Author Topic: ft-901dm ham radio repair.  (Read 27944 times)

0 Members and 1 Guest are viewing this topic.

Offline drforbin

  • Regular Contributor
  • *
  • Posts: 97
Re: ft-901dm ham radio repair.
« Reply #125 on: December 17, 2015, 08:00:20 pm »
Thanxs for reply. I tried tuning it while in circuit it did nothing.
This was done before I removed it. As I showed with the lcr meter it seems bad.
It manual calls for 300 uH all I can get out of it is 5.6 uH.
The manual does say something about tuning the l09 but as you said the manuals are very unclear.
I find Alot of mistakes in the manual.
Sorry to hear about kiddie. I have two which are aLittle over 12 years right now.
 

Offline AF6LJ

  • Supporter
  • ****
  • Posts: 2900
  • Country: us
Re: ft-901dm ham radio repair.
« Reply #126 on: December 17, 2015, 09:03:49 pm »
Thanxs for reply. I tried tuning it while in circuit it did nothing.
This was done before I removed it. As I showed with the lcr meter it seems bad.
It manual calls for 300 uH all I can get out of it is 5.6 uH.
The manual does say something about tuning the l09 but as you said the manuals are very unclear.
I find Alot of mistakes in the manual.
Sorry to hear about kiddie. I have two which are aLittle over 12 years right now.

Double check the listing in the manual, make sure you have the right part.

Sue AF6LJ
Test Equipment Addict, And Proud Of It.
 

Offline drforbin

  • Regular Contributor
  • *
  • Posts: 97
Re: ft-901dm ham radio repair.
« Reply #127 on: December 17, 2015, 09:08:28 pm »
I have triple checked it. It's l09 main chassis. I have a very good LCR and as I said i'm getting about 5.4 uH on it.
 

Offline voltz

  • Frequent Contributor
  • **
  • Posts: 266
  • Country: gb
Re: ft-901dm ham radio repair.
« Reply #128 on: December 17, 2015, 10:17:52 pm »
Hi all,
Been looking at the diagram again and it looks like L09 is actually just a preselector extender for the 160 and 80m bands. If you look at wafer S1-J (i think it is) this coil is shorted out for all bands except 160 and 80. Its just allowing the preselect coil to cover these bands more easily and improve the position on the dial.
The other thing is, and if anyone is interested, the FT101ZD which has a very similar PA circuit does not have any coil like this in it. I guess when they did the 901 later, they extended the range of the preselect using this coil.
My guess is, there is no real adjustment to do with it, other than make sure 160 and 80 are covered on the preselect dial. I think!

Like i said before, your very fine LCR meter (which it is) may not be able to accurately measure inductance of dust iron RF coils. RF coils should be tested at RF, not audio like 1khz.. Its a different world and my theory in advanced magnetics is limited... Maybe the manual value is even a mistake. Either way, simply short it out and rule it out. Just like the 101 does.

Take care everyone.

Sorry for your loss AF6LJ, i know what its like, like loosing family isnt it.. Had so many pets over the years.. Now these four are a real handful, around 10 months old and a mother cat :)
 

Offline drforbin

  • Regular Contributor
  • *
  • Posts: 97
Re: ft-901dm ham radio repair.
« Reply #129 on: December 17, 2015, 10:43:58 pm »
You have four kiddies? Great. I agree maybe the meter is not working at high freqs.
But it does measure the other values accurately. I will short it and see what it does.
 

Offline drforbin

  • Regular Contributor
  • *
  • Posts: 97
Re: ft-901dm ham radio repair.
« Reply #130 on: December 17, 2015, 10:49:51 pm »
I remember when I was in England last (during the 90's) what impressed me is how many shops you could walk into and there was a cat or dog roaming about!

Could you send pictures of kiddies?
 

