SB-104A Counter Circuit Board

[JF]

On 10/6/05 Jan SM7NDX wrote on the Heath list:

 >Were to buy 74H103 (IC-101 at the Counter Circuit Board in a SB-104A)?
 >Heath partnumber 443-70.
 >I think that the IC-101 (74H103) is not working properly.
 >73 de SM7NDX, Jan


Could be the IC, but the counter board in the SB104A has some other
places that need to be checked before you start replacing IC's:

that board has numerous sockets for the IC's, and those sockets have
been a continuous source of problems because of poor contacts. And,
because the sockets were soldered in by the kit builder, solder flux
tended to wick into the contacts, causing more intermittent non-
conducting faults that can be frustrating to find and then re-occur
over and over again. Often simply removing an IC and re-inserting it
would fix a problem temporarily, but then it might go bad again later.

So, you should first remove all the ICs, clean both their legs AND the
socket pins with flux remover and then contact cleaner, straighten the
IC legs and bend them out slightly so they have a little spring action
when they go into the socket (to ensure the tension will help make
contact). Make sure none of the sockets were soldered in backwards, and
that none of the ICs were inserted backwards.

Next, you need to tighten all chassis screws in that area to make sure
they make a good ground contact, clean the board connectors that plug
into the chassis, and the chassis contacts. More possible sources
of problems are the small electrolytic capacitors, which may get leaky
with age. Check the board voltages listed in the manual, as they may
reveal defective components.

These things may or may not fix your problem;  those IC sockets are
difficult to deal with - heat and vibration can make the board flex in
use and that can sometimes cause the ICs to move ever so slightly in
their sockets, which might cause a contact to loose conduction if there
is any oxidation or dirt or solder flux in it.

The sockets on my SB-104A counter board caused so much trouble that I
finally removed all of them and soldered the ICs directly to the board.
Fixed the problem, but not having sockets makes it harder to do
troubleshooting if an IC goes bad later. You might consider buying some
high-quality sockets and replacing all of the originals. Try to find
some with gold-plated contacts that are closed at the bottom and will
not allow solder and flux to wick into the contact areas.

Another place in the counter chain that can cause similar problems is
the display board behind the frequency display.  WB8VGE on the Heath
list last year was going to sell a replacement that uses LED frequency
readouts instead of the original gas-discharge types - that would be a
worthwhile modification because then you could remove the HV generator
for the display, which would eliminate the birdies that it generates.
For this you might try E-mailing:

         Mike Bryce, WB8VGE    (E-mail   prosolar at sssnet.com )
         SunLight Energy Systems
         http://www.seslogic.com
         http://www.theheathkitshop.com

If you want to replace the IC, NTE at     http://www.nteinc.com
has a cross-reference lookup at
http://nte01.nteinc.com/nte/NTExRefSemiProd.nsf/$$Search?OpenForm

For the 74H103, NTE lists their part # NTE74H103.

They list distributors in Sweden at
http://www.nteinc.com/NET_St_lst/sweden.shtml

Other countries at
http://www.nteinc.com/NET_St_lst/INTL.html

Mouser Electronics in the U.S. has it.  Also, doing a Google search with
keyword 74H103 will turn up quite a few sources of parts and information.

73

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