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Author Topic: Drake TR-7 and MFJ 969 bad vibes.  (Read 7009 times)
KG6YSF
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Posts: 91




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« on: October 04, 2012, 08:15:06 PM »

Hello all I am new here and this is my first post. I have a Drake TR-7 that I am just getting set up with a multi band dipole. I am useing a MFJ 969 tuner and not getting good results. As i try to tune into the dummy load the radio is shutting down. I cant get a good tune before the radio drops out. I believe and hope, that this is a self protection mode kicking in. Any help and or info would be apreciated.
I don't know how to adjust the power out on the radio. I was told that it does this automaticly by reading the swr. The higher the swr the less output. I hope this is right because the last time I tried to tune, the radio and lights dropped out and I have nothing. The fan powers up but the radio don't.  
« Last Edit: October 04, 2012, 08:35:13 PM by KG6YSF » Logged

"Rangers Lead The Way!"  "Sua Sponte"   "Litalis Velox Silens"
When all else fails ham radio is there!
FT2900, FT8900, VX6, Ft60, TS940SAT, Drake TR7, MFJ 969
AC5UP
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« Reply #1 on: October 04, 2012, 09:01:15 PM »

The Drake TR-7 is a broadband solid state transceiver. Assuming a non-reactive 50 Ohm load (like a dummy load) is connected directly to the radio there is nothing to 'tune'. The radio should give you ~ 120 Watts output (depending on the band) in CW mode. Power will be highest on the lower bands.

If the transmitter is shutting down there are two possibilities: The SWR foldback circuit is reducing the output power because the antenna load isn't what the radio expected - or - the power supply is shutting down under load. I suspect the power supply isn't able to supply enough current under load, but it's also possible there's a problem in the TX output section causing a false SWR foldback. The radio can draw as much as 25 amps in TX and many 13.8 volt "25 Amp" power supplies are more like 16 amp continuous, 25 amp surge. Be sure to check the supply voltage under load at the radio as the power cable may have excessive resistance and is part of the problem.

User manual is here: http://www.wb4hfn.com/DRAKE/DrakeManuals/TR7/Manual_TR7.htm
Schematic here: http://www.wb4hfn.com/DRAKE/DrakeManual-PDF.htm

Drake web page here: http://www.wb4hfn.com/DRAKE/DrakePageHome.htm

Since you are "new to all of this" your first assignment will be to RTFB and learn as much as you can about the radio before you break something. No Kidding. The TR-7 is a nice rig and you'll deserve eternal ridicule if you turn it into a doorstop.

PS:  If you don't know what " RTFB " means, better to find out the easy way...... Not the hard way.   Wink
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W8JI
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« Reply #2 on: October 05, 2012, 03:34:14 AM »

Hello all I am new here and this is my first post. I have a Drake TR-7 that I am just getting set up with a multi band dipole. I am useing a MFJ 969 tuner and not getting good results. As i try to tune into the dummy load the radio is shutting down. I cant get a good tune before the radio drops out. I believe and hope, that this is a self protection mode kicking in. Any help and or info would be apreciated.
I don't know how to adjust the power out on the radio. I was told that it does this automaticly by reading the swr. The higher the swr the less output. I hope this is right because the last time I tried to tune, the radio and lights dropped out and I have nothing. The fan powers up but the radio don't.  
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AA4PB
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« Reply #3 on: October 05, 2012, 05:52:09 AM »

The SWR foldback ciruits in most transmitters are intended to protect your transmitter from an occassional mistake of keying the radio into a mismatched (high SWR) load. They do this by reducing the power output when the SWR is high. They are NOT intended to be an "automatic power control" that allows you to routinely operate into a high SWR load.

On the TR-7, the "carrier" control can be used to manually reduce the power output in AM mode and possibly CW mode. I would connect the 50 Ohm dummy load directly to the radio and determine where to set the carrier control to produce about 10-15 watts output. Then connect the tuner and antenna and use that low power level to set the tuner for minimum SWR. After the tuner has been adjusted you can go back to full power output.

