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 pienari » 09 Jan 2018, 13:10

This is getting intresting what it chould be.

Have you measured xtal X1 rx / tx ?.
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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 » 09 Jan 2018, 16:00

Interesting indeed! :D

I have not measured freq around X1 (10.240MHz) to check if that is different during RX and TX.
Mainly due to the fact that TP1 where I measure now and see the 800Hz up-jump in TX mode is the mixer input on pin 4 on mixer IC 2 and it is coming more or less directly from the crystal bank area (OSC 2).

I am using an 10Mohm osciloscope probe with a 1000pf ceramic cap on the tip when measuring in order to avoid too much loading on the circuit being measured. What place would be the best to measure it properly during RX and TX without loading it so that the oscillating freq gets affected?

Would pin 3 on PLL02 work or emitter of Q1?
PTBM131A4X - X1 oscillator area.jpg
I will measure tonight when I am back at home.
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Last edited by CrazyFin on 10 Jan 2018, 08:34, 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 CrazyFin » 09 Jan 2018, 20:32

Back at home now in my geek-labb... :geek: :lol:

Ok I measured at two points:
Q1 emitter and see 10.240020MHz in RX and approx 40Hz higher in TX = 10.240061MHz (using my freq counter via 1000pf ceramic cap and freq counter has a GPS 10MHz freq standard as its reference).

I then realized that measuring at pin 3 on PLL02 (IC1) is also good since that is indeed the reference oscillator input for the PLL.
So pin 3 @ IC1 is showing 10.240024MHz in RX and 10.2400066MHz in TX. So TX is about 42Hz higher which is fine.
I just wish that this board would have a trim cap for adjust this reference oscillator since the TX freq of 10.240066MHz is sliiiiiightly higher than specs.
Service manual says to check for 10.240000MHZ +/- 50Hz.

I guess I could change the value of C4 to a SMALLER value to lower the frequency?
Or shall I just replace it with a trimcap. I have a couple of trimcaps that ranges from 5.5 to 65 pf that should work and give me enough adjust range or is a trimcap with tighter range better?

So anyway, this confirms that the freq jump of 800-900Hz in TX (or the other way around RX freq is 800-900Hz too low) is indeed somewhere in the fine- and coarse tune circuits.. :shifty:

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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 » 09 Jan 2018, 21:49

I read through the entire thread again and checked through my notes.

Biggest difference in your (@pienari) and my measurements is the measurement on the left side of R21, the 100k resistor that goes to cathode of varactor diode D6.

You measured 2.94V in RX and 2.85V in TX, that is a drop of 90mV going from RX to TX

When I measure on the left side of R21 I get 3.862V in RX and 3.84V in TX and that is a drop of 22mV, i.e. I get a much LOWER voltage drop on the cathode D6 when going from RX to TX!

Note also that my voltage is about 922mV higher than yours in RX and my TX voltage is about 990mV higher than your drop.
This could of course be caused by the fact that your fine tune clarifier (for RX only) and coarse clarifier (for RX and TX) is designed slightly different.

So I tested with DECREASING the voltage drop resistor R16 that comes into play in TX. I changed it from 6.8K to 3K and now TXfreq - RXfreq = 350Hz instead of 850Hz. HOWEVER, with this decrease of R16 from 6.8k to 3k my RX fine tune range drops from +/-800Hz to +/-350Hz... {bnghd}

Replacing R16 from 6.8k down to 120 ohms and RX freq = TX freq (diff is less than 10Hz!) but NO fine tune range at all... :crazy:

So how can I drop R16 closer to zero BUT keep the RX clarifier range intact at 1.6kHz (+/-800Hz)?

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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 » 10 Jan 2018, 09:27

I donno my meters accuracy 100% but my freq meter show pll pin3 10.239922 rx and 10.239962 tx. (27.205065MHz ant line.) AM

Yes measured from R21 rx pot turned left 0.944v and right 6.01v , TP1 20.102398MHz and 20.107486MHz.
Clarifier knob pulled R21 0.973v and 6.16v , TP1 20.102452MHz and 20.107573MHz.
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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 » 10 Jan 2018, 19:51

Ok then you and I are pretty close on the X1 freq shown on PLL02 pin 3. You have also approx 40Hz diff between RX and TX.

Alright, I am taking somewhat new approach trying to figure out what is going on:

1. In RX mode I have 3.834V on left side of R21 (100k) and 0.922V on left side of R11 (100k) meaning that varicap diode has 2.912V bias in RX mode

2. In TX mode I have 3.821V on left side of R21 and ONLY 0.00246V on left side of R11. This means that the bias over varicap diode has now dropped 0.868V during TX compared to RX. So instead of having 2.912V over D6 in RX mode I see 3.78V in TX over D6.

