Petrusse Excalibur 2002 (PTBM131A4X) - TX freq off approx 1.7kHz in all modes and all bands, RX seems ok

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Re: Petrusse Excalibur 2002 (PTBM131A4X) - TX freq off approx 1.7kHz in all modes and all bands, RX seems ok

Post by CrazyFin » 05 Jan 2018, 11:27

I found this interesting website about how clarifier (RX only) works in most Cybernet radios and how to unlock them for TX use as well:
http://www.cbtricks.com/handyandy/PC-122/Clarifier.htm
Very good explanation of how this part of the circuitry works and also good explanation of the varactor diode's function in this circuit.

Note that there is a trimpot (VR3) in the example to keep TX freq centered when going from RX to TX.
Note also that the RX line in this example goes to cathode of the varactor diode while the TX line goes to the anode side, i.e. totally opposite compared to our boards.

I am starting to think that I should think reverse in my fault tracing and I am wondering if the fault is in the RX line of my clarifier and the freq in RX mode? Maybe TX line is properly adjusted and works as it should but when going back to RX mode the voltages are wrong causing the RX freq to be off and since I am using RX mode to adjust the local oscillator it ends up being wrong BUT it looks like it is the TX mode that is wrong.

I´ll keep on poking around in this area and as soon as I get some voltage measurements from @pienari I can make the decision if I should test to replace the Q36 AVR transistor and/or any of the DC switching transistors Q33, Q34 and Q35.

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Re: Petrusse Excalibur 2002 (PTBM131A4X) - TX freq off approx 1.7kHz in all modes and all bands, RX seems ok

Post by DX-Digger » 05 Jan 2018, 16:29

First thing that mod is for radios that dont have variable TX frequency just Clarifier but his explanation is very good.

Your radio has variable TX and a clarifier, there is no adjustment via the TX, no trim pot as I can see.. I also cant find one for the clarifier. So you may of hit the nail on the head and the rx LO needs to be adjusted to match the tx and rx frequency.
If that is the case then you deserve a pat on the back because I would never of thought of that!
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Re: Petrusse Excalibur 2002 (PTBM131A4X) - TX freq off approx 1.7kHz in all modes and all bands, RX seems ok

Post by CrazyFin » 05 Jan 2018, 16:40

Yepp I realised that the mod/explanation I linked to was for radios with a RX clarifier only but I thought his explanation of how it works was excellent.

And yes, there is NO trimpots available for center frequency of clarifier/fine tune (RX only) and the coarse tune (TX and RX and called VFO on my radio).
So maybe it is better that I experiment with changing one of the resistors in the RX only clarifier path in order to set the RX clarifier center in line with the center of the coarse clarifier.

:think: Being a 100% "fin" but born in Sweden I guess I need a sauna first in order to be able to think clearly! :ugeek: :lol:

Back later tonight with "labb-report"... :P

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Re: Petrusse Excalibur 2002 (PTBM131A4X) - TX freq off approx 1.7kHz in all modes and all bands, RX seems ok

Post by pienari » 05 Jan 2018, 16:57

Q36 emiter AM rx = 9.51v
Q34 AM rx e = 8.72v c = 9.5v b = 9.38v tx e = -0.21v c = 9.44v b = 0.1v
R21 (100k ohm) 2.94v rx 2.85v tx.
R11 not on board.
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Re: Petrusse Excalibur 2002 (PTBM131A4X) - TX freq off approx 1.7kHz in all modes and all bands, RX seems ok

Post by 14CS06 » 05 Jan 2018, 20:51

Hello

A few schematic PTBM131A4X

Image

Image

Image

Image

Image

Image

@+
Claude
Last edited by 14CS06 on 13 Apr 2018, 17:16, edited 1 time in total.
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Re: Petrusse Excalibur 2002 (PTBM125A4X) - TX freq off approx 1.7kHz in all modes and all bands, RX seems ok

Post by CrazyFin » 05 Jan 2018, 23:26

@pienari: Thanks for the measurements!
I see that your Q36 emitter voltage is 9.51V (service manual says 10.83V) and mine is 8.98V which is about 0.53V lower than yours.

