TRX2A L4 blowed

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Re: TRX2A L4 blowed

Postby 5B4AIY » 15 Oct 2016 06:05

Hi, Erich,

OK, that explains your symptoms. Note that R11/R12 and R23/R24 are 0.22 Ohms each, so that their parallel combination is 0.11 Ohms. They provide a small amount of DC negative feedback, but their primary function is that of providing a means of measuring the currents through the driver and PA stages.

With a combined resistance of 0.11 ohms, the voltage across the resistors is 0.11V/A. This is fed to a non-inverting DC amplifier formed by A1-A, with a loop gain set at +11, giving an output of 1.21V/A.

Whilst you have the PA board out, you might want to make the recommended modification to the pre-amplifier, TR1. There are two 'vacant' pads in the emitter circuit labelled C2 and R5. Revision A4 adds C2, 100nF, and R5, 10 ohms to increase the AC gain of this stage. When you have made this modification, you will need to reset both the CW and SSB drive levels.

If I can be of any further help, let me know.

73, Adrian, 5B4AIY
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Re: TRX2A L4 blowed

Postby HB9FIH » 14 Jun 2017 21:02

Now more than 6 months later, I am here again in QTH TA3 with replacemets.
Mounted:
- new R11/R12 (0R22)
- new TR2/TR3 (IRFR110)
- R6/R9/R15/R18 to 0 - tested all over C5/C7/C12/C14 (1-3 Ohms)
Started very slowly (yes) to turn R6 clockwise and watched for the current.
-- nothing to see for abt. 5 turns
-- suddently small smog - and fuse (I took an 1 Amp) blown.
-- checked - the (new) L4 was reason for smoke.....
- unsoldered the TR2/TR3 and checked -- both seems ok - like the last new one.

Now I am a bit helpless. Either spend a lot of time and then recognizing that I am missing new parts (not able to get them here in TA3). Or take the TX with me back to HB9 and find anybody who is willing to repair them for me.

I still have some replacement parts:
4 IRFI510G
1 T3 (Würth)
3 L1/L4/L7
8 0R22

de Erich :cry:

Next day 15.6.2017:

I have dreamed about TRX2.....
so I studied why it could this happend again (burning L4).
Because I can not see any increasing the current in the display (in my display the current is shown without the label "ID" - it's ok ??). (its the position after the Voltage which shows 13.8)
Could it be that there is something wrong with the Drain current detector ? - next I will check this.
(I already removed the T2/T2 again)
-- OK following checked:
ID Select J7-2 supplied with 0.1-0.3 Volts
after Output A1-A D%-R54 -> ID shows played Volts
then C25 Voltage checked -> OK same as ID.
C25 supplied with 0.4V -> Display 0.00 A
vy 73 de
HB9FIH
HS0ZLS
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