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Old 3rd Jun 2014, 9:30 pm   #1
Wendymott
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Default Marconi 2022 Generator

Hi Peeps... One of my Marconi 2022 generators has had a serious malfunction. Last time I tried to use it.. it came on ok.. did the software check, then just "died". I found that the +5v source had failed and located the Pass transistor BD543 open circuit. I ordered a reasonable equivalent, re assembled, with fingers crossed........now all the front panel leds light, but no button functions or LCD display.
All the multi pin plugs are located correctly.

Before I delve further, has anyone any clues, to be honest it sounds a bit "terminal". All the supplies are spot on.....

Your comments would be most welcome.
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Old 5th Jun 2014, 8:37 am   #2
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Default Re: Marconi 2022 Generator

Which variant is it and do you have a manual for it? Some versions of the manual contain a fault-finding tree.
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Old 5th Jun 2014, 1:39 pm   #3
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Default Re: Marconi 2022 Generator

Hi Richard. The rating label states "C", but just 2022 0n the front panel.... I have the schematic, and have found the flow chart on my files........... the original question was "just in case" someone had knowledge of a specific fault, much like the OM amp problem.
Thanks for the interest... I will print off the flow charts and if I locate the problem I will post on here.
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Old 5th Jun 2014, 4:17 pm   #4
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Default Re: Marconi 2022 Generator

Wendy, other than the OM345 problems, the most common fault (causing freezing) that I have found is failure of the 10MHz ovened oscillator. It is in a small grey plastic case. The foam inside degrades and damages the trimmer cap.
Check with a scope to see if it has volts and is giving out 10MHz at a goodly level.
Everything runs off this including the processor!
Either replace or clean the cap - that got a few going for me.
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Old 5th Jun 2014, 6:18 pm   #5
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Default Re: Marconi 2022 Generator

Hi Jeremy... Thanks for that........... I will be looking at that toot suite....

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Old 7th Jun 2014, 3:07 pm   #6
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Default Re: Marconi 2022 Generator

Well peeps.... Both issues sorted....The cause of all the leds illuminating and no functions.. The main reservoir cap C1 15000uf was open circuit. I had removed it to test its value and ESR and upon replacement, assuming the pads were Plated through holes, had not soldered the + terminal to the pcb "its on the top side", to remedy this I had to use some solder braid from the cap terminal to the nearest pcb point.

The other problem, was that the "Reverse Voltage" legend would show and no button operation or output. The Reverse voltage detector is in the RF attenuator block, 2 diodes and two resistors, the 100R measured 110R and R16 1K0 was not measurable as it broke on removal. However replacing R16 with a new one sorted out the problem...I have now both 2022's back in service.
Thanks to all that commented.
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Old 7th Jun 2014, 3:46 pm   #7
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Default Re: Marconi 2022 Generator

Well done Wendy - nice fault-finding. But bad design to rely on the cap lead for a via!
The 2022s are real workhorses - mine was out just yesterday for a repair of a KW2000B transceiver.
Good result...
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Old 8th Jun 2014, 10:56 am   #8
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Default Re: Marconi 2022 Generator

Thanks Jeremy, its nice when things go right for a change..... as you say, bad design on Marconi's behalf.....ah well back to the Hammerlund HQ170..
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Old 8th Jun 2014, 7:19 pm   #9
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Default Re: Marconi 2022 Generator

I must protest on behalf of designers long-gone! The pth must have been faulty or damaged. Having worked for Marconi Instruments for 14 years about the time the 2022 was designed there is no way such dodgy practises would have been allowed. Although one or two slight misdeameanours did occur.....
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Old 8th Jun 2014, 7:53 pm   #10
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Default Re: Marconi 2022 Generator

Well done Richard - I withdraw my accusation! I have found the 2022 to be an excellent sig-gen, although the choice of those pesky OM-345s was in retrospect a shame. The OM-345 was really intended for low-ish cost consumer devices (TV masthead pre-amps) not high-quality testgear.
I did chat to a chap who was product manager for the 2022s a while back. He confirmed that the 2022E variant, designed for an MOD contract did have a few cost-saving "features" compared to the commercial 2022A/C/D versions. But I am sure that did not include non-pth vias.
Anyway, Wendy's machines are back working so that's an excellent result.
(And Wendy has no doubt already discovered that the construction practices inside the Hammarlund HQ170 are not of the same standard as the much later and professional 2022!)
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Old 9th Jun 2014, 5:04 pm   #11
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Default Re: Marconi 2022 Generator

Ooppsss did not intend to cause controversy....... When I took out the cap, its top plastic cover was bulging out.....thus I suspected it trying to "gas out"... however the value and ESR were ok, so I cut off the top and the ally case was intact.....When replacing the cap, I did not notice the PTH contact had disappeared, however its fixed now..... until the "next time" whenever that is...... The 2022 is much smaller physically than my Adret which was a Marconi copy with incremental frequency dial, and I can repair the 2022, the Adret has gone to the great "Junk box" in the sky
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