Bad transmitter or PA in a Maxtrac 300?

[karlschneider]

I tried to find anything on this but didn't...sorry if it has been covered!

I'm new to Batlabs and also to modern Moto radios having been out of the hobby for many years, I built what I think was the first 2M repeater west of the Miss river back in ~62 on my mom's back porch using a scavanged 1/4KW transmitter, a 5V receiver with homebrew squelch relay...a real kludge but it did work and it's still on the air having had several reincarnations of hardware & ownership (It's WA5LVT in Tulsa)...anyway I'm semi-retired and doing some radio playing again.
So I have this Maxtrac 300 I scared up that receives great, programs properly but won't transmit...it -tries- to but cuts on and off about 2 or 3 times a second. I can see about half a watt on the Bird but there's no VHF signal. The nearly counter shows various freq's around 5 MHZ not steady, so I'm assuming the PA is bad but I am wondering if there is ANY chance there's something in the codeplug that I've farkled.

(The Max is a 146-174 45W 16 Ch radio...I don't believe I have a power supply problem 'cause the same one runs a Radius M216 just fine.) So anybody have any suggestions or encouragement?
73

on edit: I should have mentioned, I found it had been set up for ignition control and external speaker (the internal speaker was not even connected...I hooked that up and jumpered 12V to the 5 pin connector to get it powered up & getting audio), so it has struck me to wonder, is there anything in the external cabling that would cause this behavior on the
Xmtr?

thanks

[Jim202]

You might try looking around the TX VCO area. it kind of sounds like the TX may try to come up and then the VCO goes out of lock. I would expect you to get an error tone when this happens.

The other area is the power supply feed in the PA. It could be loosing the DC power to the final transistor. You might want to open up the PA cover and poke around in there. Has been some time since I looked at the PA wiring diagram. Might even be some problem with the power control circuit.

Jim

So I have this Maxtrac 300 I scared up that receives great, programs properly but won't transmit...it -tries- to but cuts on and off about 2 or 3 times a second.

thanks

[Max-trac]

Does it do anything differently when you go into the Service transmitter alignment section with RSS and attempt to tx using the F6 key?

[karlschneider]

[quote="Jim202"]You might try looking around the TX VCO area. it kind of sounds like the TX may try to come up and then the VCO goes out of lock. I would expect you to get an error tone when this happens.

The other area is the power supply feed in the PA. It could be loosing the DC power to the final transistor. You might want to open up the PA cover and poke around in there. Has been some time since I looked at the PA wiring diagram. Might even be some problem with the power control circuit.

Jim



[quote="karlschneider"]
So I have this Maxtrac 300 I scared up that receives great, programs properly but won't transmit...it -tries- to but cuts on and off about 2 or 3 times a second.

thanks[/quote][/quote]


I'll look into that, thanks! I need to learn how to use this message board better...meanwhile thanks for the tips.

[karlschneider]

[quote="Max-trac"]Does it do anything differently when you go into the Service transmitter alignment section with RSS and attempt to tx using the F6 key?[/quote]

I didn't think to try that. I will in a few minutes...thanks will let you know!
ks

[karlschneider]

[quote="Max-trac"]Does it do anything differently when you go into the Service transmitter alignment section with RSS and attempt to tx using the F6 key?[/quote]

AH! Update here...thanks to your suggestion, I discovered that I COULD key the XT from in the RSS. I cut back on the xmtr power to about 48% and it began working! So perhaps there IS a problem with my power supply, I'll have to investigate that. As of now the radio is actually working okay as far as I can tell. THANKS to everyone!

[jackhackett]

Quick message board lesson.. if you're going to quote in your reply, uncheck the 'Disable BBCode in this post' box.

[tvsjr]

Does it do anything differently when you go into the Service transmitter alignment section with RSS and attempt to tx using the F6 key?

AH! Update here...thanks to your suggestion, I discovered that I COULD key the XT from in the RSS. I cut back on the xmtr power to about 48% and it began working! So perhaps there IS a problem with my power supply, I'll have to investigate that. As of now the radio is actually working okay as far as I can tell. THANKS to everyone!

Stick your Bird on the radio and see what it looks like... could be foldback due to high SWR as well. Are you testing into a known-good dummy load?

Don't leave the power turned down on the Maxtracs... they get pretty inefficient and thus very hot if turned down too low, like most other M radios.

Also, the "48" you're seeing isn't 48pct... it's just a relative value (softpot). FYI.

[kb0nly]

Sounds like now you either need a higher current power supply, or your dummy load or antenna in use is presenting a high SWR to the radio. Or maybe a bad cable, etc.

For a 25w D33 model figure at least 9.5-10amps on transmit, a high power 45w D43 is 15amps or so on transmit.

[mike m]

Also check the emergency jumper on the rear connector and or the emergency programming in the RSS.

[W6JK]

I built what I think was the first 2M repeater west of the Miss river back in ~62...

There's at least some competition for that claim:

http://wa6tdd.tripod.com/

'JK