Dutch RF - 6w DRFS06

[LAZY]

Hi all, I've now wound all the coils,which turned out to be quite tricky for a first timer. But I now seem to have made an error somewhere, which has resulted in a bit of smoke and a bang (pop really).





Now i've uploaded the pictures I see that i've soldeded 2x of the pointometers incorrectly (power and Volume) So I will have to remove and re-solder in the correct place. But I also I forgot to turn the power pointometer all the way down, meaning the middle leg wasn't to ground.

I did the first test to check the 5.1v regulation earlier on in the building guide, which should stop any damage of the PLL ic and processor by testing pin 4 of the processor socket and all was good 5.3v.

But now i've come to testing the PLL I can see C5, the 220UF 16V RADIAL ELECTROLYTIC has gone pop as the bottom of it has come out.

Which other components have I probably ruined?

Any comments / advise appreciated.

Lazy.

[pjeva]

As we told you before, trimmer potentiometers are fine. Orientation doesn't matter. Regarding capacitor, this unit is supplied with 12-15v so you should use 25v capacitor. 16v one must be expensive one to hold this supply voltage. This one on your board is not exactly high quality one. I can also tell that you didn't solder output transistor. Without it, driver transistor has open end on its output so it suffers maximum swr and it can draw too much current (due to its bias) and burn.

[LAZY]

Thanks Pjeva. This is strange as the guide says about testing the Control PLL & Oscilator before adding the final, and shows a picture of this!



The below has been translated via Google Translate.

"Control PLL & Oscillator We are now so far that we can test the oscillator and PLL . This may be connected with or without display. Turn the power potentiometer fully counterclockwise . Verify that the middle leg of the power potentiometer to ground (-) is . If there is an external potentiometer is used for the power control than the center pin to connect temporarily to ground. Connect a supply voltage of 12,5Volt to the plus and minus."

"If all goes well , it will lock LED after a few seconds. The default preset frequency is tuned . One can easily check that a frequency counter or FM tuner." I though I would be able to tune into a signal with without the final being fitted.

"The control voltage may be measured at one of the two inductors , and will amount to approximately 2 volts. This voltage may vary slightly by variation of the oscillator coil , but this is no objection."

"By turning the trimmer , the oscillator can be put right on frequency."

AFTER ALL OF THE ABOVE IT SAYS ABOUT FITTING THE FINAL!!!!

I'll solder the final and attach a dummy load before I test it again!
Like you say the 16v Cap is supplied in the kit, I'll order a 25v one and replace it. Do you think i've blown/burned the driver transistor too? (Is this the SGA6489 or MSA0886?), Anything else you think i may have screwed up in the process?

Thanks for the help. Lazy.

[Shedbuilt]

Probably the most common reason for electrolytic capacitors to do this, is reversal. Is it possible you inserted and soldered the capacitor the wrong way round ?
Hopefully you didn't reverse the supply wires to the board.
As you've followed the instructions, hopefully running without the final, won't in itself have blown the driver. To know what other damage may have occurred, you really need to know what caused the capacitor to vent. If it was just reversal of the cap itself, it probably won't have caused any other damage.
Was the board doing anything when powered up ?

[teckniqs]

I agree, a 16v cap should always be fine with 12-15v unless it's faulty or in reverse polarity.

[pjeva]

I agree, a 16v cap should always be fine with 12-15v unless it's faulty or in reverse polarity.

Thats what i mean..faulty or bad quality, dead-on-arrival... seller could not know that. He put it in the right way as we can see on the pictures of empty and filled board. So it leaves us with faulty capacitor or bad supply polarity, later will destroy pll chip, display and microcontroller. Everything else should be fine.
Lazy, replace this cap, check supply polarity and try to use like 8v in supply and don't put final fet yet. Turn it on and check if display lights up and shows reasonable characters (like frequency). This will eliminate faults in microcontroller and display. If it locks to frequency, pll chip should be fine too. if it doesn't lock, try to change frequency to lower or higher one and look if varicap voltage changes. If there is no voltage on varicaps or it doesnt change with change of frequency, probably it is damaged pll chip.

Practice makes it perfect

[Gum]

Turn the power potentiometer fully counterclockwise . Verify that the middle leg of the power potentiometer to ground (-) is . If there is an external potentiometer is used for the power control than the center pin to connect temporarily to ground. Connect a supply voltage of 12,5Volt to the plus and minus.

Which way did you turn the power pot?