3. A higher voltage on cathode D6 = less capacitance = higher freq? Am I right?

4. If no 3 is true then I need to figure out why I only get 0.00246V on the left side of R11 in TX mode. This voltage should be approx 0.868V higher to keep the voltage level at anode D6 same as in RX (since D6 cathode voltage level only changes a tiny -13mV from RX to TX)

And you know what! If we look back in this huge thread (me writing fault tracing novels :D ), we can recall that we loosely discussed the somewhat LOW voltage level of AVR regulator Q36 showing "only" 9.027V in RX and 8.928V when the transistor voltage chart (page 22 at Cybernet Export Service Manual) shows that Q36 emitter voltage in RX should be around 10.83V! I am 1.8V too low!

Q36 base voltage shows around 10.1V in both RX and TX and Q36 collector voltage shows proper 13.65V in RX and drops tiny to 13.45V in TX.
Remember also that I replaced Q36 from original 2SD837 to a BD645 but that made no difference.

So the question is: What the heck is pulling the voltage, in BOTH RX mode and TX mode so that it ends up 1.8V lower than it should be?! :crazy:

I initially tested with lifting R17 (which already had measured ok) but that made no difference.
Remember also that I have el-caps C180 and C179 with brand new ones (even though the old one measured ok in both capacitance AND ESR).

Suggestions on the next steps?
Remove R168 or R176 (ground side of VFO, the coarse clarifier that is active in both RX and TX) or something else?
I need to figure out why Q36 emitter voltage is around 8.9/9V instead of 10.8V in BOTH RX and TX.... :roll:

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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 » 10 Jan 2018, 20:55

Hmmm I probably getting too excited here... :cry:

Assuming a typical base -> emitter voltage of BD945 of approx 0.5V (according to datasheet) and with the D55 zenerdiode HZ11A3 that has about 10.1V zener voltage according to its datasheet (HZ11A3), I should see 10.1 - 0.5 = 9.6V emitter voltage on Q36.
Assuming 0.7 base -> emitter voltage I should see around 9.4V which is not so much higher than the 9.03V I see.

Yes, it is about 300mV too low according to this but it is not enough to compensate for the 868mV that is "missing" on anode D6 in TX.

Question is why the transistor voltage chart I refer to in my previous post is indicating that we should see 10.83V. Shouldn't emitter voltage be about 0.5 to 0.7 lower than the base voltage which is indicated to be 10.05V in the transistor voltage table?

And what can I do to get left side of R11 to increase about 868mV so that the voltage over D6 stays the same in both RX and TX?

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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 » 10 Jan 2018, 22:02

I writed that zener number wrong . sorry.. yes of course it is D55 .
If you like test a bit higher voltake just add 1n4005 diode series to D55.
Not remember witch way maybe anode to ground.

It should give extra 0.5v.

Every Cybernet that regulator voltage is about 9v .
I donno where that 10v in measured,chould it be just mistake?.
Nah.. i have to go sleep now.
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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 » 10 Jan 2018, 23:22

Ok so if we assume that the 9V I get at Q36 emitter is fine then there MUST be something else causing the left sides of both R11 and R21 to have too big difference between RX and TX.

As I mentioned above I see a difference of approx 868mV.

So here is what I did now before bedtime:

1. I lifted anode D8.
2. Measured R13/R14 conjunction where anode D8 normally is connected and I see about 5mV in RX and 1.589V in TX.
3. I feed anode D8 with 1.6V AFTER that I started to TX. WHAT THE HECK! TX freq now MUCH lower than RX freq. The other way around!!
4. I feed anode D8 with 1.35V. Wohoooo! Only 10Hz difference!!
5. I kept lower voltage to anode D8 and when I remove the voltage from anode D8 the TX freq jumps back up to 850Hz higher than RX.

Looking back at my post #30 in this thread I see that I measured anode D8 (when D8 was in place) to about 7mV in RX and 1.29V in TX.
Ahaaa, the TX freq is very sensitive to the voltage being fed to anode D8 while in TX!