If the fan runs but nothing else (no Rx, no Tx, no lights) then you may have blown a fuse inside the TR-7.
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W8JI
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« Reply #4 on: October 05, 2012, 07:51:06 AM »

Pardon my last post. eHam does some freaky things sometimes, and I cannot figure out why. It told me I double posted, and it sent half a message.

Hello all I am new here and this is my first post. I have a Drake TR-7 that I am just getting set up with a multi band dipole. I am useing a MFJ 969 tuner and not getting good results. As i try to tune into the dummy load the radio is shutting down. I cant get a good tune before the radio drops out. I believe and hope, that this is a self protection mode kicking in. Any help and or info would be apreciated.

I had a TR7, and we used one on the test bench at Ameritron for a short period of time. We had to stop using it because it was difficult to keep final in.

That's a terrible way to tune. The TR7 is an old rig, it has sensitive transistors, and it has a pretty poor protection system.


Quote
I don't know how to adjust the power out on the radio.


You better read the manuals. As I recall, the "carrier" knob adjusts tune power. NEVER tune a tuner with the radio wide open.

Quote
I was told that it does this automatically by reading the swr. The higher the swr the less output. I hope this is right because the last time I tried to tune, the radio and lights dropped out and I have nothing. The fan powers up but the radio don't. 


Well, that isn't a good sign. Unless you blew a fuse, you may have damaged the radio. Whoever told you it was OK to depend on the SWR fold-back gave you terrible advice. You should never do that when adjusting a tuner with any radio.

More modern radios are generally safe so far as radio damage goes, but it is very difficulty to adjust a tuner while the radio is shutting down for SWR. It is far easier to adjust the tuner with the radio barely turned up, as described in most tuner manuals.

The TR7 is very old, did not have that good of a protection circuit to start with, and is easily damaged when operated into wild load impedances. Most modern radios, except Ten Tec's,  will tolerate repeated operation into nasty loads. The Drake radios, like many other early radios, will not.  We blew finals in the TR5 and TR7 at Ameritron so often we stopped using them on the test benches, and changed to Kenwood TS 440's.

You just can't run an old radio like that into wild uncontrolled load impedances and expect to not have problems.

73 Tom

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KG6YSF
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« Reply #5 on: October 05, 2012, 12:26:58 PM »

So assuming it will fire, I haven't tried yet this morning, run it on AM use the carrier to adjust power out and start again.
I am and have been tuning into the built in 300w dummy load in the tunner. On the cross needle meter both needles shoot strait up. Using the roller inductor, the antenna impedence controle and the transmitter impedence controle barely moves the needles. the "power in" setting on the tuner is at 300w. Huh
I had run the radio for a while on a dipole fan aray that I built and was working 80m, 40m, 20m, and 15m pretty well. I decided that I wanted the full HF spectrum, minus 160m, and swithed to a tuner, the MFJ 969, and a "mystery antenna" that my club has used for the last 6 years or so with an LDG Z11 and a TS440 very succesfuly on field days. I don't have the antenna hooked up yet and was hopeing to learn how to use the tuner while I waited to be able to get the final conector that I needed to finish the coax for the antenna. I hope that my exuberance din't bite me in the butt. Sad
 
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"Rangers Lead The Way!"  "Sua Sponte"   "Litalis Velox Silens"
When all else fails ham radio is there!
FT2900, FT8900, VX6, Ft60, TS940SAT, Drake TR7, MFJ 969
K8AC
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Posts: 1466




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« Reply #6 on: October 05, 2012, 06:39:59 PM »

