Here are some Questions and Answers I've gotten over the years about Exec II modifications:
At 07:10 PM 12/21/98 -0400, you wrote:
>My name is Max and my call is KP4PK. I am located in Arecibo, PR. I have >an Exec. II, >desktop version that I would like to duplex to be used as a repeater. It >is a 56 split version, presently operating what I think is a MARS >frequency. I have several questions that I would like to ask you. >1. Do I have to retune the TX and RX units? The new TX would be 145.17 >and RX 144.57. If I should decide to latter change frequencies, how far >apart from the old ones the new ones can be without retuning?
You'll need to retune. Even for a couple hundred kHz you'll need to retune. I've never taken one down that far... so you're results many vary. Look for clear peaks. You might get away with just a couple fine adjustments. Or you may want to do the full alignment. If an adjustment reaches an end before you see a peak, you may need to change some parts. The 56 version is rare, I've never seen one. It should go just fine with no parts changes. If you had the 66 version, I'm pretty sure you would have to change parts.
>2. I would like to keep the use of the front panel; use the volume >control with the front speaker and possibly relocate the squelch control >to the front.
Good plan. I've built one that kept the front panel. Use shielded wire for the Squelch control to be on the safe site. I didn't remote the squelch with that one, but I have with my main system. The controller I use has software controlled resistors, so I can adjust squelch from home. Very cool. I ran both pots in parallel. So the internal one is a course adjustment, the external is a fine tune.
>3. Do I have to do the jumper mod. to maintain the radio on channel one >or just keeping the channel selector knob on position 1 will do? Position 1 is fine.
>4. I have partial manuals for a mobile Master Exec II. Can I use these >>manuals for tune up or do I have to get a set for the desktop unit.
The RX and TX sections are the same. The SAS board is slightly different and the control panel will be missing. You shouldn't need more than the SAS pin-outs, which I have on my page.
Enjoy the project. Let me know how you do with the tuning. I will be interested to see if they'll go that far down.
And a follow up:
At 12:35 AM 12/22/98 -0400, you wrote:
At 04:28 PM 11/29/98 -0700, you wrote:
>Hi, I am an amateur radio operator in Banff Alberta. I recently bought a GE Mastr Executive II Base unit. It is currently crystalled for 140.925 MHz and I would like to convert it for repeater use. My surfing from site to site in an attempt to find additional information about this radio has led me to your web site, which by the way appears to be the most comprehensive GE Mastr Exec II site on the world wide web. You are obviously an expert. Based on what I've read on your website, I think I will probably go with the NHRC-3 controller and hope you won't mind me asking you a few questions.
After complements like that, of course not! But I'll share this with the repeater mailing list I moderate on Onelist.com. That way we'll all learn a bit. I hope others will talk about their experiences.
>Where can I obtain ICOMs for this unit and how much do they cost?
I get them at hamfests or extras in the radios I buy. Usually US$5-10. The nice thing about the Exec II is that any bands ICOMs will work on any band radio. I've used UHF ICOMs in a VHF radio with no problems.
>I am trying to obtain a service manual from GE (Erickson) but I haven't got one as of yet. In your documentation you mention cutting one side of CR906, where is CR906 located?
This is REAL hard without a drawing. I would scan them to my website, but I'm afraid that GE might not like the copyright infringement.
Locate the SAS board. Place it so the power transistors are at 9:00 and connectors most connectors are at 3:00.
At the lower right corner there's a pot (R906). CR906 is just above this pot... not the one to the left of the pot. It's a very small glass diode.
>You also mention jumping the collector and emitter of Q908, where is Q908 located on the SAS board and which leads are the collector and emitter?
This is real hard... There's a whole cluster of black transistors in the lower left quarter. It's about 3" from the left edge and 2" up from the bottom. Very close to it's right is 4 parts laying up/down. Resistor, resistor, diode, resistor. If you have the base station SAS, there's a coil/test point just below Q908. Short the top and bottom leads of this transistor.
>I do not intend to rack mount the repeater and will leave it in the existing case therefore, will I have to fix the ICOMs to always on?
If you want to keep the front channel selector in circuit, no need to install the jumpers on the SAS board.
>You mention connecting a coax from the duplexer to the receiver, where exactly should the new connector (SO239) be wired to and are there any other considerations that I should be aware of?
There's an RCA like connector on the cast section of the receiver, close to C301. If you have the UHS pre-amp, it will be right next to this jack and your cable will have to plug into the pre-amp first. Note that this is NOT a real RCA or phono plug. The center pin is shorter. If you use a real one you might bottom out and short it. Cut yours to match the one that came out. Use very well shielded coax. Try to route it away from the TX coax. I've used the cable out of another base station.
>I hope it is no problem for you to answer these questions, as you can tell this is my first repeater conversion and I don't want to screw it up.
These things are pretty easy to work on when you get the hang of it. I hope you have access to a signal generator and counter. Without them, it could be a bit tough to tune. I did my first ones with a handheld on lowest lower, under my bed in another room. ANYTHING to get a weak signal. As I tuned and needed less signal, I moved it farther away.
>ps: Have you every considered documenting and photographing, in full detail, a conversion of one of these unit and selling it as a Repeater Conversion Manual?
Sell? No thanks. Too much work as it is! Actually, the web site came from notes are for my use. When I started a personal web site it just made sense to put it there for everyone to see. I really have to be careful not to violate copyrights. I lost my digital cam, so it will be a while before I can show closeups of the mods.
>Once again thanks for the great website!
Thanks for the comments!
At 08:59 PM 12/29/98 -0500, you wrote:
At 07:55 PM 12/17/2002 -0500, you wrote:
I have four of these units and you are correct when you state
the weakness is the power supply. Two of my three UHF radios have the PS
problem. They go over-voltage and can cause some bad issues. I don't have a
manual to find the replacement parts, there are two TO-220 case transistors and
a T-09 pass regulator transistor. Do you know the replacements for these or do
you have a parts list, schematic on the power supply?
Thanks, Dan KA0OXH
I'm looking at the manual, but it's not going to help much.
The big one on the outside of the heatsink seems to be Q801, 19A116753P1 Silicon, NPN, sim to 2N5302. Written next to that, by hand, by an earlier owner of the manual is "SK9134"
The other two, Q802 and Q803 are 19A116118P1, Silicon, NPN. Not much to go on. I found them listed here: http://www.hallelectronics.com/getxt.txt But no more cross info.
Another part I've seen go is VR1, 19A115528P4, Zener: 1 watt, 6.6 mW.
Also the big caps, C810 and C802, 10A126770P106 Electrolytic: 2100 uF +/-75-10%, 35 VDCW; sim to Sprague 34D218G035JT0
Good luck. Let me know what you find.