Title: Low drive, 10 meters
Post by: WD8BXS on 22. September 2020, 17:53:14
I have one (mcHF) on the bench, and it has low drive on the upper bands.
It has similar signals at the output of T5 on all bands, but on the upper bands there is low output on the drivers Q3 and Q4.
I have tried new ones, but same result.
I have another radio here with the same type drivers and it does not show the same results, it has good driver out put on the upper bands.
Any ideas??
Tnx, Chuck |
Title: Re:Low drive, 10 meters
Post by: DF8OE on 23. September 2020, 04:55:45
Hi Chuck,
1) defective band pass filters (solderings, wrong parts)?
2) bad solderings at TX transformers in front or at output of band pass filters?
You can easily follow the signal path using an oscilloscope and TUNE function.
good luck - stay healthy - vy 73
Andreas |
Title: Re:Low drive, 10 meters
Post by: WD8BXS on 23. September 2020, 12:39:45
Hi Andreas,
Yes, that is what I am doing.
That is how I have arrived at these results.
I have good signals to driver input.
Low signal on driver output on 17 meters and up. |
Title: Re:Low drive, 10 meters
Post by: DF8OE on 23. September 2020, 14:11:52
If you got good input and no or low output there are only two possibilities:
1) driver transistors defective (both??)
2) load at outputs too high, mainly at high frequencies
3) wrong parts published (resistors and capacitors around drivers)
There are NO OTHER POSSIBILITIES. Or the input isn't good at least...
To check 2) desolder 100n coupling capacitors and check now.
vy 73
Andreas |
Title: Re:Low drive, 10 meters
Post by: WD8BXS on 23. September 2020, 16:31:17
Yes, I desoldered the 2 100nf and no change.
I will examine the other part values.
I have tried 2 new transistors, could all be bad??
Chuck |
Title: Re:Low drive, 10 meters
Post by: DF8OE on 23. September 2020, 16:45:58
If you got cloned ones: of course! What is the source of the transistors?
vy 73
Andreas |
Title: Re:Low drive, 10 meters
Post by: WD8BXS on 23. September 2020, 23:29:49
Title: Re:Low drive, 10 meters
Post by: DF8OE on 24. September 2020, 05:00:20
Mousers, Digikey, Farnell do not sell fakes. You have definitely one of the other mentioned issues. For bug hunting you need in optimum a spectrum analyzer (for looking what you are amplifying), an oscilloscope (signal amplitude checking), a DVM (checking DC states at drivers, checking BIAS of drivers), an inductor tester (or VNA) for checking health of collector inductors.
vy 73
Andreas |
Title: Re:Low drive, 10 meters
Post by: SP9BSL on 24. September 2020, 07:08:01
Hi,
I would suggest to check the collector coils, 47uH often has self resonance around 10MHz. Try to insert lower value coil for experiment, let's say 4.7uH and check if the higher bands signal level rise. |
Diskussions- und Newsboard des DARC-Ortsverbandes I40 | Powered by YaBB SE
© 2001-2003, YaBB SE Dev Team. All Rights Reserved.
|