I'll give you some info on the TR7, but I suggest you go to the Drake Yahoo group where you'll get detailed help in getting it straightened out.  First of all, stop screwing around with AM mode.  Use CW mode for tuning your tuner.  The output power is controlled by the Carrier pot on the front panel and you should be able to adjust the power output from ZERO to full power over the range of that pot. For full output, run the Carrier pot clockwise until the ALC LED just comes on.   A TR7 that hasn't been properly pampered can be a real pain to keep running properly and there are a number of possible causes for the loss of power problem.  For example, the power switch on the front panel AF pot is a major point of failure for power loss and most TR7s fail there eventually.  There's an overcurrent adjustment in the power supply that may be misadjusted causing the supply to cut out before the desired current point is reached.  If the TR7 is working properly, you should be able to close the key in CW mode with at least 50W out and run for hours that way.  But, unless a knowledgeable person has worked on it recently, I can guarantee you that it is NOT working properly.  None of the contact pins for the cards are plated with anything that resists oxidation and the first thing to do with any TR7 is to pull the cards one at a time and use De-Oxit on all the card pins.  Your TR7 has been around since the late 1970s and who knows how many "golden screwdrivers" have been used on it over the years.  Any and all adjustments could have been messed up over that time.  And - it may well be that the finals are gone, or, were replaced at some point and the job not properly done (and the original finals haven't been available for many years.  It sounds as if you don't have a separate dummy load, so you might just try connecting a 100W incandescent bulb as a dummy and see if you're getting any output that way.  The TR7 will be able to fully illuminate a 100W bulb without cutting back the output power, but then, a mis-adjusted SWR circuit in  the TR7 could prevent that.

73 and good luck - Floyd , K8AC

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KG6YSF
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« Reply #7 on: October 05, 2012, 10:30:47 PM »

Thanks all. I have my brother coming out to help me. He is an RF engineer and ba ham so he thinks he can help explain a few things and do a few tests.

I do not own a cw key. The way I understand it a key is nothing more than a switch that creates a short, correct?
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"Rangers Lead The Way!"  "Sua Sponte"   "Litalis Velox Silens"
When all else fails ham radio is there!
FT2900, FT8900, VX6, Ft60, TS940SAT, Drake TR7, MFJ 969
KG6YSF
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Posts: 91




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« Reply #8 on: October 12, 2012, 10:31:03 AM »

Brother hasn't been able to get away from work long enough to come out and help. So does any body know how to read the output of the PS7 power suply with a multi meter? ie. which pins to test from on the cable to the radio
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"Rangers Lead The Way!"  "Sua Sponte"   "Litalis Velox Silens"
When all else fails ham radio is there!
FT2900, FT8900, VX6, Ft60, TS940SAT, Drake TR7, MFJ 969
ZL1BBW
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Posts: 371




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« Reply #9 on: October 12, 2012, 12:39:31 PM »

So assuming it will fire, I haven't tried yet this morning, run it on AM use the carrier to adjust power out and start again.
I am and have been tuning into the built in 300w dummy load in the tunner. On the cross needle meter both needles shoot strait up. Using the roller inductor, the antenna impedence controle and the transmitter impedence controle barely moves the needles. the "power in" setting on the tuner is at 300w.

I would be surprised if the ATU part is even in circuit if its using the internal dummy load, pretty poor dummy load if it needs an ATU to tune it.

Silly thought, have you worked backwards from the tx input on the atu when its witched to dummy load and checked that you have 50 ohms all the way back tot he tx coax connector?.
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ex MN Radio Officer, Portishead Radio GKA, BT Radio Amateur Morse Tester.  Licensed as G3YCP ZL1DAB, now taken over my father (sk) call as ZL1BBW.
KG6YSF
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Posts: 91




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« Reply #10 on: October 12, 2012, 07:09:34 PM »

Silly thought, have you worked backwards from the tx input on the atu when its witched to dummy load and checked that you have 50 ohms all the way back tot he tx coax connector?.
[/quote]

Embaressingly I don't know how to do that. I was able to pass the general exam but don't know electronics.
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"Rangers Lead The Way!"  "Sua Sponte"   "Litalis Velox Silens"
When all else fails ham radio is there!
FT2900, FT8900, VX6, Ft60, TS940SAT, Drake TR7, MFJ 969
AC5UP
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Posts: 3845




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« Reply #11 on: October 12, 2012, 08:34:07 PM »

Set the tuner to the switch settings you used to select the internal dummy load.

Disconnect the tuner's jumper from the coax jack on the back of the Drake. Use an ohmmeter to measure the resistance across the coax jumper. One probe to the center pin, the other to the outer shield. At this point you should be measuring the resistance the dummy load in the tuner presents to the radio.

It should be very near 50 Ohms.

If it isn't, consult the documentation for the tuner to figure out why........ The Drake wants to see a purely resistive 50 Ohm load.
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KG6YSF
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Posts: 91




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« Reply #12 on: October 13, 2012, 12:50:08 AM »

That I can do. Thank you sir.
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"Rangers Lead The Way!"  "Sua Sponte"   "Litalis Velox Silens"
When all else fails ham radio is there!
FT2900, FT8900, VX6, Ft60, TS940SAT, Drake TR7, MFJ 969
WB6BYU
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Posts: 13172




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« Reply #13 on: October 15, 2012, 11:10:11 AM »

Some tuners can be set to feed the dummy load though the tuner - if that is the case
with your tuner, make sure it is in THROUGH or BYPASS mode.

Read the manual to understand how to adjust the output power using the CARRIER
control.  It's bad practice to adjust your tuner at full output power:  I used to blow
fuses in my TS-430 trying to do this.  Instead, turn the CARRIER control fully counter-
clockwise (minimum output power), set the meter in the tuner to the lowest output
power range, put the radio in CW mode, key the rig (any sort of a switch will work for
a key in this case) and slowly increase the CARRIER control (clockwise) until you
get a usable indication on the meter.  It doesn't need to be full scale, you just need
enough reflected power that you can tell whether the adjustments are increasing or
decreasing the SWR.  My tuner has 30 and 300W scales, and I generally use 5 or 10
watts on the 30W scale to adjust the tuner.  This makes life MUCH easier on the rig,
power supply, tuner, and other hams using the bands.

It does take some practice to get a feel for how to adjust the tuner.  You can try
it on line using W9CF tuner simulator here:

http://fermi.la.asu.edu/w9cf/tuner/tuner.html

Try putting different values in the boxes in the upper right-hand corner and adjusting
the tuner for a match.  The best method that I've found is to put both capacitors to
maximum and adjust the coil for loudest background noise on the band.  (This doesn't
work on the simulator, of course.)  Then  vary one or the other capacitor to see which
lowers the SWR the most, and adjust that one alternately with the inductor until you
get to a minimum.  In the process, as you get the sense of which direction one control
is turning it actually helps to go a bit past the minimum before adjusting the next one -
this reduces the number of back-and-forth steps required to get a good match.

Once you've tried it on the simulator, put the dummy load on your tuner and practice
matching it on different bands (using low power output from the transmitter, NOT
full power.)  When you feel comfortable with that, you're ready to try the antenna.
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KG6YSF
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Posts: 91




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« Reply #14 on: October 25, 2012, 05:05:47 PM »

Well the problems continue. It was recomended to me that I should check the pots in the power supply. I turned each of the two pots through a full range of motion in each direction and then returned them to their origional position. From there I was to actualy try adjustment. Well when I keyed the radio I no longer have ANY deflection on the meter at all. So I guess I am needing to know if I should go further by cleaning to see if the contacts became fouled after running them around. If so what parts should I be leary of if any, ie. do any hold a charge that I should be cautios of? Can I use contact cleaner spray or will it damage printed circuit boards or other parts? It needs a heavy cleaning. I have already vacumed and then blown it off with compressed air, yes my compresor has an air dryer. Alcohol should work, shouldn't it?
Once clean how should I measure the output voltage and amperage? I'v been trying to get an HF station set up and working on 10-80 for a year. I have had 80, 40, 20 and 15 working for a while on a fan di-pole array. I should have been happy with that but of course I couldn't be and so I opened a can of worms. So far they have been ravenous and mischivious. Seriously though, I have run out of money so I can't get professional help or a new power supply. I also do not know enough to do this on my own. I need some direction please.   
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"Rangers Lead The Way!"  "Sua Sponte"   "Litalis Velox Silens"
When all else fails ham radio is there!
FT2900, FT8900, VX6, Ft60, TS940SAT, Drake TR7, MFJ 969
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