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Old 3rd Jan 2022, 11:44 am   #1
Stuartsjg
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Default Eddystone EC10, bands with no reception and added mystery component

Hello,

First post but I have used this forum for info previously, including already helping with this radio.

History, this unit was given to a former colleague and it sat in a meeting room for years and years never used, nobody claimed it and it was put to the WEEE skip! Needless to say I spied it and rescued it.

Hooked it up and found all 5 bands were silent, this forum suggested to lift the screens on the transistors which gave me some sound on all bands and audio received on bands 3, 4 and 5.

I had no time for dealing with it further so sold it. Unfortunately the courier played football with it so the buyer found it cut out once the RF gain was over 30%ish.

So, I have it back, and changed out all the OC171's for AF178's - this restored full range of gain on the RF dial.

I've picked up signals on bands 3, 4 and 5 but nothing on band 1 and 2.

Still to do the voltage checks.

I have replaced the caps in the AC supply as they were dead, replaced the 500uF 30V for 2 x 470uF 25V and the 1000uF 12V for 2 x 1000uF 16V (as modern electrolytics are a fraction the size!).and this made massively reduced the mains noise. To check it further, I hooked up a 12V battery to the rectifier output so I had a perfectly clean supply and referenced to ground rod for the set.

Still nothing on band 1 and 2, the occasional band of noise so they are not dead, just not getting any reception.

I've been familiarising myself with the boards and schematics (I am an electrical engineer and day to day by profession work with PCBs and schematics, just not radio!) and found some parts have been added to the BFO section a 7803B 8-legged metal can component. Nothing conclusive coming up online.

Couple of questions out of my story so far which I'm hoping for help with...

1) any good pointers at what may be killing the two higher frequency bands?

2) in the UK / North East Scotland, are there any reliable strong stations I should be able to pick up in all bands, with and without CW and BFO?

3) what may be going on with the 7803B being added?

Any info or help will be appreciated, I'll update with the voltage analysis.

Thanks, Stuart G
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Old 3rd Jan 2022, 12:26 pm   #2
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Default Re: Eddystone EC10, bands with no reception and added mystery component

7803 sounds more like a date code than a part number. Online references mostly refer to a "Lockout" relay!


Metal can and 8 legs could be almost anything from a miniature relay to one of the Plessey SL600 series RF ICs.....


A picture showing its location might help.
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Old 3rd Jan 2022, 1:51 pm   #3
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Default Re: Eddystone EC10, bands with no reception and added mystery component

7803 could well be a date code, i.e. 3rd week of 1978- are there any other discernible characters on it? Plessey did a range of comms ICs in metal cans, maybe one of these as product detector?

Crossed with H1360!
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Old 3rd Jan 2022, 2:42 pm   #4
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Default Re: Eddystone EC10, bands with no reception and added mystery component

I'm expectng that to have SL623 on it somewhere.
PLessey AM Detector, AGC Amplifier and SSB Demod

Or maybe SL624 Multimode Detector whch could do FM as well.
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Old 3rd Jan 2022, 3:40 pm   #5
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Default Re: Eddystone EC10, bands with no reception and added mystery component

Many years ago, John Birkett used to sell Plessey reject ics, he called them "Communication Series" istr.
Weren't marked with the SL*** number, but might have had a code number on them? Somehow, he knew which was which. I still have some, somewhere.....
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Old 3rd Jan 2022, 4:30 pm   #6
Stuartsjg
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Default Re: Eddystone EC10, bands with no reception and added mystery component

Thanks for the comments!

First post had two photos attached, one of each side.

I'll pop the board out and get a better look, wanted to do the DC voltages first before I took it apart.

Much appreciated, Stuart
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Old 3rd Jan 2022, 10:06 pm   #7
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Default Re: Eddystone EC10, bands with no reception and added mystery component

I have only the circuit for the Mkll - ten wafers on the band switch! Have you given them a gentle clean with an appropriate cleaner - preferably with a cotton bud - if the wafers are paxolin then they may take ages to dry out. That may stop an oscillator or change the tune of an RF stage.

There's no sign of an IC in that diagram, only germaniums!
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Old 3rd Jan 2022, 11:59 pm   #8
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Default Re: Eddystone EC10, bands with no reception and added mystery component

Hi,

Good shout about cleaning the wafers, will get that done.

The mystery Plessy part is SL640C and its been quite cleverly built into pick up existing tracks - clearly a practiced mod!

Some photos are attached, as well as my attempt to retrace the circuit. Need to follow wider where the connected wiring goes.