If you mounted the presets the opposite way round, turning them anti-clockwise would have the opposite effect...

[Shedbuilt]

He put it in the right way as we can see on the pictures of empty and filled board.

Yes. Well spotted. I forgot there was an unpopulated picture at the top. The cap definitely appears to be the right way round. I also found a PCB track layout on the Dutch RF shop site, which also supports this. C5 appears to be directly across the main supply rail. Hopefully just an issue with the capacitor itself. The board doesn't seem to have any reverse supply protection, so reversal of +ve and -ve, would be expected to cause widespread and extensive damage.

Just found the schematic in the documentation zip file too.

If you mounted the presets the opposite way round, turning them anti-clockwise would have the opposite effect...

I'm not familiar with these pots, but if the three pins are in a line, with the wiper in the middle, then this is also true. If fully counter-clockwise is normally minimum voltage, then reversing the orientation of the pot, will make fully clockwise the minimum voltage setting. Fully counter-clockwise would take the gate voltage up to 6.2v from zener D1...
This will not affect C5 in any way, but still something to either rectify, or at least be aware of. It's ok during initial setup, when setting the gate voltage with a meter - before inserting the FET, but might be forgotten later, if adjustments are done on the fly, so probably better corrected.

EDIT: The penny drops !!
The bias pot is correctly orientated. Volume is upside down, but the pots themselves are transposed. The 5k pot for "Volume" is in the position for the Bias pot, and the 10k pot for "Bias" is installed in the position for the volume pot. This should be corrected, but again, wouldn't stop it from working fairly normally. Having the 5k pot in bias position, will prevent you achieving 6.2v across the zener (from 12 ish volt supply), but you should easily get enough bias - albeit unregulated.......

[Shedbuilt]

EDIT: The penny drops !!
The bias pot is correctly orientated. Volume is upside down, but the pots themselves are transposed. The 5k pot for "Volume" is in the position for the Bias pot, and the 10k pot for "Bias" is installed in the position for the volume pot. This should be corrected, but again, wouldn't stop it from working fairly normally. Having the 5k pot in bias position, will prevent you achieving 6.2v across the zener (from 12 ish volt supply), but you should easily get enough bias - albeit unregulated.......

Sorry. Still got that slightly wrong. The bias pot is upside down. The other two pots are the right way up, but the power pot is the one swapped with the volume pot. Bias pot appears to be 10K as it should be. Power pot and Bias pot should be 10K (103). Volume / deviation pot should be 5K (502).
Pretty sure "Lazy" is aware of this, and as above, it's definitely not related to the exploding C5.

[LAZY]

Thank you for all your comments and suggestions people. As soon as the Solder Sucker Pump and the new Cap i've ordered arrive i'll give your suggestions a try. I'm hoping it was a bad cap and not me giving it the wrong supply polarity!

To be continued........

Lazy

[Shedbuilt]

Hi "Lazy", C5 is a decoupling cap, primarily for the output stage - to help safeguard against possible low frequency nasties. It's in parallel with a couple of ceramic caps, which decouple the output stage at higher frequencies. There don't appear to be any three legged regulators, and the previous stage has its own decoupling - including a 100uF electrolytic. As long as C5 hasn't gone short circuit (which it hasn't if you're getting ~5v on the 5v supplies), the issues with the cap, won't stop the circuit from working. With the final FET disconnected, in my opinion, C5 isn't really doing much. If the board is doing anything when you power up, I would say it's safe to try the steps which pjeva mentioned (does the display light up, display any info etc, voltage checks on the varicap voltage; see if it changes when you try and tune up) etc. If you have access to a frequency counter or a wavemeter, you could try to pick up from the oscillator tank circuit, to see if it is oscillating anywhere (or try to pick up with a radio close to the oscillator).
The pessimist in me says that; if you have a cap which blew up, and you're not certain that you didn't reverse the power rails, you almost certainly did. If you did reverse the rails, even momentarily, you've probably blown most of the semiconductors. The stuff which is only on the 5v rails, "may" have survived; by virtue of the zener diodes acting as a shunt, and limiting the reverse voltage to about -0.7v.......
When you do power it up again, if you can, watch the current consumption, check all the lower voltage supply rails with a voltmeter, and watch for smoke. If there's a chance it was reversed, there could be components which have gone short circuit.

[LAZY]

Hi All. It lives! (well sort of).

