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