Motorola Astro Spectra High Power W3 Shuts off on PTT

[dklortie]

Hi All,
First of all let me thank all of those who share their knowledge with everyone.

I am having an issue that I am hoping someone has seen before, and can help me solve.

I have a Motorola Astro Spectra High Power with the W3 head VHF. The radio has been used mainly for 2 meter amateur use on analog and digital, as well as listening to local analog fire departments and a P25 trunked police force.

A while ago, the radio suddenly started acting funny. When I would key the radio to talk, it would immediately shut the radio off (no delay or warning just instant dead on PTT). I hadn't done a reprogram or anything except turn it on and off when I would get in and out of the truck. Also, there were no error codes on the screen at startup or when it would shut down. At first I though it was a power supply issue from my battery to the radio. That proved to be fine. I then brought the radio in the house and put it on my Astron 50amp supply, and still the same problem. Shuts off immediately upon pushing PTT.

Thinking it is a fuse issue, I checked all fuses inside and outside of the radio with all being fine. As I was tied up with other things I put the radio aside and am just now getting back into working on it.

I tried to put in the original code plug that was in the radio when I got it, and still acted the same. PTT -> radio shuts off.
I went into the Astro Radio Tuner program and read the radio. Going into the high power adjustment, I click on the PTT button (expecting it to shut the radio down), and it transmitted just fine. 106 watts going into the service monitor. So definitely not a power supply issue. Was showing about 23 amps on the power supply. Same results on the middle and low power with obviously lower current draw.

Scratching my head, I moved each soft pot for power down 1 level and programmed into the radio. Rechecked the PTT on the mic and instant shut down.
I also checked the Oscillator alignment and was -15hz. Pretty close I'd say.

I by accident when going to turn the radio back on with the left button on the top of the HHCH, I pressed the PTT and the radio came to life. I then shut the radio off, and held the PTT down, allowing the radio to start up while holding the PTT down. Radio started transmitting fine at proper power output. Release the PTT and press again, and radio shuts off. WHAT?? It was just transmitting~!

I then turned the radio back on and was just going to put it on the back shelf for now and use it as a very heavy scanner. As I went to leave the room for the night, I started to disconnect the radio, forgetting that it was still on. I pulled the main power cord out of the radio, and all of a sudden heard the local fire department getting dispatched out. WHAT???? Power cord is in my hand. The only thing that was still connected was the ignition wire + and the coax, which I am assuming was keeping the radio alive.

So long story short, I am at a loss as to why the radio would shut off. It is obviously not a bad PA as it puts out full power when using the tuner software and when starting the radio up with the ptt held. When the radio is turned on the normal way, shuts off as soon as the PTT is pushed.

Is there something that I have missed? Really like the radio, but would like it even more if it would transmit and not just receive.

 

[DPapay]

Spectra's and astro spectra's have an issue, that /\/\ even had a service bulletin on. They would reset, immediately after the ptt was pressed. They, the techs, discovered that in certain set ups, rf would get into the control cable, causing this. We have had luck in the past by adding ferrites, to both ends of the control cable to correct this issue. It seems the chassis side usually was the culprit, but we still put them on both sides. You just clip them onto the cable.
Here is a link, I did not look closely at the wire size, but this type of ferrite is what you would get.

Amazon.com: Noise Filter Cable Ring, VSKEY [10pcs 7.0mm] Anti-interference Noise Filters Ferrite Core Choke Clip For Telephones,Tvs,Speakers,Video,Radio,Audio Equipment & Appliances Power Audio (7.0mm)

Amazon.com: Noise Filter Cable Ring, VSKEY [10pcs 7.0mm] Anti-interference Noise Filters Ferrite Core Choke Clip For Telephones,Tvs,Speakers,Video,Radio,Audio Equipment & Appliances Power Audio (7.0mm)

www.amazon.com

 

[wgbecks]

Great advise! Try connecting a decent dummy load directly to the antenna port without using any jumper cables, then retest to see if the radio still shuts down upon PTT.

 

[dklortie]

Hi Guys. Thanks DPapay and wgbekcs.
I tried both of your suggestions one at a time and no dice. As soon as I press the PTT the radio shuts off and I have to turn it back on again.
I watched the ammeter on the power supply and it just gives a quick bump (like a flash) to about 1/2 - 3/4 amp and then the radio shuts down.
I am going to open the radio and try putting a jumper from the main power connector to pin 3 on J5 to give it permanent ignition sense (something I kept meaning to do anyways), and then try plugging the HHCH directly into J5 and see what happens. Basically eliminate the Y cable and rule that out.
It is almost like the PA is not getting enough power and it is causing the radio to shut down. I have confirmed that I have all the voltages at the interface per the service manual, so I know that is not the case. Also it is running on a 50amp astron power supply in the shack at 13.9volts, so not under voltage.
Perhaps there is something else crow-baring it?
Will get back to you when I try plugging in the HHCH directly without the cable Sucks having this ignition sense wire required from the Y cable.
I have to run to the boat this evening also and will get the W3 head from the mid power radio I have on the boat and see if it is perhaps the HHCH?