Not at all sure what this is supposed to do or what effect it would have on the operation?
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Old 4th Jan 2022, 12:05 am   #9
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Default Re: Eddystone EC10, bands with no reception and added mystery component

Checked the voltages, was done with modern DVM so probably much higher impedance than what the set was tested with, that said, the source resistances are all quite low so probably no big impact with a different meter.

Test done with 12V battery supply into AC module zener, 9.2V resulting on the 9V bus and 6.6V on the RF supply.

All readings in the table are mV. Some which were far off ive rechecked and they are correct. Not yet checked surrounding resistors to see if any are off.

I think for the most part it shows the newly fitted transistors are all functional as a dead one or misfitted i would expect to see things hitting the rails.

Thanks, Stuart 🙂
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Old 4th Jan 2022, 12:18 am   #10
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Default Re: Eddystone EC10, bands with no reception and added mystery component

Ah-ha!

Found the attached, certainly explains things! Probably not the issue with my reception on other bands.

Are there any broadcasts which use BFO for me to test with?

Thanks, Stuart
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Old 4th Jan 2022, 9:03 am   #11
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Default Re: Eddystone EC10, bands with no reception and added mystery component

You did well to find that and I should not have overlooked the SL640 double balanced modulator in post #4.
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Old 4th Jan 2022, 2:23 pm   #12
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Default Re: Eddystone EC10, bands with no reception and added mystery component

It seems to be using the BFO signal from TR6 and the IF signal as inputs but the sketch does not show where the output goes to. It is effectively a Product Detector.

I assume the output goes to the audio amplifier.

You can test it by tuning into some SSB signals and then turning on and adjusting the BFO for maximum intelligibility.
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Old 5th Jan 2022, 12:11 am   #13
Stuartsjg
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Default Re: Eddystone EC10, bands with no reception and added mystery component

Hi,

The output needs traced, it goes upto the BFO switch and joins in some other coax which i assume is AF.

Do you have any pointers for frequencies or stations i should look for which operate SSB to test? Ideally in the lower frequencies until i resolve whats going on with the higher bands. Dug out my Atlas LCR meter from about 15 years ago and got it running to start checking things.

All the best, Stuart
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Old 5th Jan 2022, 6:35 am   #14
M0AFJ, Tim
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Default Re: Eddystone EC10, bands with no reception and added mystery component

Hi Stuart, I don’t think you will find any broadcast stations that require the BFO, they run AM, however there are two Volmet stations which are very strong around the U.K. transmitting USB in the 5MHz band.
Hope that helps
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https://en.wikipedia.org/wiki/VOLMET

Last edited by M0AFJ, Tim; 5th Jan 2022 at 6:37 am. Reason: Adding more info
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Old 6th Jan 2022, 3:49 am   #15
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Default Re: Eddystone EC10, bands with no reception and added mystery component

As Tim says - two Volmet ("Vol" = flight, "Met" = meterological ) broadcasts which are going almost continuously. Shannon on 5505kHz USB and the RAF station on 5450kHz USB which used to be Northolt but now I think it's down in Cornwall, RAF Station St. Eval. Trenton, Canada is a good catch on 6754kHz.
If I can hear them in NZ occasionally, you should have no problem!
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Old 18th Jan 2022, 2:19 pm   #16
Stuartsjg
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Default Re: Eddystone EC10, bands with no reception and added mystery component

Hello,

Been a while since i had a good chance to get back looking at this. I made up an outdoor aerial, 20m of wire running N-S with ground rod hooked upto some coax to run into my garrage.

I also got the contact cleaner out and polished up the wafers using a sheet of paper to rub the contact faces without getting too invasive.

Another tweak, as well as changing out some of the DC bulk smoothing caps, i also wired an external DC supply to the rectifier output so I can run off a 12V battery or my bench supply which are much quieter.

Massive difference on band 5, others are still not great but i think the wafers need more attention as sometimes i need to click back and forward when changing bands to get a sound from the speaker.

I've attached a list of what i picked up on band 5 but I need to work through the others in more detail. I found webSDRs very useful as a reference for frequency and working out what i was listening too.

Interestingly, as 4 and 5 have an overlap at the bottom and top end, i had thought i should get high end 5 at low end 4, but that was not the case.

If I need to do an alignment (after I've done more work on the wafers) I hope a former colleague may have this kit, else I seen the likes of https://www.vintagetvandwireless.com/radio-restoration as perhaps an option if i was stuck. Other options are likely available!
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Old 21st Jan 2022, 8:11 pm   #17
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Default Re: Eddystone EC10, bands with no reception and added mystery component

"Garbled talking" on 3788kHz will probably be a radio amateur using SSB on the 80 meter band. Did you try to resolve the audio with the BFO?
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