Offline voltz

  • Frequent Contributor
  • **
  • Posts: 266
  • Country: gb
Re: ft-901dm ham radio repair.
« Reply #131 on: December 17, 2015, 10:58:02 pm »
Thats true! we do have cats and dogs in some shops, the smaller shops that is, obviously not the larger stores.. My partner is German, and she had a shop with a cat on the counter for many years.. So not just the UK it seems.
Got wayyyy too many cat pictures!!! but i'll see if i can fine something small enough to post. Dont want to go crazy.
How about you, you have two catties?
 

Offline drforbin

  • Regular Contributor
  • *
  • Posts: 97
Re: ft-901dm ham radio repair.
« Reply #132 on: December 18, 2015, 02:18:43 am »
ok....thanxs so much for your cat pictures. I have four of them, older kitties.
They are also my best friends.


I think your correct. The lcr meter just can't measure the the inductance because it's not at RF.
Ok I put it back together and peaked everything including l09 and I'm getting REALLy good power on everything except 40m when the alc is connected AGAIN.


I just can't figure this out.

Perhaps I could ask this. What is the theory of operation of the ALC?
it's my understanding it should only register peaks where the excursion of the waveform is positive.
 

Offline AF6LJ

  • Supporter
  • ****
  • Posts: 2900
  • Country: us
Re: ft-901dm ham radio repair.
« Reply #133 on: December 18, 2015, 04:02:53 am »
ok....thanxs so much for your cat pictures. I have four of them, older kitties.
They are also my best friends.


I think your correct. The lcr meter just can't measure the the inductance because it's not at RF.
Ok I put it back together and peaked everything including l09 and I'm getting REALLy good power on everything except 40m when the alc is connected AGAIN.


I just can't figure this out.

Perhaps I could ask this. What is the theory of operation of the ALC?
it's my understanding it should only register peaks where the excursion of the waveform is positive.


I told you what to do about the 8.9MHZ trap L09
 |O

ALC stands for Automatic Level Control.
Its function is to keep the PA from being overdriven which would cause flattopping of the signal and result in excessive distortion products known as splatter.
Sue AF6LJ
Test Equipment Addict, And Proud Of It.
 

Offline drforbin

  • Regular Contributor
  • *
  • Posts: 97
Re: ft-901dm ham radio repair.
« Reply #134 on: December 18, 2015, 06:02:37 am »
AF6LJ, along with everyone else. I just wanted to thank you all.
Firstly I do know what ALC means I was just asking the theory of operation for a class 'B' which is what I believe this unit uses.

ok, here is update.
I resoldered the choke and realigned everything again,
This time messing with L09 in the process.
It's alittle to soon to tell but it looks like I'm staring to get more power on 40m.
I did nothing different than this time fiddling with l09.
So it seems AF6LJ may be correct.


AF6LJ, I would like to ask this if you donot mind.

I understand your statement about using direct connect at the 50 ohm, but if you look at my video where I was sniffing the phono jack there was no direct connection and I did not see a 8.9Mhz pass through. Now it appears you may very well be correct that the ALC is seeing another signal and responding to it, but we did not see a 8.9Mhz signal on SA. Any idea why?

And in order for the ALC to be attenuating the desired signal too much would the amplitude of this unwanted signal had have to have been larger than the desired  signal.


Thank you for bearing with my ignorance. My background is in digital electronics and programming. This is my first attempt at RF and I obviously have alot to learn.

thank you all.
 

Offline voltz

  • Frequent Contributor
  • **
  • Posts: 266
  • Country: gb
Re: ft-901dm ham radio repair.
« Reply #135 on: December 18, 2015, 09:57:43 am »
We seem to be going in circles here.. L09 is short circuit at 40m [EDIT: this comment was wrong, see later]. Its that simple really. It cannot be an IF trap at 40m.
Besides, its not a tuned circuit. Its just a coil without a cap. A trap it is not. There's no doubt about it.

As said, its just a preselector range extender for 160 and 80. Most likely to improve RX TX prselector tracking on those bands.