May I ask you for some few more measurements please:
Voltage of emitter Q36 when in TX (AM mode)? (Too see how much it drops when going from RX to TX.)
Voltage of collector Q36 in both RX and TX (AM mode)? (Too see voltage level of your DC supply.)

Strange that you do not have R11 on your board? Are you sure that you really have the PTBM131A4X? All of those boards I have seen do have the R11 on the board. Value is 100K ohm for both R11 and R21 as far as I can read out from the schematics.
If you do not have R11, can you please try to measure the anode of varactor diode D6 or the junction of D7 and D8/R16? Both RX and TX please (AM mode).

Does your base station say COLT Excalibur SSB on the front or does it say Excalibur SSB (without COLT)?


@14CS06: Thanks for the schematics! Unfortunately they have too low resolution to be helpful when one zoom in on them but I have different variants of the PTBM134A4X as well as the PTBM125A4X (which is the board for my Petrusse Excalibur 2002). I even have them in paper format (got them with the book Export Service Manual from CBC International).

I´ve uploaded quite decent and high resolution schematics for PTBM134A4X and PTBM125A4X to my Google Drive:
https://drive.google.com/open?id=0B7z6W ... i0ySkFEdXc

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Re: Petrusse Excalibur 2002 (PTBM131A4X) - TX freq off approx 1.7kHz in all modes and all bands, RX seems ok

Post by pienari » 05 Jan 2018, 23:46

Yes i can measure it tomorrow but i remember psu voltage is 14.6v.

Ok it goes that way , when voltage drops output of Q36 freq goes hi.
When i measured T1 rx tx freqs there was a bit difference and in tx freq goes up so voltage in Q36 have to drop too much in your case. :think: So there is the issue.

In my case someone have chanced Q36 lower current transistor i have to chance it too.

Maybe i get better result after that .

Yes R11 place is empty.
I can take picture.
http://aijaa.com/pTZCMg
http://aijaa.com/kRvrHU
http://aijaa.com/3MT1U2
http://aijaa.com/c0ETrl
Last edited by pienari on 06 Jan 2018, 00:21, edited 2 times in total.
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Re: Petrusse Excalibur 2002 (PTBM131A4X) - TX freq off approx 1.7kHz in all modes and all bands, RX seems ok

Post by CrazyFin » 06 Jan 2018, 00:17

@pienari: Wonderful! Thanks for the pictures!
It is VERY interesting since both you and me have the SAME board (I checked mine as well now and it actually says PTBM131A4X also!)

I see now that you indeed have no R11 as well as no R16 and no C20 but I think that your COLT Excalibur SSB is that by default.

I just replaced my Q36 from 2SD837 to TIP20 and I also tried with BD645 and no change. Still the same emitter voltage (about 8.8 to 8.9V) with both TIP20 and BD645.

In your case I guess you could get better SSB result if you replace the "weak" 2SD325 with either 2SD837 or the stronger TIP20 and BD645.

Ok cool, I´m looking forward for getting your measurement result for
Voltage of emitter Q36 when in TX (AM mode)? (Too see how much it drops when going from RX to TX.)
Voltage of collector Q36 in both RX and TX (AM mode)? (Too see voltage level of your DC supply.)
Voltage at anode of varactor diode D6 or the junction of D7 and D8/R16? Both RX and TX please (AM mode).

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Re: Petrusse Excalibur 2002 (PTBM131A4X) - TX freq off approx 1.7kHz in all modes and all bands, RX seems ok

Post by pienari » 06 Jan 2018, 00:28

Yes i will measure tomorrow.
Can you measure current from Q36 emiter rx tx ?.
Check zener D66 what regulate output voltage of Q36.

I have to get some sleep atm. . .
Last edited by pienari on 06 Jan 2018, 10:35, edited 1 time in total.
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Re: Petrusse Excalibur 2002 (PTBM131A4X) - TX freq off approx 1.7kHz in all modes and all bands, RX seems ok

Post by pienari » 06 Jan 2018, 10:29

Ok. Q36 rx e = 9.51v tx e = 9.47v Q36 rx c = 14.58v tx c = 14.2v

D6 anode is connect to ground.
D7 rx = 3.64v tx = 3.33v
D8 rx = 0.04v tx = 3.44v anode wire goes to clarifier sw. selector pulled rx 0 tx 0.14v.
R16 not on board
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Re: Petrusse Excalibur 2002 (PTBM131A4X) - TX freq off approx 1.7kHz in all modes and all bands, RX seems ok

Post by CrazyFin » 06 Jan 2018, 21:25

@pienari: Thanks for your measurements.

After replacement of Q36 from 2SD845 to BD6435 have now around 9V on Q36 emitter in RX AM and it drops about 30mV to 8.97V in TX AM, i.e. almost same drop as you have (you have 40mV drop) so I think my regulator/DC switch section is good even though my levels are about 0.5V lower than yours.

I am more into the path now that it is the fine tune clarifier path, i.e. the one that is ONLY active in RX that has some bad components since the coarse clarifier that is active in BOTH TX and RX is about 800Hz higher when I go into TX mode.

So in RX I have no voltage applied to cathode of D6 and voltage level on anode D6 is affected by fine tune pot. When Fine Tune is in middle I have approx 0.847V and to outer right I have 0.9mV and outer left I have 1.505V. So a span of about 1.5V. Middle should then be 0.75V instead of the 0.847V I see.

In TX the anode D6 voltage level drops to 1.62mV and cathode D6 shows 3.805V in TX (RX 3.825V) but as I mentioned before, measuring at D6 cathode affects oscillator frequencey due to loading the circuit.

My steps now are to check R11, C20, D7 and R12 that all are in the RX path of the fine tune that is only active during RX.
I also need to check R13, R14, R16 and D8 since they clearly AFFECTS the FINE tune path in TX as well even though this path normally is active in RX only and then also will affect the voltage level at anode D6.

I think it is better for me to now focus on getting anode D6 voltage level proper in RX so that when I go TX and anode D6 drops (currently to 1.62mV) it should drop the proper amount to compensate for the drop of 20mV on cathode D6.

Puih, I WILL NOT GIVE UP!! :lol: (@lbcomms: Pleeeeeease heeeeeelp! :wave: :? )

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Re: Petrusse Excalibur 2002 (PTBM131A4X) - TX freq off approx 1.7kHz in all modes and all bands, RX seems ok

Post by CrazyFin » 06 Jan 2018, 22:41

Alright I tested with replacing R12 (27K) with a trimpot of 50K and then re-tune CT3 to show 20.105 (+/-50Hz) in TX.
I now have perfect 27.205MHz in TX AM (ch 20).

When releasing in TX I have to move trimpot R12 to max (50K) in order to get closer but it is only getting up to 20.104533MHz so I am still about 533Hz too low on RX (or 533Hz too high on TX compared to RX). It is almost as if the whole clarifier (fine tune RX only) has too low resistance in order to keep the RX freq in line with TX freq (at least with the oscillators where the crystals X2,X3,X4,X5 and X7 are).

I measured Q34 emitter and I see 8.20V RX and -130mV in TX mode?! I am about 1V lower than expected voltage in RX mode.
Q34 collector shows 8.99V in RX and 8.94V in TX. I am about 1V lower than the expected voltage.
Q34 base shows 8.87V in RX and 33mV in TX so the base looks ok I guess.
(Voltages according to earlier posts in this thread: viewtopic.php?f=53&t=54813&p=497413#p497436

I am also trying to locate R15 8.2K that is connected to Q34 emitter but I just can't find it! :crazy:
I see Q34 emitter and there is a blue/white wire connected to it that goes to one of the outer legs of clarifier pot (via BR post).
Maybe it just doesn't exist since that would actually be a resistor of 8.2K in PARALLEL with the clarifier pot?

See schematics again with my red line showing paths active in BOTH TX and RX and green paths showing active only in RX. Note that the path going to D6 anode is active in both TX and RX BUT different paths generating the voltage:
PTBM131A4X - clarifier RX only and RXTX circuits- web version.jpg
Before going to bed I decided to desolder C20 ceramic cap at the anode of D6. Cap indicates good and shows 15nF at 200kHz with my Peak LCR45 but this is interesting! Frequency at TP1 is of course completely of and shows 20.112840 in RX but jumps ONLY 5 Hz to 20.112845 in TX!

