Newsgroups: rec.radio.info
From: wa2ise@cbnewsb.cb.att.com (robert.f.casey)
Subject: TH78 mods for newer radios
Message-ID: <1993Feb11.024318.5494@cbfsb.cb.att.com>
Keywords: mods
Sender: news@cbfsb.cb.att.com
Organization: AT&T
Date: Thu, 11 Feb 1993 02:43:18 GMT
Approved: rec-radio-info@ve6mgs.ampr.ab.ca
Lines: 81


From: Brendan_Hoar@notes.pw.com
Subject: Newer TH78A modifications


This contains the mod information for the NEWER Kenwood TH78A.
-------------------------------------------------------------------------
From: gwalsh@kilroy.Jpl.Nasa.Gov (Gerald J. Walsh)
Date: Far too long ago.
>I have a friend who just purchased a TH-78A and tried the mods that, by
>now, we all have a copy of.  He says that his radio has two green wires
>near the diodes that are, "just asking to be cut"!  From the
>experimenting that he has done, cutting one wire is equivalent to
>removing D5 and cutting the other green wire is equivalent to cutting
>D6.

I followed the traces by sight and I would agree with you.

>With the "CAP/Mars mod" completed (remove D6 or cut the green wire) he
                                                        ^lower (W2)
>does get the expanded RX range, but he gets no TX capability outside
>the amateur band.
>
>Alternatively,
>
>With the "Beyond MARS mod" completed (remove D5 or cut the other green
>wire) he gets the full RX capability and the extended TX capability for
>the CAP/Mars mod, not the full TX capability expected!?
>
>BOTTOM LINE:
>
>Is anyone aware of a change in the mods for later versions of the
>TH-78A? We are not able to fully expand the TX capability of this
>TH-78A.  We compared (by voice) the mods we made with another ham who
>modified his. We did everything properly....

I just got the ARTSCI 5A techmod book.  They replaced the 
page that contains the Alignment controls for the TH-78A with a mod page for 
'Later Model (with green jumpers)'.

I haven't done a whole lot of experimenting, but I think the list below is 
true.  I've removed D3 D4 and D6 and have the associated capabilities.

Assuming that D1-D6 are all installed:
Remove D3 = Wide band xmit (maybe wide band rcv in addition)
Remove D4 = Cross band repeat
Remove D5 (or W1) = Mars/CAP
Remove D6 (or W2) = Wide band rcv

The book doesn't seem to indicate that D6 is necessary for wide band receive, 
so try removing only D3 (and D4 if you want) and see if you get all the 
capabilities.  If not, then remove D6 too.

D5 has priority over D3, so DO NOT REMOVE D5 if you want full xmit.  I had 
already made the mods for the OLD MODEL (which included the removal of D5) 
and had to resolder D5.

	Left VFO			Right VFO
50.000-85.2x (with beep)		50.000-110.xxx (with beep)
85.2x-179.995			110.xxx-179.995
300.00-399.975			
400.000-511.9875		400.000-511.9875
				800.00-999.9875

xxx is variable.  My guess is the beep is some sort of error notation of some 
kind, but what?  Someone, somewhere said 
it has something to do with the PLL...

At this time, I can't do the xmit testing since I don't have a dummy load 
here. 
We had a dummy load when we 
were testing the mod from the 5A book and the xmit opened up to much more 
than the MARS/CAP mod allowed.

Brendan
(No call yet - passed Tech exam on Jan 3rd)
========================================================================
Note: I haven't tried or verified this, proceed at your own risk.  And 
DO NOT transmit outside of legal bands!  WA2ISE
/EX