All - looks like i lost output power on SSB.

Here is trace of what happened.? By mistake i had wrong antenna plugged in.

1. I will test CW output to see if there is any power after PTT on mic PTT.
2. PTT relay is kicking in with SSB; i am able to hear modulation on receiver nearby.

Could Q90 be gone? or IRF510?

for Q90 - what is the exact component or is there a substitute i could use.

Appreciate your inputs.

Sajid Rahum,

There is a spreadsheet in the files section with voltages for the transistors.? Look for vu2zap in the files search.
/g/BITX20/files/VU2ZAP

The power sections of the different versions are the same, so the voltages should be correct or at least close.

73
Evan
AC9TU

开云体育

Finals are burned out ?you need to replace them happens to me with an handled yeasu ?check power out with wattmeter and you will find less then 200 mW

great man.? for Q90 - what is the component which if it is bad i need to source?

For changing IRF510 - just decouple the heat sink and desolder them and replace them back?

Thanks Evan
What is the Q90 component actual ic number?? I tried to google it but not able to get a firm ic value.? Even the schematic does not talk to it.

Sajid

Not sure if I should get a 2n3904 smd? or BFR106.

On Mon, Dec 20, 2021, at 01:36 PM, Sajid Rahum wrote:

What is the Q90 component actual ic number??

It is MMBT3904 which is the surface-mount version of the 2n3904.

I would not use the BFR106 in place of Q90.? I have not read of others replacing Q90 with anything other than another MMBT3904.? Replacing the 6 through-hole 2n3904s with 2n2222as after Q90 has been reported as improving the overall power difference across bands.

If you do need to replace the IRF510s you will need to do the bias adjustment as there is a difference between IRF510s.

73
Evan
AC9TU

"Replace Q90 with BFR106" per Allison's power chain improvement right-up.? Discussed and in the wiki.

Rgds,
Gary

On Tue, Dec 21, 2021, at 07:12 AM, Gary Anderson wrote:

"Replace Q90 with BFR106" per Allison's power chain improvement right-up.? Discussed and in the wiki.

Thank you Gary for the correction.? Would you by chance have the message number that refers to that discussion?? I would like to read through it to see what I missed.

73
Evan
AC9TU

Evan

You are still active on this forum
i think is't here

[email protected] | Wiki

cdt

Gary,

An update on the BFR106 replacement.

I did a search on the server and found a number of hits with regard to replacing Q90 with a BFR106.? The results that I see are not really spectacular and do require changing the bias to fall within the specifications of the transistor.

If you are going to replace Q90 with a BFR106 you also need to adjust R81 to get to the 10ma level that is the correct bias for that transistor (as I understand it).? ?For the modest gains, I would stick with the MMBT3904.? Changing out the 6 following leaded 2n3904 with 2n2222a mounted on the bottom of the board has been reported as improving the overall performance.? There is a recommendation to adjust that bias as well, though good results have been reported with just the transistors swap.?

Here is one of the messages on the BFR106 in Q90:
/g/BITX20/message/67333

Here is the link to comments on Allison's findings:


If my memory serves me correctly, at some point Allison stopped work on flattening the power of the uBitx when the signal purity came under scrutiny.? This was prior to the v5 and v6 that do not have the purity issues.? I am not sure what work has been done since then other than changing the values of R83 and C81.? These changes were to address the "40meter Dip" that is caused by impedance mismatch at the base of Q90 to the LPF and the first mixer.

Also, the intent of the effort was to flatten the response, giving up power on the lower bands for power on the upper bands.? If you go into the table of power values you will see that.

Unfortunately, there is not a single source to go to to find the best solution for you.? Part of the fun is the "mining" for the information to then use to solve your need.

FWIW
73
Evan
AC9TU

Gerard,

I read almost all of the posts.? Others are offering the same advice that I would, or I do not have an answer so most of the time there is no new information to add.? For this thread, I did not see a post, so I chimed in, though it might have been better if I waited for others to respond.

thank you for the link.? I will need to bookmark that now.

73
Evan
AC9TU

I replaced the IRF510s - still no luck.? Nothing is outputting.? I just hear a humm on the speaker.

Sajid Rahum,

First off, were you able to do the bias adjustment?? Then if that worked as it should, did you do the voltage checks in the spreadsheet from Raj, vu2zap?? You only need to focus on Q90, Q92 to Q97, Q911, and Q912 until you get a CW signal out.? After CW is working then you can look into SSB issues. Remember that the spreadsheet voltages are in SSB mode with the PTT pressed and no sound in the mic.

If the static voltage checks pan out then you will need to do the RF probing to see where the RF is being lost.

Hope you find the issue.
73
Evan
AC9TU

Farhan

Unfortunately, i dont have an osciloscope i will need to get an RF Probe made up or order a simple oscilloscope.

I had put a wrong antenna. By the time i realised it was late after pushing a few ptt calls.

Symptoms I am gettings:
1. When? I switch on, audio control is no longer function - it is at full capacity out of the speaker - as though the knob has no use.
2. When I PTT - I just get a loud humm in the speaker - no output being detected on power meter.

I did change the IRF510 - I dont think issue is there.

Hi Evan

I did not try CW - i dont have a key wired.? I could try to put a basic contact switch to function as a key.

Sajid

Sajid Rahum,

What did the transistor voltage checks show for Q90 to Q912 (just the power amp transistors)?

73
Evan
AC9TU

On Wed, Dec 22, 2021 at 12:20 PM, Sajid Rahum wrote:

I did not try CW - i dont have a key wired.

Put it in CW mode and press the PTT switch on the microphone.? That keys the transmitter in the CW mode.

depending upon which firmware he has installed - he may not have a CW mode.? so PTT may not give CW if he is using stock firmware.? any short circuit across the KEY jack will produce CW - you could even wire up a switch here.?

I am thinking for Q90 use whatever NPN is on hand - 2n3904, 2n2222 etc - leaded form is fine.? objective now is to restore this OM's rig not improve it.?

see if you can follow Ashhar and Evan's troubleshooting advice.? I am hopeful the damage is minimal and inexpensive available parts.?

73 Curt wb8yyy