CRT Hercule Turbo - EPT295013Z - Can not tune PLL voltages

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CrazyFin
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CRT Hercule Turbo - EPT295013Z - Can not tune PLL voltages

Post by CrazyFin » 08 Dec 2017, 10:39

Alright, I have 3 (!!?? :D :shock: ) CRT Hercule Turbo. Yepp 3 in total and all of them need care and repair for different problems... :crazy:

The CRT Hercule Turbo is also known as the Galaxy Saturn Turbo / Alan 560 / RCI-2990. These base rigs have the extra amp mounted on the back of the unit. (A couple of threads already on these units in this forum.)

Motherboard is the EPT295013Z and good schematics can be found at CBTricks:
http://www.cbtricks.com/radios/rci/rci_2970/
You can also use the really nice modern created schematics for the RCI-2950 (same motherboard)made by Rick Jackson CB: http://www.cbtricks.com/radios/rci/rci_ ... 50_sch.pdf
Crystal clear schematic! :ugeek: (Thanks Rick for all these good schematics you've created!)

Anyway, back to my first of my three CRT Hercule Turbo and the first problem:

1. Radio overall in good condition and I can't see that there has been any hack mods done. All looks actually quite original with some transistors been swapped out (with same type as original).

I found a "blown" electrolytic cap C204 near the IC6 (7808A) that I replaced.
Completely broken! (component layout at http://www.cbtricks.com/radios/rci/rci_ ... layout.gif).
CRT Hercule Turbo - C204 blown - 3.jpg

2. Radio has problems with intermittent no RX and no TX. Actually more often RX is sooooo silent and when PTT the TX light goes on but no output power. This is with radio in all modes and around 27.200-27.600MHz.

Ok, so first I remove the connection of the built-in chunky power supply and feed the radio with an excellent linear power supply 13.8VDC with 30A capacity in order to exclude the possibility of bad PSU in the radio.

When I start the PLL alignment procedure I go to 28MHz and set to AM and remove the jumper board between TP1-TP2-TP3 according to the alignment procedure described. Now suddenly I get RX and TX with output power!

If I step down some channels RX diminishes and TX stops working (TX light goes on though). Almost as if PLL goes out of lock.
If I now turn the clarifier all the way to the right the RX starts to come back as well as TX but only if I stay few channels below 28MHz.

Ok, so I start to do the PLL alignment procedure and looked this procedure:
1. http://malzev.tripod.com/cb-funk/rci-2950.htm

as well as
2. the "original one" at http://www.cbtricks.com/radios/rci/rci_ ... ll_adj.htm

and finally this excellent document
3. https://randin.org:8443/Request/Documen ... 20Mods.pdf page 153 and page 154

When following the first one above I have no problem setting voltage at J13 to 2.2VDC but I just can't get the 1.2V voltage at pin 3 IC7 to be 1.2V. Either it's jumping around below 1V or as it is now jumping around between 6-7 Volts. Connecting my scope x10 probe to pin 3 IC7 I see a jittering square wave between 0 to 6/7 VDC. It almost looks like 2 square waves at the same time.
(Waveform in next post due to the limitation of max 3 attachments per post.)


When following the 2nd and 3rd procedure and connecting freq counter (HP53131A) via an 10pF ceramic cap to L61 I can not get a reading at all. It is as if as the signal level here is just too low?

After reading through this interesting thread http://www.worldwidedx.com/threads/2950 ... 60.140737/ I decided to start removing some of the wax around the PLL chip IC7 to remove the electrolytics in that area in order to check all of them.

They do indeed look awful:
CRT Hercule Turbo - Electrolytic caps in PLL area - Removed C111 and C157.jpg
and there are residuals on the board as well or is this something else:
CRT Hercule Turbo - Electrolytic caps in PLL area - Removed C111, C96 and C157 - Component side view.jpg
However, when I check all those caps with my ESR meter I get the following readings:
220 uF shows 235 uF with 0.36 ohm ESR
220 uF shows 228 uF with 0.72 ohm ESR
220 uF shows 241 uF with 0.20 ohm ESR
110 uF shows 102 uF with 0.66 ohm ESR
50 uF shows 51 uF with 1.10 ohm ESR
so all the caps seems to be within spec for the capacitance but I am unsure if the ESR values or ok?