There is next to no 8.9Mhz on the SA because there is none. 50 ohms has nothing to do with it, that would only load the mixer slightly but not effect its resultant frequencies - its a low impedance mixer output (source/drain output and a forward biased switching diode)  so any effect is negligible.

And if when you do the short circuit coil test it DOES have an effect, then your band selector wafer s1-J is defective. Maybe check that it IS short circuit at 40, it should be according the the diagram, and locate the damaged wafer point.
« Last Edit: December 19, 2015, 02:03:25 pm by voltz »
 

Offline drforbin

  • Regular Contributor
  • *
  • Posts: 97
Re: ft-901dm ham radio repair.
« Reply #136 on: December 18, 2015, 10:38:04 am »
I agree. I donot see any 8.9Mhz signal. In fact I checked again tonight.
BUT, you should check the schematics again. The choke is only shorted 20m and higher freqs.
160,80,40 it is in effect. It's crazy, I donot know what it's doing BUT.
I realigned fully and I'm getting pretty much full power now on 40m.

I will make a video detailing everything.

In fact when I turn the choke I can reproduce the 10 watt problem I was having on 40m,
so something is going on. The real question now is what.
As I said I checked the SA again (sniffing this time) and I'm a 7Mhz signal and two harmonics.
Each harmonic lower than to prior. This is not want is effecting the ALC.
Could it be that the choke is somehow damping the feedback. notice the plate of the finals is feedback.

I'm at a loss.
I really would like to understand this.


Thank you.
 

Offline voltz

  • Frequent Contributor
  • **
  • Posts: 266
  • Country: gb
Re: ft-901dm ham radio repair.
« Reply #137 on: December 18, 2015, 10:46:38 am »
Look at S1-J again. I agree its not exactly clear how it operates but the default position shown is at 160m. So with that, follow the positions and shorting of L09 starts at 40m. Well, according to my eyes.
 

Offline voltz

  • Frequent Contributor
  • **
  • Posts: 266
  • Country: gb
Re: ft-901dm ham radio repair.
« Reply #138 on: December 18, 2015, 11:03:26 am »
As a clock face, i see contact 11 o'clock as closed on 160m .. then its two clicks clockwise and then its 1 o'clock short. Thats 40m.

They have drawing the inner common contact in a slightly ambiguous way. I guess the best way to resolve this is to manually examine the wafer with a spy glass.
 

Offline drforbin

  • Regular Contributor
  • *
  • Posts: 97
Re: ft-901dm ham radio repair.
« Reply #139 on: December 18, 2015, 11:04:14 am »
it rotates counter clockwise and the bias for the driver plate flows through it, and through l09.
look at the full schematics it has arrows showing rotation.
I have also confirmed this with dmm
 

Offline voltz

  • Frequent Contributor
  • **
  • Posts: 266
  • Country: gb
Re: ft-901dm ham radio repair.
« Reply #140 on: December 18, 2015, 11:10:25 am »
Hmm, well there's no arrows on the final PA diagram and its clearly shows the band positions in the key at the bottom! Which is clockwise.
Your DMM may show as 40 open, but according to this diagram, that's a fault. Can you visually inspect the wafer. Whats actually true?
 

Offline drforbin

  • Regular Contributor
  • *
  • Posts: 97
Re: ft-901dm ham radio repair.
« Reply #141 on: December 18, 2015, 11:14:57 am »
no..look at this (attached).

It rotates counter clockwise.

three clicks counter clockwise would find it on 20m and shorted at that point.
This in fact make sense. 20m and above were working.

160,80,40m were having varying degrees on ALC anomaly.
The question is how.
 
 

Offline voltz

  • Frequent Contributor
  • **
  • Posts: 266
  • Country: gb
Re: ft-901dm ham radio repair.
« Reply #142 on: December 18, 2015, 11:31:22 am »
Dammit our diagrams are different!!! Thats not what I have here. No arrows and a band select wafer key.

Ok, so yours at least has a arrow for direction, thats clearer than what i have.