I'll test tomorrow with a new C20 anyway if it is a component causing bad effect while in circuit but showing up as good on meter.

Nah, wait i minute! :ugeek: Just for fun I just bridged C20 so that D6 anode is connected to ground directly instead of that C20 cap (like you have @pienari) and hooooooooly shi-------t!! IT WORKS! After re-tuning CT3 to 20.105005 in RX I see 20.104994 in TX!! Only 11Hz difference betweeen RX and TX frequencies?! :shock:

Problem now is that fine tune has now effect at all in RX anymore which is of course clear since the RX path for the clarifier RX only to anode D6 is now always grounded.
So I replaced C20 with a fresh one and I am now back with 500Hz higher TX freq compared to RX (remember I still have the trimpot at R12 with its setting at max 50K).

It MUST be something in this RX path of the fine tune since I am able to get the local oscillator at TP1 to be now only 500Hz higher in TX compared to RX. Almost there at the solution now.... :roll:

Question is if I should INCREASE the R12 even more or what effect will C20 have if I replace it with a trimcap (and the effect of the fine tuning range)?
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Re: Petrusse Excalibur 2002 (PTBM131A4X) - TX freq off approx 1.7kHz in all modes and all bands, RX seems ok

Post by DX-Digger » 07 Jan 2018, 03:25

R15 is marked with a * on the diagram and it says (adjusted typical value shown)
Image

I am trying to get my head around what that tune circuit is doing.

C20 is in series with the capacitance of D6 so it lowers the overall capacitance of D6 and C20.

When RIT/Clarifier is on it adds voltage to the cold side thus lowering the voltage across D6 increasing the capacitance. raising or lowering the RIT voltage varies the D6 capacitance depending on where the RIT is set.

In TX mode Q35 has a voltage applied to its base which then grounds the voltage on the base of Q34 turning the clarifier voltage off or down to a very low level, and R13 R14 D8 and R16 should put a small bias inplace of the Clarifier voltage, infact if they put the same voltage as the clarifier has in its central position then the capacitance in D6 should stay the same unless the tune is rotated.

So what voltage are you getting from D8? in TX mode?
lift its cathode and measure it so you dont discharge c20/D6 you did say your voltage changed when you measured it.
if D8 is OC (open circuit) then check to see what voltage you get on its anode?

I am seriously suspecting D8 or maybe a resistor gone high value?
If its not that then I Give UP LOL
And its now 3:30am Im off to bed :D :D {bnghd} :D :D
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Re: Petrusse Excalibur 2002 (PTBM131A4X) - TX freq off approx 1.7kHz in all modes and all bands, RX seems ok

Post by pienari » 08 Jan 2018, 07:39

Clarifier is made a bit different in my radio.

http://aijaa.com/r9Flvc
http://aijaa.com/ooLluY
http://aijaa.com/L4uSHN
http://aijaa.com/Rg6uIG

And there you can see R15 8.2k resistor connected in clarifier pot.
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Re: Petrusse Excalibur 2002 (PTBM131A4X) - TX freq off approx 1.7kHz in all modes and all bands, RX seems ok

Post by CrazyFin » 08 Jan 2018, 20:48

@pienari:
Excellent, thanks for the photos!
Your clarifier and tune circuits are indeed somewhat different than mine even though we have the same mainboard PTBM131A4X.
As you have written before you don't for example have C20 and if I understood your correctly it is bridged with a jumper to the pcb ground or was it just left out so that the anode of your D6 is directly connected to cathode of D7 as well as cathode D8 (since your R11 was missing/bridged as well?).
I can see other resistors not being in place (like R16) as well and one of them you confirmed were sitting on the clarifier (R15).

