All: Here is a copy of some of the hints I received regarding this problem, plus what I found:
As I expected, the .01 microfarad cap across the accessory jack was already installed; my manual had an addendum covering this, so no surprise. I removed the PS7 voltage/current sense board from the power supply. This is easier if you just unplug the small regulator just to its right. I stupidly unscrewed the regulator and had to carefully reinstall it, taking care to use thermal compound, the transparent plastic washer, and the black plastic spacer under the mounting screw. I measured the 5-k current set pot (two terminals are common). It was set at 1.915K (not removed from the board). I set it at its physical midrange, 2.1K, on the hunch that this would be approx the design 25-A limit. I did not test the power supply with a power resistor, but did clean up all the board and regulator connections. I powered up the TR7A and adjusted the voltage adjust pot in the PS7 for exactly 13.6V in receive (it was 13.68V). After all of this, I tried some test transmissions into a dummy load. The wattmeter in the TR7A appears to be a bit scotch on 40; there is some delay in the indication, so it's easy to be fooled, although it's pretty close if you wait for it to settle out. I can easily modulate into the dummy or real antenna to the point where the ALC green LED blinks. The power supply will kick out if I use a hot mike and run the mike gain up too high - but that isn't a real problem. I think the original problem was more due to my looking at the TR7A wattmeter and trying to kick it up to 30 W or so, rather than looking at the ALC LED and external wattmeter. Note - the lights still dim a bit more on 40 than on 20 at full power - I may look at the low pass filter on 40 to check if there is a component problem, but at least the rig is usuable now on 40 SSB and CW. The external wattmeter indicates 145 W out on 40 CW with no problems, and the internal meter is close after it slowly stabilizes. Note that the scale between 100 and 200 W is highly compressed. If I get ambitious, I may do a better job of adjusting the current limit pot in the PS7 and checking the low pass filter, but there are other projects more pressing. Hope this helps if you have the same problem, which seems to be a common one. Thanks to everyone who replied, especially Gary (see below). 73, Rocco N6KN ----- Original Message ----- From: "Rocco Lardiere" <[EMAIL PROTECTED]> To: "Gary Poland" <[EMAIL PROTECTED]> Sent: Saturday, July 05, 2003 5:17 PM Subject: Re: [drakelist] TR-7A trips off on 40 SSB > Gary, > > Many thanks for the tips. Sounds like I am not the only one to encounter > this sort of thing. > > I had adjusted R1613 on the Predriver board for 145 W out on 20, per section > 3-12 of the service manual. Perhaps this is pushing it a little too hard. > I also had adjusted R2210 for proper ALC action, and operation is as > expected, except for the current kickout. I will try to back off a bit and > see if that does the trick. > > Now that I have pulled out my reading glasses, I see that the overcurrent > protection limit is set by a 5 k pot in the PS 7, which may or may not be > set correctly for 25 A tripping. I will at least check that pot's > resistance (3.9 k in the schematic). Perhaps it is set a bit low, or > perhaps the resistors in series with it have drifted a bit. If the PS-7 is > set a bit low, and the rig is especially hot on 40, that could account for > what I am seeing. I could put an ammeter in there, I guess, to see what is > happening. One thing I do note is that the lights dim a bit more during 40 > m operation, indicating high current draw. > > BTW, I am not using the accessory 12-V jacks, but I will check to see if the > recommended .01 cap is in place across that line. > > However, I have not checked the pin diodes. Forty meters is definitely a > hot band as far as transmit on this rig. I was thinking that I might have a > problem in the low pass filter section, leading to less efficiency. I will > check the copper grounding clips, also. > > I appreciate the information very much! > > 73, > > Rocco N6KN > ----- Original Message ----- > From: "Gary Poland" <[EMAIL PROTECTED]> > To: "Rocco Lardiere" <[EMAIL PROTECTED]>; <[EMAIL PROTECTED]> > Sent: Saturday, July 05, 2003 2:14 AM > Subject: Re: [drakelist] TR-7A trips off on 40 SSB > > > > Rocco, > > It has been my experience that TR7's can draw excessive current > especially > > on 40 meters if any of the copper spring grounding clips are missing or if > > you have a leaky pin diode on the low pass filter board. Also make sure > that > > your ALC and PA drive are set correctly. The pot on the predriver board > > should be almost full CCW, just giving enough gain to get ALC on ten > meters. > > Key down output should be between 120 and 140 watts on 20 meters. TR7's > can > > become unstable un 40 meters especially. > > > > > > 73, Gary > > > > > > > ---------------------------------------------------------------------- Submissions: [EMAIL PROTECTED] Subscribe: [EMAIL PROTECTED] - subscribe drakelist in body Unsubscribe: [EMAIL PROTECTED] - unsubscribe drakelist in body Hopelessly Lost: [EMAIL PROTECTED] - help in body of message Brought to you courtesy of TLCHost.net http://www.tlchost.net/ ----------------------------------------------------------------------