So yes, you are correct it starts at 20 and L09 is operational at 160, 80 and 40. However, its still not a trap. It simply means the preselect coil is extended at 160, 80 and 40. All other bands its shorted out.  I was 1 click out.

When you adjust L09, you will see an effect on 40, its peaking the preselect alignment on TX. So just peak it. Then re-check RX is peaking is at the same point.
 

Offline drforbin

  • Regular Contributor
  • *
  • Posts: 97
Re: ft-901dm ham radio repair.
« Reply #143 on: December 18, 2015, 11:37:59 am »
I don't think it is a trap. But somehow when peaked it's fixing my problem.
I'll do a video later.

I'll also sniff it on the SA for everyone.
 

Offline voltz

  • Frequent Contributor
  • **
  • Posts: 266
  • Country: gb
Re: ft-901dm ham radio repair.
« Reply #144 on: December 18, 2015, 11:41:34 am »
Exactly. Just peak it - but please do re-check the preselect tracking between TX and RX is correct. Both should obviously peak at the same time. L09 will effect tracking on 160, 80 and 40m.

So if i read you correctly, did this resolve the issue and you have full power on 40 with ALC correct?
 

Offline drforbin

  • Regular Contributor
  • *
  • Posts: 97
Re: ft-901dm ham radio repair.
« Reply #145 on: December 18, 2015, 11:47:01 am »
It seems so...I'll double check everything later and do a video.
I reconnected the ALC it seems to be working.
I just don't know why it's working.
 

Offline voltz

  • Frequent Contributor
  • **
  • Posts: 266
  • Country: gb
Re: ft-901dm ham radio repair.
« Reply #146 on: December 18, 2015, 12:01:29 pm »
Excellent!

Its working because L09 was indeed out of alignment. But not because of not rejecting any IF signal, its wasn't tuned to an IF - there was no IF present, but because the energy was being rejected back to the C01 Rf input pin. Rather like a bad SWR with reflected energy. This caused the amplitude to be magnified (like a resonance) and that boosted the ALC rectifier voltage way too much cutting back the power.

So that simple alignment had a knock back all the way back to the ALC.

Its always easy to say after an event i know, but it does make complete sense.

Some things have been learned:

Yeasu diagrams are misleading! Compare different versions.
LCR meters are not very good when it comes to measuring RF coils (dust iron cores for sure) Make a tuned circuit.
Stay calm and logical. We all did. Well done everyone.
RF sniffer loops are your friend in the RF world.

 

Offline drforbin

  • Regular Contributor
  • *
  • Posts: 97
Re: ft-901dm ham radio repair.
« Reply #147 on: December 18, 2015, 12:07:38 pm »
Well...I thank all you guys. You all were great. I will do a wrap up tonight..
I'm pretty sure it's correct.
So you think the signal being delivered to the finals was to high, and the alc was picking up on that?
Yes, the manuals is quite bad.
In fact the  alignment procedure has to be interpreted in places.

must be translation problems.
 

Offline voltz

  • Frequent Contributor
  • **
  • Posts: 266
  • Country: gb
Re: ft-901dm ham radio repair.
« Reply #148 on: December 18, 2015, 12:13:28 pm »
"So you think the signal being delivered to the finals was to high, and the alc was picking up on that?"

Yes. because of the reflected energy from the miss-aligned coil.

Look forward to your wrap up video :) Its quite possible this thread could become a reference to others with the same problem. No its not the mode switch!!! :)
 

Offline drforbin

  • Regular Contributor
  • *
  • Posts: 97
Re: ft-901dm ham radio repair.
« Reply #149 on: December 18, 2015, 12:23:53 pm »
Yeah....This is quite a strange problem.
I hope we can keep in touch.
You too AJ.

As I said, when I tune the l09 I can reproduce the effects I was seeing.
If your correct I suppose it should mean the finals are not being driven as hard.
I was getting about 185-200volt p-p on on the other side on c01 coupling cap.
I'll test and see what I'm getting now.

Man this RF stuff is crazy! O0
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf