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Old 17th Jul 2020, 5:24 pm   #1
dennis998
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Join Date: Jul 2020
Location: Craigavon, County Armagh, Northern Ireland, UK.
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Default Datong FL1 Audio Filter

Hi all from a newbie to the forum.
A few nights ago I fired up my old FRG7 for the first time in several years and, while that is operating fine my Datong FL1 Audio Filter appears to be dead. I've done some basic connectivity and power checks, cleaned switches and so on, but would need a schematic to trace the circuit.
A search on the net for this has come up empty. Anyone able to help me out with this?
Best regards
Dennis
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Old 17th Jul 2020, 6:13 pm   #2
Dave757
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Location: Scratby, Norfolk, UK.
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Default Re: Datong FL1 Audio Filter

Hi Dennis,

Welcome to the forum.

If you Google Datong Archive,, then select FL1, the site has PDF's
of the manuals and schematics available to download.

Kind regards
Dave G0ELJ.
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Old 17th Jul 2020, 11:20 pm   #3
dennis998
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Default Re: Datong FL1 Audio Filter

Many thanks Dave, this is just what I need.
I can't understand why my searches didn't throw up that site. This will keep me busy for a few evenings.
dennis
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Old 18th Jul 2020, 11:26 am   #4
Dave757
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Default Re: Datong FL1 Audio Filter

Hi Dennis,

They are a nice filter, but I found that it took a bit of getting used to.
I believe that on some of them the power connector was the same
as one of the others, which could give rise to power being applied
where it shouldn't be!
Mine is modified to a concentric socket.
Good luck with the repairs.

Kind regards
Dave
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Old 18th Jul 2020, 3:44 pm   #5
dennis998
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Default Re: Datong FL1 Audio Filter

Hi Dave.

Yes, my FL1 has the duplicated DIN speaker-type sockets but, like you, I'd modified this to a low power DC socket, with a voltage regulator to tame a 3Vp-p sine wave on a supposedly DC wall-wart.

I've made a start at tracing and a 1khz sine wave seems to make it as far as the input to the TBA820 output IC whether the filter is switched in or out.

Operating the controls and pushbuttons more or less at random alters the shape and/or amplitude of the signal reaching the TBA820 so I'm hoping the remainder of the unit is OK and that the fault is in that IC or its associated R's and C's. A bit happier with that, I wasn't looking forward to tracing the filter logic.

Additionally the TBA820 runs quite warm and pin 12 of the IC is at near Vcc potential so all pointing toward an output stage fault.

Regards, Dennis.

Last edited by dennis998; 18th Jul 2020 at 4:02 pm.
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Old 18th Jul 2020, 6:57 pm   #6
G3PIJpeter
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Default Re: Datong FL1 Audio Filter

I have two of these filters and find them very effective, especially for CW. However, when first acquired, all the pots were extremely scratchy and needed treatement with de-oxit. In the end, I replaced two pots on one filter and one on the other. I don't think that the originals are of particularly good quality.
- Peter
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Old 5th Aug 2020, 1:07 am   #7
dennis998
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Default Re: Datong FL1 Audio Filter

Job done. I had a bit of trouble sourcing a (long obsolete) 14 pin TBA820 and had started making a piggy-back board to take an 8 pin version when good old Cricklewood Electronics came up trumps. IC replaced and performance back to normal.
Oddly I could find no other fault that led to the demise of the original IC. Old age?
dennis
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