I can confirm I did reverse the supply polarity! As suggested I connected the board to a lower supply voltage (the correct polarity), and the LCD lit up. I realised the LED was installed the wrong way round and have rectified this.
To my suprise the LED came on, and can confirm I have a carrier on 98mhz, although nothing showing on the LCD screen it was just lit up.
When I try to set the frequency to something else the LCD and the LED flashes and displays a character and it won't lock. Although I can set it back to 98mhz and it locks again.

As suggested I would like to check the Varicap voltages. I've looked at the components list and can see 4x (2 x BB809 Varicap D4, D9 & 2 x BB809 Varicap D7, D8) which of these do I need to check and what voltage should I see?

In the guide at the point where I F*"ked up, it says to check the voltage at 2x points
"The control voltage may be measured at one of the two inductors, and will amount to approximately 2 volts. This voltage may vary slightly by variation of the oscillator coil, but this is no objection." see pictures below.


Here I am getting nearly 6v where I should be getting 2v.


Unfortunatley I don't remember what voltage I was getting here, but was more than it should have been. (will update when I get home)

Is it possible i've mullered the PIC16F628 or TSA5511.

Can you recomend any further tests/advise.

Lazy.

[Shedbuilt]

Hi All. It lives! (well sort of).

I can confirm I did reverse the supply polarity! As suggested I connected the board to a lower supply voltage (the correct polarity), and the LCD lit up. I realised the LED was installed the wrong way round and have rectified this.
To my suprise the LED came on, and can confirm I have a carrier on 98mhz, although nothing showing on the LCD screen it was just lit up.
When I try to set the frequency to something else the LCD and the LED flashes and displays a character and it won't lock. Although I can set it back to 98mhz and it locks again.

As suggested I would like to check the Varicap voltages. I've looked at the components list and can see 4x (2 x BB809 Varicap D4, D9 & 2 x BB809 Varicap D7, D8) which of these do I need to check and what voltage should I see?

In the guide at the point where I F*"ked up, it says to check the voltage at 2x points
"The control voltage may be measured at one of the two inductors, and will amount to approximately 2 volts. This voltage may vary slightly by variation of the oscillator coil, but this is no objection." see pictures below.


Here I am getting nearly 6v where I should be getting 2v.


Unfortunatley I don't remember what voltage I was getting here, but was more than it should have been. (will update when I get home)

Is it possible i've mullered the PIC16F628 or TSA5511.

Can you recomend any further tests/advise.

Lazy.

The varicap control voltage, is the voltage which you are measuring at the inductors, L13 / L14.
If you were still running on reduced voltage, it could be that the 5V rails are not reaching 5V (if you are down to 8V, I think that's likely, looking at the circuit). It looks like Zener Diode, ZD2, regulates the 5V rail. R13 and R24 in parallel, feed this from the main +ve rail; 220R/2 giving 110R. At the stated 66mA, 110R would drop over 7V, so the Zener voltage will only ever be reached from over 12V (in practise, current will probably be less at lower voltage, but it still won't reach 5V from an 8V supply). If so, this may be causing part of the problem. Having come this far, I doubt that you will kill anything which isn't already dead, by increasing to normal supply voltage, but keep an eye on the 5V supply whilst doing it. Maybe increase to 10V supply first, then assuming the 5V supply hasn't gone over 5V, increase to normal (~12.5V), and see if the functionality changes. It sounds (if I read what you described right), like the PLL and PIC are doing something at least; maybe because the Zener crowbar'd the 5V supply (as in earlier post), which sounds hopeful. The oscillator probably survived because it's J-FET based.
In terms of the varicap voltage, increasing voltage will reduce the capacitance of the varicaps, which will increase the frequency, so if you try to tune up the band, you would normally expect the varicap voltage to increase.

[pjeva]

Ok, builtinashed is partially right. It is normal that you have 6v there and lock at 98MHz. If you go full supply, it will anyhow stay at 6v for 98MHz. With 12v, 108MHz would be around 12v and 88 would be at 1.2 v approx. LC oscillator (in this case varicaps and inductor) will resonate only dependent of diode capacitance and inductance of the coil. No matter what voltage you supply to the rest of the circuit. I may say that 6v for lock at 98MHz is perfect. Regarding everything else, looks like that PIC and PLL are fine and survived disaster of capacitor. Display may be damaged. Try now with 12v (and correct polarity ) If display doesnt show anything or shows only dots or squares, it is damaged. There should be contrast setting trimmer pot so try to change it a bit and see what happens...
Cheers!

