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Hi all I have just finished repairs to a faulty spare Marconi 2955 I have had lurking. Mostly stock faults, 1 OM345 dead on AA4 (unusually, the 4K7 external resistor fix did not work with this one, I had to build up and fit one of my substitute boards with a Mar7) The main PLL would not lock, The fault was C108 a 220uF electrolytic capacitor in the loop filter on board AA3 short cct The interlink sliding connection between AA3 and AA4 was in need of a clean and a new one. Symptoms were no carrier output below 88MHz (just low level wideband mush) Errors 11 25 and 27 on the self test Confirmed no 200MHz oscillation after poking about on AA4 I confirmed that the switched -12V was not good At the collector of TR6 there was only -2.5V (when the selected frequency was lower than 88MHz) and nothing the other side of 22Ohm R50 (which was running a bit hot) The fault was another 220uF electrolytic, C59 same type as C108 It too had failed short cct Replaced the electrolytic and the switched -12V rail was ok after R50 All Self Cal tests now passed everything seems good. Regards Mark GM4ISM http://dc2light.co.uk -- This email has been checked for viruses by AVG antivirus software. www.avg.com

Hi All, I was recently given a Marconi TF 995B/5 FM/AM Signal Generator, the person did not know much about it, and the unit looks in great shape. When I got it home and opened it up, I noticed two tubes were missing in the base of the power supply. The rest look in good shape, but untested. If possible, I would really prefer to get my hands on a copy of the exact manual for this unit. If anyone has a copy, can you please reach out to me? I have found copies of the manuals for the following two models: * TF 995A/5 -- Power supply differs from the TF 995B/5. * TF 995B/2 -- Power supply unit looks similar in layout to the TF 995B/5. However, looking at the markings on the power supply top board, I see: * 5Z4G, Full-Wave Rectifier * 6AL5, Double Diode So I need to track down one 5Z4G and one 6AL5. Can I go off the substitutions listed in the TF 995B/2 manual? Is there anything else that I should know about this unit? It is the first tube-based signal generator I have owned. Many thanks Brendan

Hi all can anyone help me with the 6590 Gunn power supply service manual regards Paul

Ok, next problem…. I have a couple of 2955’s both with the same issue which originally came to light as a wobbly sig gen. On further investigation, the output from the AR1 is unstable with about 300mV of ‘ripple’ at relatively low frequency. The voltage dips but a few hundred millivolts every 50mS or so. It’s not related to the AC mains as it still does it when fed from a DC bench supply. I’ve replaced all the caps, but no improvement. One of them had a shorted diode on the -12V rail, but again, replacing it made no difference to the main problem. It’s as though the regulator is overshooting and causing it to ‘hunt’. I was tempted to play around with the damping but thought I’d ask if anyone had any ideas before I get too carried away. Cheers, Pete

Afternoon. Proud owner of my old 2022E which needs OM 345s. I would buy all 11 to see me out but could not use all the other types. That may be the case for many owners. Is there any chance of me buying all or some.? Chris Browne

Hi, I have trouble with my Marconi 6960b power meter. It shows Err2 with power up, and does not find a power sensor. But it is connected. I have seen that some have problems with the power sensor cable. Measured it with an ohm meter and found out that some GND contacts are not connected ( A / F /J K ), but the GND E is connected. So it seems ok on the first view. Sensor was also not overdriven. That problem occurred for the second time, it worked in between, so it looks a bit like a mechanical issue. Any Ideas welcome, as I did not open connectors and head as I am afraid to disturb them. Jens DF5HC

I have two Marconi spectrum analysers and a spare display unit: 2383 100Hz - 4.2GHz 2386 100Hz - 26.5GHz 2380 They were bought at auction from the Marconi Stevenage factory a few years (maybe 10) ago when they finally emptied it. When I last looked the displays on the analysers were showing sensible stuff. The two analyser pairs have the interconnecting cables. The whole lot is yours for free - the only snag is that I'm in SW Scotland (about 20 miles west of Dumfries) and you will need to collect and be strong enough to carry them out ! Pictures here: https://www.dropbox.com/scl/fo/gj2mlqch8ocyffs5wbzdc/ACmVKN9Q3dZhOiu7jAb58Ko?rlkey=qq2r5ifehqcgwqdvqkyeh7fh0&dl=0 If you fancy them please email me at mk@... Michael Kellett

Hi Andrew, I sent you a direct email several days ago and have heard nothing further so it may have gone to your junk/spam folder. Regards, Kevin VK2KVJ Sydney, Australia

Greetings! I recently acquired a 2947 in excellent condition. It was failing the narrow-band power self tests, which is was an easy fix by re-flowing the input attenuator SMAs. Since then, everything has been working beautiful except for one thing: the internal reference is off by a bit. Normally I wouldn't be too concerned since I have a quality GPSDO/10MHz distribution amplifier feeding all my lab equipment. According to the 2945 service manual, simply connecting a 1MHz or 10MHz reference of 1mV P-P or above should be all that's necessary to "nudge" the internal reference. Unfortunately, connecting my 10MHz reference to the external reference input seems to have no effect whatsoever. It's a clean 10MHz 13dBm signal so it should be more than sufficient. Is there anything I'm missing? Kind regards! Dieter

First my apologies to the Marconi purists here, but I have no where else to turn. Adret were purchased and closed by Marconi, and I know some members here have Adret 742A instruments from past posts I am looking for schematics/circuit descriptions regarding my Adret, which has developed a fault in the 0.1 to 5dB attenuator, and I have traced the issue to the CPU board data bus feeding SN29 and SN20 with erroneous data! However I doubt the issue is with the CPU board as absolutely everything else is working 100% KO4BB has these manuals, but it seems it is effectively down so I cant access them. Does anyone have a copy of the manuals they are willing to share with me. Many thanks and sorry for the slightly off topic request.

Hi All, I have just aquired a 2030. When I first powered it on the display was very dim. Adjusting the contrast improved things slightly, But I guess the backlight is dying ? Trying it later in the day I just got a black screen , however the screen test function on power up seems to work. Any ideas please ? Regards Alan

I got an eprom programmer and i am wondering if i can upgrade my instruments to the last version, any advice ?

Hi all, I've encountered a strange issue with my recenty accuired 2440. After receiving it, I've tested it with first the internal oscilator and later with the external 10MHz GPSDO and it worked perfectly. Yesterday I started it up again with the usual setup (2019A) at 1 Ghz and it acted strangely. The indication was off by 200Mhz and running wildly in the last digits. So I tested channel A with 50Mhz and it was also off. Channel B had the same issue. and ofcourse channel C would not work. I've checked the voltage and they were +4.7,-4.7 and 10.3 Volts. Reseated the boards, cleaned the contacts but no avail. One strange observation was that channel A on the low side 1MHz did lock but higher gave the stange behaviour. Left it open in the shack (with the covers off and not plugged in the mains) and this morning I had the intention to methodically fault check it and it work again. One thing to note: Yesterday the temperature in the shack was 30C and now it is about 20C. So the questions are: 1. Could this be temperature related? 2. Or has anybody seen this sort of behaviour in general Greetings Kees Hofwegen

Hello - Ive got an old TF2304 with an odd problem. Im not sure if its a design flaw, or somethings faulty. It reads AM and FM modulation levels OK, across the whole frequency range. The problem Arises when I put in a FM signal, say 100kHz Deviation (1kHz tone, 10MHz carrier) the Meter reads 40% AM modulation. And Looking at the IF output, I can see the AM modulation. Ive checked: * My sig gen (its purely in FM mode) * LO levels and frequency range. I can see the AM signal at the output of the mixer! Blue is the IF output from the front panel connector Red is the Mixer output on the gate of TR5 any help greatly appreciated. Leon WW0R

Hi, Has anyone found a replacement for the LCD screen used in the 2945 service monitor? Epson ECM-A0310-1 or stock of the Nan Ya LTBRCT351FS Which was mentioned by George Edmonds a few years back? Looking for one or 2 to repair 2x 2945 service monitors in Australia. Regards, Andrew

Hello everyone, thank you so much for this impressive group dedicated to Marconi-IFR instrumentation. I recently acquired an IFR 2025 signal generator in excellent condition. However, the access passwords appear to have changed, as neither "1234" for Level 1 nor "123456" for Level 2 works (Err 173: Units not valid). My IFR 2025 instrument has the following serial number: 202306788 with a manufacturing date of 0531. I believe there is someone in these groups who can generate the factory password to unlock Levels 1 and 2. It would be great if you could help me with this matter so I can view the data and make adjustments to my RF generator. Thank you all in advance. Israel Roman

Hello, I have a Marconi 6200A without any sensors but the frequency counter and signal generator work well except that it is way off frequency. I would like to reset the internal reference or failing that supply an external reference. Can someone please supply a master password because I have checked the service manual on Page 3-287 and it appears that level 1 and level 2 passwords are user set so I have no idea what they would be. regards Noel

hello i have changed the buffer battery and now to enter the correct date it asks me for the 4 digit passqurd ( which i don't have ). can anyone in the group help me? the serial number of the instrument is 310213/001 type No 52871-900 thank you.

I have two Marconi 2440 counters, both with input problems on the high frequency input. One has no internal 10MHz oscillator, and it needs an external reference. $200 USD/ea. Shipping by Canada Post from Alberta, Canada.

Hi All, My 2955B has a collapsed (smaller writing) 3rd line on the display screen. I believe it has something to do with the vertical amplifier on the screen circuit. But only visible on the 3rd line from the top. This fault is intermittend, sometimes it is perfect and sometimes smaller. Has anyone experienced this, and maybe have a possible idea where to start looking. I suspect maybe a bad capacitor on the vertical amplifier? Regards Arthur