Alan 88s Cybernet PCMA001S card

[spiderman]

Greetings to everyone, I have an Alan 88s cb radio with Cybernet PCMA001S card. the Q30 2SD1192 burnt, and also the R184 of which it is no longer possible to read the value, someone can help me, and tell me what value is the R184 resistor?

[SiriusHardware]

Hello Spiderman. The PCMA001S chassis is familiar to a few of us here but not really in ALAN branded radios as that brand was most popular in Italy as far as I understand it.

You can find a representative circuit for a radio using a PCMA001S chassis here:

http://www.zen96216.zen.co.uk/cb/sch...m-pcma001s.htm

This may not be exactly identical to yours, yours may have more features or less features than the one in the diagram.

Q30 is the regulator / modulator which supplies power to the transmitter output stage in some modes and if that has burned up this could be down to problems with the RF output transistor (Q8) or driver transistor (Q7) or both, so check that they have not gone short circuit from collector to emitter before replacing Q30.

R184 is rather hard to find on the diagram, it could be the one indicated here on this section (attached) from the diagram and if it is that one, connected at one end to the 'TU' (Tune) terminal on the PCB then it looks like it is 390R.

However it is hard to see how that resistor could ever have enough current passed through it to burn it up, unless someone has made a wiring error at some point, so check the wiring especially around the +/- tune control to see if anyone has been trying to modify it.

[spiderman]

Thank you so much Sirius Hardware for your advice, the Q7, and Q8 are good, the Q30 which has been replaced with a BD707 which is not equivalent to the original 2sd1192 "" the BD707 is not a darlington "", also the R184 and of 10 ohm 3 watts the wattage and the value seemed wrong to me, so I asked for the exact value of the R184, all this causes a decrease in output power to less than 1 watt. Today I can replace the Q30 and the R184 and see what happens. The radio cb comes from Italy.

[SiriusHardware]

In that case I think R184 can not be the resistor I pointed out in #2.

Yes, Q30 does need to be a Darlington as they have very much higher gain than a 'normal' transistor. If a Darlington was there originally, it must be replaced with a Darlington.

[SiriusHardware]

I have searched the diagram again and I still can not find another candidate for R184. The resistor you believe is R184, does that have one end directly connected to the 'TU' terminal on the main PCB?

[spiderman]

I don't know if the BD707 or the 2SD1192 was originally mounted, on all the diagrams that I managed to download the Q30 2SD1192 - 2SB837 is shown. This radio has been on the shelf down in the basement for many years.

[spiderman]

In this excellent site "" https://www.rogerk.net/forum/index.php?topic=73951.0 "", the photos of an Alan 88s are published I have looked good but the 3 watt resistance in front of the Q30 does not there is' .

[SiriusHardware]

on all the diagrams that I managed to download the Q30 2SD1192 - 2SB837

I think you mean 2SD837 for the second part number, as 2SB... always indicates a PNP type transistor.

Can you please show us two good clear photos of your R184 location, one with the part at the centre of the picture and maybe 4cm of area around it, and the other a much closer shot of the location of R184 with just a few components surrounding it.

Edit: sorry - as a new forum member your first few posts are moderated before being posted so I did not see your post #3 with the photo until now. That big resistor does not seem likely to be original but I do not think it can be the resistor I pointed to in the section attached to #2, therefore the previous suggestion of 390R for the value is probably not correct.

[spiderman]

OK sending photos, the R184 is connected between the emitter and the collector of Q30.

yes exactly I meant 2SD837

[SiriusHardware]

Sorry, so far you have been saying R184 for the resistor part number. Do you really mean R814? I don't think the resistor numbers go so high. Edit: I see you have corrected this to R184.

This is a problem as the PCMA001S diagram we have does not show any resistor directly across C-E of Q30. Maybe someone has a diagram for another radio using this chassis, maybe even for the Alan 88 itself.

Cybernet were quite good that way, the radio owner's manual usually had the specific circuit diagram for the radio model on the inside rear page.

If or when you remove the big resistor I would be interested to see the area immediately in front of Q30 without the resistor in the way so we can read what is printed on the PCB.

[spiderman]

sorry I got confused, the offending resistance is the R184.

[spiderman]

I send the photo of the location of R184.

[SiriusHardware]

Here is a specific circuit for the Alan 88S - unfortunately less good quality than the one linked to earlier.

http://www.cbmania.ro/image/data/Blo...-alan-88-s.pdf

Even on this version of the diagram which is specific to the Alan 88S I do not see a resistor between Q30 C-E, I wonder if there was originally no resistor fitted in the R184 position and someone has decided to fit one, for reasons unknown.

You can see another unpopulated position for a resistor, R188, further up in your last image. If you look at the more fully featured radio diagram linked to in #2, R188 is present, but in the diagram for the Alan 88S, R188 is not present and R188 is also absent from your radio. I think that R184 is not supposed to be fitted in your radio either.

The correct diagram for your radio is useful because it shows us that power to the RF driver and RF power transistors is supplied by Q30 emitter in both AM and FM TX modes, whereas in USB mode and LSB mode Q30 is bypassed and the supply to the RF driver transistor and RF power transistors is taken directly from 13.8V. In some other radio variants which also use this chassis, the RF output stage is only powered from Q30 in AM mode.

So, you have a correct Darlington NPN replacement for Q30 and you think that Q7 and Q8 are OK, what happens if you fit your replacement Q30 and leave out R184?

[spiderman]

This is exactly what I will do tomorrow, I mount the Darlington without the R184 and let's see what happens.

[SiriusHardware]

Meanwhile, maybe you can ask on the Italian forum if other Alan 88S owners can look to see what is (or is not) fitted in the R184 position on their PCB. (As ALAN is primarily an Italian marque or brand, you are more likely to find other owners of this set in Italian forums).

Here in the UK we do have some basic CB radios with the ALAN brand on but at the same time also the 'Midland' brand, they date mainly from the late 1980s onwards so it seems ALAN took over the Midland CB brand name at some time.

[spiderman]

Hello to all of you, I was unwell for this reason I have not written anything anymore, I replaced the Q30 BD707 instead of the original 2SD1192 I mounted a BD645, I tried with the R184 resistor connected and with the R184 resistor disconnected, but power does not want to increase.

[SiriusHardware]

Hello Spiderman, sorry I missed this reply until now.

If you put the unit into SSB mode and apply a strong audio signal (like a whistle) to the microphone, is the RF output power still very small?

I ask this because power to the output stage is only controlled by the Darlington (Q30) in FM and AM modes. In SSB mode the mode switch sends 13.8V power directly to the output stage, bypassing Q30.

If you also have low output in USB and LSB mode this would indicate some other problem with the transmitter, not related to the Darlington.