[Shedbuilt]

LC oscillator (in this case varicaps and inductor) will resonate only dependent of diode capacitance and inductance of the coil. No matter what voltage you supply to the rest of the circuit.

Yes. Where I said "In terms of the varicap voltage, increasing voltage will reduce the capacitance of the varicaps, which will increase the frequency, so if you try to tune up the band, you would normally expect the varicap voltage to increase.", what I meant was that if the tuning up / down function is working, you would expect the varicap voltage to increase when you try to tune up, and decrease when you tune down. Where I talked about the supply voltage possibly being too low, I meant that, with reduced main supply voltage, the 5V rail may be too low for the proper operation of the logic and the display (since at 8V, or even 10V main supply, the 5V supply will not reach 5V).
The VCO looks to be specifically designed for low V/Hz (or high Hz/V), so should need a relatively small varicap voltage swing, but the principle is the same (ie highest varicap voltage at the top end, lowest varicap voltage at the bottom end).
Instructions suggest that tuning voltage should be ~2V at the default frequency, but don't seem to say what the default frequency is - presumably somewhere around the bottom end.
You're right. There does seem to be a contrast control for the display too.

Lazy, going back to one of your posts, the purple or pink trimmer you showed, is not a voltage test-point, nor for adjusting voltage at a test point. It is a (very) fine tune for the frequency. You would only adjust this with reference to a frequency counter - basically, so that if the unit is tuned to 98.0MHz (for example), you fine tune it to read 98.0000(etc) on your frequency counter. It varies the capacitive loading of the crystal, and the adjustment will be too fine to see on a radio.

[LAZY]

Ta Daaaa.......... It lives. C5 Cap replaced, LCD working, and locking across the band.



I've measured the Varicap Voltage across the band and unfortunatley am unable to get it as low as 2v. At 87mhz it's 3v and at 108mhz its 9v. Is this an issue?

I've removed the Power potentiometer from the board and installed the pin headers to use the external potentiometer. I intend to leave the bias pot installed the wrong way round (remembering to turn the oposite direction when setting the bias). With regard to the deviation pot, does it have to have the 5k pot for proper operation, or can I leave the 10k pot there. Because it's been a bugger to remove and re-install components without messing up the pads. Maybe I just need to get better with the solder pump/de-solder braid.

Only other issues so far are the up/down/set buttons. The up and set buttons work, down does nothing. Do they need to be orientated when installed?

With the above in mind, do you think it's safe to install and test the final?

Thanks for all your help guys.

Lazy.

[pjeva]

Nice!!! There you go! Voltage on varicaps is perfect, do not change anything! To achieve voltage from manual, you need to spread coil in oscillator, but do not do it (at least for now). Leave that 10k pot in deviation setting, it would not make much difference. Regarding buttons, they will go into holes any way around but you must check that all three are oriented like two that work. I'm 90% sure you turned one that don't work for 90 degrees. 10% are chances your flat cable for this one button don't conduct.
Hope you will finish it soon. It is now safe to add power
Cheers!

[Gum]

Yes, well done! I ordered the last one from Mauri's site the other day - I'm sure there were 5 or 6 listed in stock when you started this thread... Maybe he'll bung you a free capacitor as commission.

[LAZY]

Hi all, Me again.

Another update:-
Up, Down, and Set buttons now all work!!
I've installed the Final (RD06HVF1) connected a power meter and dummy load. Switched it on and........... the power meter shows 0w.
The guide says to test the bias voltage at the choke and the value should be 5-6v. When I test is shows only millivolts, even after adjusting the bias pot.

Testing the voltage on the RD06HVF1 on the Gate, and Source pins I have 0v and on the drain Pin I have 12v. Is this correct?

I thought I should check the voltage on the SGA-6489 too. I've read that this is an amplifier, not sure but does it amplify ready for the final? On pin 1 (rf in) i'm measuring millivolts and on pin 3 (rf out) i'm reading millivolts too. I was expecting a larger figure.

Can you please advise where to go from here? Feels like i'm really close to having this fully working.

Thanks. Lazy

[pjeva]

Sga surely don't work on milivolts. Try to turn bias pot other way around few turns and check what happens. 5-6v on gate is too much. Do not go over 3v. I think that same pot controlls bias and sga voltage but i am not sure as i dont have schematics near me. Check again connections between sga and power supply and gate of rd06 and sga