Texas star dx 350 staying hot when off?

[DoctorAudio]

Yeah..

 

[Ranch55]

Well, nomad is right, if the amplifier heat sink is getting / staying hot, then that means the heat is being generated by the RF power transistors.
It would be prudent to check the transistors bias resistance first, then do a quick check of the transistors bias voltage.

 

[SuperLid]

Self oscillation?

 

[linearone]

Self oscillation?

It's never oscillation. It's always a broken bias circuit or bad pills

 

[Ranch55]

Check the bias resistance of the transistors first.
Of course, with all DC power removed/unplugged from amplifier.

 

[nomadradio]

A Texas Star won't oscillate without base current to the RF transistors.

73

 

[rflegacy]

I replaced Q1, Q2, C18 and C19 with no luck. Amp still getting hotter then hell.

 

[linearone]

I replaced Q1, Q2, C18 and C19 with no luck. Amp still getting hotter then hell.

Disconnect the bias choke going to the bases. See what happens. Does it have bias? Have you checked?

 

[DoctorAudio]

He mentioned that the meter light goes out when it's unkeyed. Being as the light gets voltage from the same switched source as the bias supply, I doubt the bias supply is staying on.

 

[nomadradio]

I doubt the bias supply is staying on.

But something is.

Simply lifting the base lead of all four transistors from the foil pad should stop the renegade current drain.

If it doesn't, there's one or more failed transistors.

If this DOES shut down the renegade receive current, next measurement to make is the voltage to ground at each of the foil pads where a transistor base lead was lifted away. Should be zero. If not, it's coming from somewhere.

Troubleshooting any kind of short circuit consists of taking things loose until the fault current is interrupted.

73

 

[SuperLid]

Why not simply determine what is heating when off? What component(s) are HOT to the touch or thermometer?

 

[Shadetree Mechanic]

Checking bias.

 

[nomadradio]

What component(s) are HOT to the touch or thermometer?

Seems to me he said the heat sink gets hot. Only the RF power transistors will raise the temperature of the heat sink.

73

 

[SuperLid]

Seems to me he said the heat sink gets hot. Only the RF power transistors will raise the temperature of the heat sink.

73

I have seen bias resistors attached to heat sinks with compound.

 

[Ranch55]

Check the bias resistance first .........
Then check the bias voltage.........very quickly.......
These are the two easiest things to do FIRST without changing out components and guessing.......