I finally found the R15 sitting on the board right were TU connection point is. One of your picture helped me! :clap:


So to make a new write-up/summary of what we have investigated so far:

I have measured many of the components in the RX and TX paths for clarifier (called fine tune) and tune (called VFO on Petrusse Excalibur 2002).
Measurements done with the component out of circuit using either Peak LCR45 or Peak DCA55.
For the voltage measurements I have the negative cable of my bench multimeter HP34401A connected to PCB ground.
AM mode ch 20 (27.205MHz) Note that the problem is not depending on mode neither the band selected.

Link to schematics here: PTBM131A4X

R11 is ok, shows 98.4k
R12 is ok, shows 27k
R13 is ok, shows 15k
R14 is ok, shows 3.3k
R15 is ok, shows 8.02k
R16 is ok, shows 6.7k
R17 is ok, shows 7.9k
R18 is ok shows 5.5k
R21 is ok, shows 98.6k


C20 is ok, shows 15nF


D8 measures ok, shows 0.7 Vf with 4.7mA test current
With D8 removed TX freq at TP1 is still about 500-800Hz too high compared to RX freq at TP1.
D8 cathode shows 0.599V in RX and 0.7mV in TX
D8 anode shows 6.96mV in RX and 1.29V in TX


D7 measures ok, shows 0.7 Vf with 4.7mA test current
With D7 removed TX freq and RX freq differs only 10Hz! I will of course now have NO clarifier (fine tune) but tune works fine in both RX and TX (VFO on my Petrusse).
D7 anode shows 1.37V in RX and -79mV in TX (!! Negative voltage here in TX mode?!).
D7 cathode shows 0.598V in RX and 0.73mV in TX (both values almost identical with cathode D8 since the are connected)
With D7 removed:
D7 anode shows RX = 5.1V and TX -78mV
D7 cathode shows RX = 0.75mV and TX = 1mV (compared to 0.598V in RX and 0.73mV in TX when connected.)


D6 anode shows 0.591V in RX and 0.73mV in TX
D6 cathode is difficult to measure since it caused a loading effect on the TP1 measured frequency. It drops from 20.10505 to 20.100636 in RX and from 20.105905 to 20.100890 in TX but as you can see while this loading effect is in place (due to me probing with multimeter probe at D6 cathode) the difference in RX and TX freq on TP1 decreases from about 800Hz to only 254Hz difference (still a little bit too much difference though)


Q36 (2SD837 that I have replaced with BD645 but no difference)
Q36 base RX = 10.168 and TX = 10.157V
Q36 collector RX = 13.70 and TX = 13.46 (power supply is a linear 13.8VDC PSU with 30A capacity, internal PSU not used during these tests)
Q36 emitter RX = 9.1V and TX = 9.05V (drops initially to about 8.9V but after 1 minute TX it is up at 9.05V)


Q34 emitter RX = 8.216V and TX -0.137V (negative again!)
Q34 collector RX = 8.988V and TX = 8.952
Q34 base RX = 8.87V and TX = 32mV


Q33 collector RX = 35mV and TX = 8.86V
Q33 emitter RX = 8.988V and TX = 8.952 (same as Q34 collector)
Q33 base RX = 9.02V and TX = 8.23

What I have not done:
Replaced varactor diode D6
Replaced diodes D7 and D8.
Maybe I should try this even though D7 and D8 measure ok out of circuit.
I don't know how to verify the D6 varactor diode though so I guess I should just try with replacing it. ITT310 is not made any more and difficult to source. Any good equivalents? BB102, BB103, BB131, BB139 or even 1S2687? I do have a few 1S2687 here in my storage.
Is NTE614 a good equivalent as well?

UPDATE: Replaced D7 and D8 with 1N4148 instead of 1N4448 but no change. RX freq still about 800-900Hz lower than TX.

UPDATE 2: I have to move the FINE TUNE (clarifier) to almost full right position to get RX freq and TX freq to be the same. At this point the pot measures almost 10K which is the max value for this pot VR3. Even if I add series resistance with the slider leg from anything of 10K up to 50K I just get a small bit closer to each other and the effect is just that I am reducing the range of the clarifier instead of actually getting RX freq closer to TX freq.

I am now kind of stuck here and I am not sure what to do now... :?
Hopefully some pair of new eyes (and brains) that reads my summary above and checks the schematics will have a simple explanation to my issue

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