 

[wgbecks]

Here are two quick tests and a couple of additional thoughts....

Have you tried turning down the power in CPS? Try running and one or more lower power settings to see if that has any impact on the shutdown condition.

Using Tuner, check the PA Bias settings per the instruction in the Basic Service Manual for your specific power and frequency range. Readjust as necessary and retest at full power outside of Tuner.

If the problems persists and neither of the above made any differences, then connect up a VOM at the cathode of CR-3840 on the PA board. This diode is there primarily to protect against reverse polarity but make a good test point to measure the A+ as it is applied directly to the
high current section of the PA. You should seen nominal supply voltage but will want to look for any significant drop in voltage when keying the transmitter that would be an indication of a there being something in the high current supply rail that's incapable of carry full PA current.

It the above test doesn't indicate a voltage drop problem then remove the supply and temporarily tack solder a short jumper wire across PA current shunt R-3849 and repower the radio and attempt to key the transmitter again. If the shunt resistance has gone out of tolerance then the voltage sample (replica of PA current) sent to the processor might signal a high PA current condition thus causing the shutdown condition.

There are only about a million possibilities that can cause this problem but these are two basic tests that I would perform if this radio was on my service bench. Now, don't quote me on this, but I want to think that the processor will mask (ignore) high current alarms when under control of Tuner and that might explain why you can obtain rated power in tuner without the unexpected shutdown.


Bill

 

[cmdrwill]

FIRST set one of the Modes to low power in CPS, rather than messing up the radios Alignment and Calibration values.
Then see if it keys up on that mode using a known good dummy load.
Also check for voltage drop in the power cable at the radio.

 

[dklortie]

Thank-you wgbecks and cmdrwill;
I have gone throught the alignment bringing the min power to 54 and max to 70. Also set the current limit and still no dice.
As for the low power setting, I cleared out the cps and put only 2 modes 146.52, one on high and one on low. Still does the same on both.
I am going to pull the lid and try Bill's instructions for the CR-3840 and R-3849.

Darren

 

[cmdrwill]

min power to 54 and max to 70.

Was that actual TX power or just the calibration number(s)"

 

[dklortie]

Hi cmdrwill. The 54 and 70 are the actual output power as shown on my service monitor. Off the top of my head, I don't remember what the soft pots are set at, just what I set the output power to having read that 50 was the minimum recommended power for these units..
I have done as Bill had suggested and checked the voltage at CR-3840. There is no chance to see if there is a voltage drop when keying the PTT, as even with an analog and digital capture meters, it shuts off so fast that the meter doesn't even have time to register. When I manually PTT through the tuner software, I loose about 0.3 volts as measured there at full output.
I have also tried as Bill mentioned and checked R-3849 by placing a short across it. Still made no difference.
Starting to think I may have a very heavy scanner on my hands here.
I am starting to wonder if there is something in the S-rec that may have gotten corrupted. May look for an replacement S-rec and throw that in and see what happens. Perhaps will fix, perhaps not?

 

[cmdrwill]

When I manually PTT through the tuner software, I loose about 0.3 volts as measured there at full output.

Best clue so far. Now is that on the bench or in the vehicle? And probably on a good dummy load?
I would NOT be screwing with the S- rec.

 

[dklortie]

This is in the shack, with an Astron 50 amp power supply. 13.8v measured at the terminals of the supply.
Leads to the radio are the stock power cord about 3 feet long, so virtually no voltage drop there.
When radio is unkeyed shows 13.8. When keyed up through tuner PTT at 100 watts, about 13.5-13.6 according to meter.
Radio is into a 50ohm 1kw dummy load that I have swept with the antenna analyzer and is 50ohm 1:1.

 

[wgbecks]

Sorry, I haven't kept up on your progress in testing. If you haven't done so, try connecting a car battery or other storage cell of adiquate
capacity in place of, or in parallel with your Astron power supply. I've seen issues with the voltage regulator in these power supplies
going south from RF getting into them.

Another suggestion is to use a fast storage scope to monitor the supply voltages and various test points to see if you can capture any
events prior to the shutdown including that supply from the Astron.

Bill

 

[cmdrwill]

This is in the shack, with an Astron 50 amp power supply. 13.8v measured at the terminals of the supply.

Another good clue. And this was on the test frequencies in the calibration alignment of the RSS?