A9 spectra goes nuts when it gets hot....suggestions?

[Elroy Jetson]

I'm GUESSING that the problem I'm experiencing is related to aged capacitors that need to be replaced.

My A9 VHF Spectra, (110 watt remote mount) goes nutty when it's been transmitting for a while and
gets hot enough that you wouldn't want to handle it. The receiver starts to flutter out on a signal
that it should be receiving, and then it stops unsquelching on any signal but it can be manually
unsquelched, and at that point you won't hear any received signal, just squelch noise. The transmitter
still works normally at this point, but of course, there's no longer any need to transmit with it in that
condition.

Letting it cool down enough restores it to normal operation

I'll probably replace every electrolytic cap in it, as they're due on age alone, but should a 110 watt
A9 get that hot? I doubt I'm hitting it any harder than it would be likely to have been hit when
in police service, and they're known to be all-day reliable for public safety use.

It seems to me that it should be able to run forever on a pretty heavy duty cycle, or it wouldn't
have been a popular radio in public safety, but this sucker gets hot enough that I'm a little bit
concerned about it.

I don't intend to drop the output power. The way I see it, if you have to drop it to a lesser value
than what it's rated for and advertised for, then you've got a problem that needs fixing, not
a weakness you need to make allowances for.

So what do you think? Anyone seen this sort of issue before, and found what's going on and how
to resolve it quickly and simply?

Elroy

[Will]

I have seen that, 1.) the thermal compound under the PA transistors goes bad, dries out. 2.) Bad caps.

Also it IS possible to overdrive the PA and it will get really H0T.

"Bad caps": there is a failure condition that will overdrive the finals on the PA. You can not control the power output. See if you can lower the TX power to some lower value, say 50 watts.

[Elroy Jetson]

So what would be the "normal" temperature range that the PA should not exceed under normal (but heavy) use?


And should I expect to see harmonics and/or spurs in the output if it's overdriving?

And, will they really do the full 110 watts normally? Or is that a best case scenario in the REAL world?


Elroy

[Will]

So what would be the "normal" temperature range that the PA should not exceed under normal (but heavy) use?

They do get hot but not over 140F

And should I expect to see harmonics and/or spurs in the output if it's overdriving?

Not usally do not show spurs or the like. Harmonics are filtered in the low pass filter.

And, will they really do the full 110 watts normally? Or is that a best case scenario in the REAL world?

You bet they will do more than 110 watts normally...


Elroy[/quote]

[George]

What are you doing? What kind of duty cycle are you trying to accomplish?

The Spectra was BARELY able to pass the 90 5 5 test for duty cycle and does NOT have the heat sink for anything beyond that. That's also part of the reason why they took so LONG to introduce the high power model when the 50 watt model had been out for some time and the 100 watt X9000 was still long in production. A Spectra is not an X9000 and not even a Maratrac and certainly not a Micor.

It sounds to me like you are hitting the thermal limits and you need to back it off. What is your timeout timer set for? Is this packet? Is this some kind of repeater? What is this?

George

[Elroy Jetson]

Ragchewing, with a 2 minute TOT that I've never hit yet.

The heatsinking DOES look a bit skimpy to me, at that.

I think it's going to get a fan mounted on it that runs all the time the radio's turned on, as part of what I will do to it,
when I get around to it.

The X9000 MAY be a better radio but the RSS for it is a real clunker.

Elroy

[Will]

The Spectra hi power/T83 is rated at the full 110 watts output with a one minute Tx and four minute RX, 20% duty cycle.

Elroy is going a little too far with a two minute time out timer. Should be set for ONE minute... and back off the PA to 80 watts, and no one will ever notice...

Over heating can also be caused by improper mounting in the mobile not allowing enough air circulation. Another hint.. put 1" spacers under the mounting plate for more air circulation arround the chassis. The Spacers are part of the instalation kit.

George, where did you get the 5-5-90 spec.??? (5-5-90 is a portable battery rating)
The Spectra hi power power amplifier is better than the Maratrac, Mitrek, and way better than the Micor.. And even tho it is a much better design than the Syntor X9000, the heatsinking is about the same. The Syntors have the same one minute TX and four minute RX rating as does all Spectras.

[Elroy Jetson]

I found part of the problem.


My shop's service monitor is DEFINITELY out of calibration when it comes to the wattmeter.


I checked output with a separate wattmeter that IS in calibration, and discovered the Spectra was pumping out 125 watts easy.

So I backed it down to 80 watts. That oughta help.

However...it's now at the "MUST GET HELP" stage. It got a little warm again, before I retuned it, and it hasn't recovered fully.

The receiver doesn't operate properly but it acts like a command board problem, instead. So it's time to recap it, NOW, I think.


Who has the recap kit for a T83 drawer unit? Or a list of the caps I'll need?

I have MOST of the Spectra manuals but not the T83 manuals.

I might have to just go searching in the radio and make a list but if someone here already is set up to do the job,
I'm interested. I only have so much time available to pursue so many different projects and I'd gladly pay a reasonable
fee for someone else to recap the drawer unit if they're set up to do it in a timely fashion.



Elroy

[Will]

..... if someone here already is set up to do the job,
I'm interested. I only have so much time available to pursue so many different projects and I'd gladly pay a reasonable
fee for someone else to recap the drawer unit if they're set up to do it in a timely fashion.

Elroy

Well, that is what I do best...repairing Spectras.

[Will]

snip>
The receiver doesn't operate properly but it acts like a command board problem, instead. So it's time to recap it, NOW, I think.

Elroy

I found some leaked capacitor dammage on the RF board, and a trace was eaten away. That did cause a Synth lock FAIL001.
I did find a problem in the receiver when the radio gets warm, but the problem is in the second IF stages on the RF board, not the Command board.