ALINCO DX-70 LOW output

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K3ICH:
Which diodes are you referring to when you say they're the cause of the low output/filter problems with the Alinco DX-70?

I have one in which the 160 meter lowpass filter is always engaged regardless of which other filter is also switched on for different bands.  The control line BB0/BB4 into the filter board's ribbon connector from the serial to parallel chips (uPD6345's), never goes above 8 Volts on the 160 meter (L0) line.  All the rest, L1 - L5 go to 12 V.  This keeps the upside down PNP transistors which control the IN/OUT relays on that filter turned on.  I can force the line to 12 V so that all the other bands will work fine, but then 160 never switches on.

There are two double diode packs which combine BB lines L0 & L3.  L3 by the way works fine.  There are also diodes across the relays and probably others.  Which ones cause the problem?

Thanks, charlie k3ICH

 

K3ICH:
Which diodes are you referring to when you say they're the cause of the low output/filter problems with the Alinco DX-70?

I have one in which the 160 meter lowpass filter is always engaged regardless of which other filter is also switched on for different bands.  The control line BB0/BB4 into the filter board's ribbon connector from the serial to parallel chips (uPD6345's), never goes above 8 Volts on the 160 meter (L0) line.  All the rest, L1 - L5 go to 12 V.  This keeps the upside down PNP transistors which control the IN/OUT relays on that filter turned on.  I can force the line to 12 V so that all the other bands will work fine, but then 160 never switches on.

There are two double diode packs which combine BB lines L0 & L3.  L3 by the way works fine.  There are also diodes across the relays and probably others.  Which ones cause the problem?

Thanks, charlie k3ICH

 

Alfred H. Poquette Jr.:
The diode is on the 1st filter board, BB0/BB4. The diode in question is on the BB0 side in the upper left corner.  Easier to just replace the board with a new one.  Burghardt's have these boards for just a few bucks.  They have a different type of diode on them.  I replaced the first four boards with the new ones.  Didn't mess with the fifth board as it's the 6m one and don't use that band but may replace it in the future.  Not a bad job if your proficient at soldering and de-soldering.  Too bad they didn't make these to where they just plug in.

Lee Sutherlan:
I may be having the same problem. Are these filters on the main board rather than the filter board? I will have to order from Alinco parts dept and want to order all 5 of them.

Clark McDonald:
If the problem is in the filter section, temporarily bypass the filter section on the test bench into a dummy load and wattmeter and check the PO without filter in the signal chain.  If power is restored, it is indeed the filter problem.

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