So in order to trying to close up this long initial email ( :oops: ), I now need some initial help to get the PLL area going after I have replaced the electrolytic caps in this area. My questions (before caps has been replace) are:

1. Supply voltage on pin 5 IC7 is high? I read 7.8VDC there.
2. Supply voltage on output pin on regulator IC4 7805 is +5VDC so that is ok. What is causing the voltage to be so much higher on pin 5 IC7 then? The zener diode D64? I see same 7.8VDC supply voltage on the second PLL on pin 5 IC5.
3. Can the jittering on pin 3 IC7 be caused by bad varactor diode D66? If yes, can I replace it with BB809?
4. Turning L21 has no effect on waveform on pin 3 IC7.
5. Should I also remove the tantal caps C160, C161 and C156? Is it common that tantals need to be replaced in the same way as electrolytics?
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Last edited by CrazyFin on 08 Dec 2017, 11:39, edited 2 times in total.

CrazyFin
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Re: CRT Hercule Turbo - EPT295013Z - Can not tune PLL voltages

Post by CrazyFin » 08 Dec 2017, 10:45

Scope pattern from pin 3 on IC7:
CRT Hercule Turbo - IC7 pin 3 - Strange jittering square wave.jpg

Scope pattern from pin 3 on IC5:
CRT Hercule Turbo - IC5 pin 3 - Spikes every 10kHz.jpg

Same pattern from pin 3 on IC5 but with lower time frame:
CRT Hercule Turbo - IC5 pin 3 - Spikes every 10kHz - 2.jpg

I am not sure if these two look ok. Signal on pin 3 on IC7 (the first one above) definitely doesn't look good.
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Re: CRT Hercule Turbo - EPT295013Z - Can not tune PLL voltages

Post by CrazyFin » 11 Dec 2017, 11:40

Alright, after spending several hours during the weekend with replacing 6 caps in the PLL section and resoldering all soldering points on half of the board I am actually "halfway" up and running.

Now pin 3 on IC 7 has a similar scope pattern as signal on pin 3 on IC5 so PLL loop seems to lock properly now.
I am also able to get 1.2VDC at pin 3 on IC 7.

Before replacing caps and resoldering solder points I could hear the receive become silently sometimes when I was probing around on the main board with my scope and freq counter but when I pushed with my finger on the back of the board in the PLL area the noise came back and that is when I decided to go over all the solder points in that are so it must have been a cold soldering point somewhere since that part seems to be working fine now.

During my PLL tuning I can not get the freq counter to measure a freq at L61 (which is connected to L4 and Q6): This is the connection point according to most service manuals for RCI-2950/2970 and Galaxy Saturn Turbo as well as CRT Hercule Turbo that I have found. I do get a reading at pin 1 of IC11 and can tune to 10.240MHz there.

I also had trouble with doing the USB/LSB TX OSC alignment where most service manuals says "Connect freq counter to cathode D45" which is the same point where I tune AM TX OSC as well. So AM TX OSC tuning is no problem to get at 10.6950MHz +/- 10Hz but when I move into USB or LSB mode I do not get any reading when TX:ing. Then I found in another older service manual (CRT Hercule Turbo service manual) where it stated that I should short collector and emitter of Q30 and then I was able to do the tune up of USB TX osc and LSB TX osc to 10.6925MHz +/- 10Hz and 10.6975MHz +/-10Hz.

So as it is now, it looks like PLL is tuned ok and I went over to start tuning the TX section.

I put back the small circuit board between TP1, TP2 and TP3 and connected to my dummy load that has an -40dB RF tap where I have connected my spectrum analyzer, scope and power meter (Telepost LP-700). Pressed TX to check that if I get readings on all my instruments and after few seconds a smaaaaall amount of smoke came from RF amp... Shiiiiit! :o

Ok, so I disconnected power from the RF amp and tried to tune the TX section first without the external RF amp and it seems that I am almost there with that. Opened up the RF amp and directly saw a blown electrolytic cap:
CRT Hercule Turbo - Blown el-cap in the PA.JPG

When I removed the RF amp board from the heat sink in order to replace the cap I found this HORRIBLE amount of heat sink paste under the transistors and why have the chunked in that huge amount of heat sink paste on the two diodes?!
CRT Hercule Turbo - RF amp - huge amounts of heat sink paste.jpg

I cleaned up the RF amp board, replaced the cap and put some new heat sink paste on the two transistors (normal amounts).
Mounted back the RF amp board to the heat sink and the RF amp was alive again. :)

Do any one of you know what the trimpot R901 on the RF amp board is used for? Is it for setting the level of RF signal from the mainboard final transistor where the relay for the RF amp kicks in? Here is the partial schematic for the RF amp board:
Ranger RC-2970 - Schematics - partial showing RF amp.JPG

I will report back in few days with the results from TX tuning. After a while I was able to tune in TX quite ok but I have some questions (need to go over my notes first... :geek: ).
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Re: CRT Hercule Turbo - EPT295013Z - Can not tune PLL voltages

Post by CrazyFin » 14 Dec 2017, 08:55

Ok I have been told that R901 is for setting the zero-drive idle current for the linear transistors on the RF amp board (EPA010010A)

Suggested method is to remove the red wire that goes from amp board to mainboard near the driver and final transistor. Measure the current running through here and measure it in USB or LSB mode with mic gain at zero. Push the PTT and set trimpot for minimum current. This reading will now show the relay's coil current. Then turn up the trimpot to get 100mA higher reading. Idle current for the RF amp board is now properly set!