Maybe I should try with a trimpot at R14 instead of a fixed resistor value? Then I can adjust TX freq to be as close as possible to RX freq but would a change in the value of R13 (or R14) affect the range of the fine tune (RX only) as it has done when I have changed other resistor values in the two different clarifier paths?
Last edited by CrazyFin on 11 Jan 2018, 19:55, 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 CrazyFin » 10 Jan 2018, 23:54

WOHOOOOO! :shock:

I think I have solved it!! :ugeek:

I replaced R13 (fixed 15K) with a trimpot 100K.
After some initial tuning I have now RX freq = TX freq within 10Hz!! 8)

Fine tune clarifier works also with a range of +/- 800Hz as wanted and coarse tune works as well (+/- 5 to 7 kHz)

I am too tired now and time for sleep but tomorrow I´ll desolder the trimpot again and check what value it has.
It was VERY sensitive though which is probably caused by me using 100K when I might have been better of with 50K or even lower.
Anyway I´ll desolder the trimpot and measure its value tomorrow... Time to :yawn:

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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 » 11 Jan 2018, 00:13

Maybe I should try with a trimpot at R14 instead of a fixed resistor value? Then I can adjust TX freq to be as close as possible to RX freq but would a change in the value of R13 (or R14) affect the range of the fine tune (RX only) as it has done when I have changed other resistor values in the two different clarifier paths?
It shouldnt as that voltage drops to 5mv in RX which isnt enough to bias D8 on you also get a voltage drop of about 0.7 across a diode
So basically the voltage from D8 was too high???

I would try changing R13 for a variable of say 20k?

Stop Press Stop Press EDIT.
You just posted as I was writing this!

WELL DONE!
I would maybe fit a multi-turn preset making it easy to set your wanted voltage a lot more accurately.
Again WELL DONE! :clap: :clap: You stuck to it and worked it out!

FFF
Well pleased for you. :D :D
ʎɐqǝ uo pɹɐoqʎǝʞ ɐ ʎnq ı ǝɯıʇ ʇsɐן ǝɥʇ sı sıɥʇ

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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 » 11 Jan 2018, 22:08

Puih thanks for helping me and discussing the issue with me. Your inputs made to think more than twice and really try to understand what is happening in the RX and RX/TX clarifier paths.

Yepp, delta-voltage at the left side of R21 and left side of R11 dropped about 868mV when going from RX to TX.
Delta-voltage of left side R21 RX->TX was only 12 to13mV
Delta-voltage on left side of R11 RX->TX was 920mV so figured out that there MUST be a to big drop on the left side of R11 and that is connected to cathode D8 and then I started to think that if there was a too big drop in voltage on voltage divider R13/R14 where the anode of D8 is connected and voilaaaaa! After lifting anode D8 and then feeding various voltages there I could see what voltage would keep the voltage over varicap D6 constant during RX->TX.

I´ve ordered some multi-turn (5-25 turns) trimpots in various values (from 20k up 100k) from my local electronics supplier and they should arrive some day next week.

I desoldered the current trimpot and measured the value it was set to and it shows 56k?! Quite high compared to the original value for R13 of 15k... :shock:

I will test tomorrow evening with a 56k fixed resistor to see if this value really is correct.
I guess the need of a much higher R13 value is caused by the fact that I have some hundred millivolts too low emitter voltage on Q33 compared to for example what@Pienari has. With too much drop over R13 the D8 never opens up and thats why left side of R11 dropped from 922mV to 2.4mV to anode D6 when going RX->TX.
I did remove all transistors in that RX/TX switching circuit and they all were fine and I even tried with new fresh transistors but still the same values.

Anyway, I´ll tidy up all the test wires and components during the weekend and then finalize the radio with a final alignment and tune-up and the out on the market for sale. :thumbup:

Then a few days of the bench to get ready for 3 of the CRT Hercule Turbo / Galaxy Saturn Turbos that needs to be "de-modified" and fixed. :roll:

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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 » 11 Jan 2018, 22:35

Good work and it take only a bit sisu. ;)

I think i test 20k trim pot to R13 and i can get my radio fixed too.

Then 5pcs M588:s . Concorde 3, Kraco 2555fm , Ham multimode 2, another Colt Excalibur ssb without fm what i have to install... oh. where we can get time to repair all radios.
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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 » 12 Jan 2018, 15:08

@pienare

He he yepp, I'm gonna relax with a loooong sauna and "lonkero" tonight when I come home. :D
(By the way, where in Finland are you located? We used to have a summer house near Tampere / Kyröskoski, right between the extremely small villages Viljakkala and Luhalahti but I have relatives all over in Finland.)


Waoh! Seems like you have as many radios as I have staring from the shelves screaming for repair/fix/mod... :lol:
I have 3 Kraco 2555FM:s that are waiting in line and one of them has been rebuilt to 200 channels AM/FM/SSB with a 40 pos channel selector. :geek:
I just need to expand the RF stages a little bit more so that it will have enough power on the outer bands as well.

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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 » 12 Jan 2018, 16:18

Well i cant find R13 ,or its marked bad but i think its near to R14 and resistor is not on board . :crazy:

I live in Jääli .Jääli is 15km east from Oulu .
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