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Another 55v no xmit

C275 tests as a 11pf

Tr45 tests as a good transistor with 22 HFe.

R220 still tests as a 4.7 ohm.

R330 looks like it got hot on the bottom, coating is wrinkled.

Got to run pick up a laptop to upgrade, be back shortly.
 
I think he meant R222 (330ohm), which would take over 9v across it to produce the rated quarter watt (if it is a quarter watt resistor). Somethings definitely bad in that area!
 
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My bad, I meant R222 which is a 330 ohm. I replaced R222 previously with a new one, now it looks like heat got to the bottom of R222.
 
Cable Guy said:
Ok, you nailed it Brandon. That divider was over biasing that transistor, turning it on hard and burning the emitter resistor, right?
Click to expand...
Im thinking so. With 2.2v at the base, I would expect 1.5v at the emitter. 1.5v/4.7ohm=.319A or .478watt. If the base were 1.44v as the divider suggests, there would be .74v at the emitter, and .74v/4.7ohm=.157A or .117w. If the emitter resistor is a quarter watt resistor, it burning up is easily explained by the wrong base voltage.

The mystery is why R222 looks burnt if it was just replaced, because it would take the full 8v rail to heat a 330ohm resistor.

Gotta go to work, be back in a bit
 
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brandon7861 said:
The mystery is why R222 looks burnt if it was just replaced, because it would take the full 8v rail to heat a 330ohm resistor.
Click to expand...
That has me stumped. Assuming the 1.5k was shorted, that's .024A / .193 Watt across the 330 and if he used 1/8 watt that would burn up in time. Also, the base would have seen 7.92 volts. But it didn't.

If the 1.5K changed to say 750, that would put out 2.44 volts to the base as close to what was seen, but the current through the 330 would have been .007A / .018 Watt and wouldn't have burned.
 
Ok, got back home...
Yanked out R221 and R222.

Checked both on the tester and then on the ohm meter.

R221 out of circuit tests as 1.50k ohm on the tester and 1.496k ohm on the ohm meter.

R222 out of circuit tests as 330 ohm in tester and 329.98 ohm on the ohm meter.

All the disc caps I removed test as good in tester and around the same on the capacitor meter.
 
Curious thing is, C172 (104j, mica cap, large shiny) suppose to be 0.1uf 50wv but tests as a 92nf.
From my understanding 0.1uf is 10nf, not 92nf.

Took one out of another radio (parts radio), checked it and it also tests as 95nf.

On both my tc1 tester and my capacitor meter.

I test them twice on the tester and always come up with 9?nf...
 
With tr45 removed, what are the voltages on those pads, particular the base pad. Only thing I can come up with is a short somewhere on the traces, a leak in the transistor or a coupling or feedback cap went resistive.
 
Hawkeye351 said:
Curious thing is, C172 (104j, mica cap, large shiny) suppose to be 0.1uf 50wv but tests as a 92nf.
From my understanding 0.1uf is 10nf, not 92nf.

Took one out of another radio (parts radio), checked it and it also tests as 95nf.

On both my tc1 tester and my capacitor meter.

I test them twice on the tester and always come up with 9?nf...
Click to expand...
A 104 is 100,000 pf, or 100nf, or .1uf.
 
Ok, be back shortly.

Thinking the TR45 may be bad.
According to the datasheet, the minimum HFe is 10, typical is 80 and maximum is 300. This tr45 shows as 22, which is well below the typical range, closer to the minimum range.

Gonna throw these resistors back in, be back shortly.
 
Got all resistors and disc caps back in. Checked over thoroughly for any shorts/solder balls, all clear.

TR45 Solder pads with TR45 removed. Checked in transmit mode.
Base - 0.50v
Collector - 8.29v
Emitter - 2.06v
 

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