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Re: CRT Hercule Turbo - EPT295013Z - Can not tune PLL voltages

Post by cb4ever104 » 14 Dec 2017, 10:34

Well , you seem to be doing alright by yourself . The reason why I dislike these models it due to this feature . I'd much rather have the base model with 2 x 1969 outputs and an external amp .

Sammy
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Handle "Fortune Hunter" back in the "day"
Radios ..... anything that says "TAIWAN R.O.C" on the back.

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Re: CRT Hercule Turbo - EPT295013Z - Can not tune PLL voltages

Post by CrazyFin » 14 Dec 2017, 11:00

I dont either like these models with an extra amp hanging on the back.

Well, I am not doing too good by myself... :oops: I wish I had more experience but I keep learning by reading a lot and testing a lot. :geek:
Trying to understand by reading a lot of docs on the web but sometimes the procedures (even for the same mainboard) are slightly different depending on what the name on the front is... :crazy:

For example when aligning the PLL area most service procedures for the EPT295013Z says that I should connect freq counter to L61. L61 is right to L4 nad Q8 which both are located quite "far away" from the PLL section on the schematics (on the upper parts). However, I do not get any reading at all there. Almost as if there is no signal there or the level is just too low. When I connect to pin 1 on IC11 then I can adjust VC1 properly to steady 10.240MHz +/-10Hz.
When I turn L4 I am able to get reading on the "secondary" side of L4 (not the side where L61 is connected) but then it screws up other parts in the PLL area so I have for now on tuned it by connecting scope and freq counter to pin 1 on IC11 and tuned there.

As for now I am currently struggling with some remaining issues:
1. Can not get enough modulation percentage when I keep AM dead key at proper level and ALC setting and bias setting correct. I am hovering around 70/75% in AM mode. When going into SSB the modulation percentage gets even lower (around 60/50%). I have not replaced any caps in the audio area yet (except for the one that was blown as I posted in the first post).

2. I seem to have some kind of oscillation during the first 50ms to 500ms where I can see on the scope and modulation meter that I reach 100/120% modulation and then it snaps back to that low level again. I will try to capture this on my scope and put a link to the video here.

3. I´ve been able to reduce the harmonics quite ok when looking at the spectrum analyzer but I am not happy enough. When I do the tuning without the ext amp then it is quite fine but of course the extra amp just amplifies the harmonics so much that the two I see most of (2nd and 3rd) just pops up like crazy when running on the ext amp. I´ll post some spectrum pics of that as well. Splatter is small though and the bandwidth usage around the carrier level looks clean (as far as I think at least... ).


By the way, do you agree on that the amount of heat sink compound that was used as shown in the pics above was just way too much and why have the put such amounts of that compound on the diodes as well? :shock:

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Re: CRT Hercule Turbo - EPT295013Z - Can not tune PLL voltages

Post by black olive » 14 Dec 2017, 13:51

cant help with the VCO but the diodes are part of the transistor biasing circuit and need thermally linking to the transistors. as the transistors warm up and drift, the diodes drift the other way and keep the bias stable. the way they are mounted eg not in close physical contact to the transistor means that the big blob of thermally conductive paste has been used from what I can see

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Re: CRT Hercule Turbo - EPT295013Z - Can not tune PLL voltages

Post by CrazyFin » 14 Dec 2017, 14:33

black olive wrote:
14 Dec 2017, 13:51
...the diodes are part of the transistor biasing circuit and need thermally linking to the transistors. as the transistors warm up and drift, the diodes drift the other way and keep the bias stable.
Aaahhh so they have the same functionality as the diodes that I've seen on many drivers and finals like this:
CRT Hercule Turbo - diodes mounted on top of final and driver transistor.JPG
Then I understand the reason by the HUGE blob of thermal paste but I've always been thinking that when using tooooo much thermal paste it actually defeats its functionality of transferring heat efficiently.
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Re: CRT Hercule Turbo - EPT295013Z - Can not tune PLL voltages

Post by black olive » 14 Dec 2017, 15:09

yes, it looks like theyve worked on the more is more principle

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