Newsgroups: rec.radio.info
From: wa2iseSubject: TH78 mods for newer radios
Message-ID: <1993Feb11.024318.5494Keywords:mods
Sender: newsOrganization: AT&T
Date: Thu, 11 Feb 1993 02:43:18 GMT
Approved:rec-radio-infoLines:81

From: Brendan_HoarSubject: Newer TH78A modifications This contains the mod information for the NEWER Kenwood TH78A.

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From: gwalsh
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