I'm now trying to get the donor unit working to some extent, as I am sure I can bodge a Frequency Standard board quite easily and I'd like to get board level fixes done where possible.
I had originally intended to sell the 2018 at McMichael but it wasn't ready in time - just the LEDs, really, but I'd worn myself out and had little sleep, hadn't managed to get to to the storage unit to grab some other items I wanted to sell. I may make it to MK to sell, though. I'm definitely keen on getting rid of my 853/8558 (with bonus broken 8559 and incomplete 8557 in flatpack form), possibly my 3325B, because it's a hateful thing that breaks whenever I need it, some Fluke 8502 ac meters, maybe my RACAL 1992 and 9300B and a few boxes of components that I'll never use. Not sure it'll fit in the Fiat 500, though…
One was £45 sold as "stopped working during storage" and the other was £20 and sold as incomplete.
The incomplete 2018 was missing its Frequency Standard board, but the oscillator was still present. The standard board divides the oscillator by 10,000 to provide a 1kHz reference to the synthesizer and handles the switchover to external clock source, too.
My first job was to see how badly messed up this incomplete unit was, by substituting the Frequency Standard board from the supposedly working one. This didn't make it spring into life. The computer did not appear to be communicating with the other boards, but was running and starting up.
Instead of swapping the board back I decided to board swap it until it worked but first I'd check the capacitors in the PSU.
Sure enough all the small Philips blue capacitors (22µF and 4.7µF) were well down in value (3µF and 1µF respectively), so I changed them. I also took out the chunky 15mF 16V smoothing capacitor for the +5V rail and somehow managed to misread it as 18.5µF, so I changed it. Later I put my glasses on and discovered that it was actually 18.5mF, I'd forgotten that the small tester I was using switches to milliFarads. I had tested the small capacitor on my Wayne Kerr B605 so I'm not sure why I didn't test the big one on that, too, but it was hot and I was tired and my vision was blurry.
I decided that as the computer comms problem was preventing anything from happening and limiting my diagnostic options I'd switch back to the other supposedly nearly working unit. This turned out to be not really the case, in many ways, but the computer *was* working and so was the front panel and something was appearing on the display. The output, though, was nothing because the reverse power protection was triggering once the computer finished booting. Removing the connector that contained the input to the RPP measurement diodes allowed it to boot but it was clear that the display wasn't right.
I decided to use the rebuilt-PSU generator as the project and the "working" 2018 as the donor, the deciding factor being the "working" PSU which had been modified for no obvious reason so the +5V adjustment range started at 5.25V and went up to around 7V, which I thought may have damaged some TTL or one of the divider ICs. This turned out not to be a particular problem but a duff keyswitch sealed the fate of the front panel and later I discovered that the frequency display had some bad segments (could be the decoder/driver chip).
With the Frequency Standard board now moved back to the more broken of the two I found that it would occasionally boot. Changing the CPU and reseating the EPROMs seemed to make it better but it always started up with an error indicating a bad checksum in the EAROM.
I also had no synthesizer lock, but it was switching between oscillators. There was no output on the front panel, though, only at the intermediate point where the RF comes from the synthesizer into the AM/filter/amplifier box. I took the easy way out at this point and substituted two divider boards in the synthesizer which brought back the fine steps but only above 32.5MHz. This meant that the BFO circuit was not doing its thing, so I changed that and got 80kHz to 32.5MHz back. The attenuator on this one seemed to be fine, though the output levels were all wrong, it was at least going through 10dB steps as it should.
Then I tried FM, but there was no FM at all. It seems that with an empty or corrupt FM calibration table the generator can't do FM. Additionally there seemed to be a problem with the FM/modulation oscillator board, so I swapped that over, too. After a very long calibration process with my trusty (slightly broken) 2305 I had working FM.
Now it was time to look at the output level, which seemed not awful on the BFO output but very poor at the UHF end, even with the calibration cranked up all the way. The output amplifier board had been modified due to excessive gain. Rather than back the mod out I just changed it and this brought back full level adjustment and amplitude calibration was a success with plenty of gain in hand. I didn't realise before, but these generators can easily do +20dBm with a bit of deliberate mis-calibration. AM calibration also worked but I wasn't able to stop it being a few percent over at UHF, so I may revisit that soon.
The front panel needed attention so I put together the best switch caps from both to give it a full set. Two LEDs were also not working, the AM indicator and the 6kHz modulation oscillator indicator. I changed both multiple times, turns out the + symbol on the silkscreen is on the cathode. No idea why but not the first time I've seen this on test equipment. I didn't have any 2mm LEDs for the 6kHz indicator or proper yellow 3mm for the AM switch, but I managed to pull the 2mm LED from the other front panel and have used a sort of orangey LED instead of yellow for the AM switch. It's actually the same colour as the switch, which almost made me change all of them…
I'm now trying to get the donor unit working to some extent, as I am sure I can bodge a Frequency Standard board quite easily and I'd like to get board level fixes done where possible.
I had originally intended to sell the 2018 at McMichael but it wasn't ready in time - just the LEDs, really, but I'd worn myself out and had little sleep, hadn't managed to get to to the storage unit to grab some other items I wanted to sell. I may make it to MK to sell, though. I'm definitely keen on getting rid of my 853/8558 (with bonus broken 8559 and incomplete 8557 in flatpack form), possibly my 3325B, because it's a hateful thing that breaks whenever I need it, some Fluke 8502 ac meters, maybe my RACAL 1992 and 9300B and a few boxes of components that I'll never use. Not sure it'll fit in the Fiat 500, though…