Looking for an RF coil for Galaxy DX 2527 (RCI 2950)

[OldTech03]

Just seen this if memory serves me Q38 supplies bias voltage to the dual final section while the driver gets it from the mirror board. There are 2 150 ohm resistors that tie into the bias voltage feed from that transistor it would be quick and easy to check and make sure you have voltage up to those resistors I want to say from memory they are like R255,256 or 257 at any rate if you don't have voltage on both sides of those feeds then it's just a matter of following the yellow brick road.

 

[OldTech03]

Hey, Andy did you happen to see anything crazy about that schematic with reference to the 2312's?

 

[Handy Andy]

Yes, I noticed it too...and CBT called it "New"

And as far as I can tell - its; correct - D90 bias diodes' banded end goes to ground


So hopefully it's puts together right - because the original photo he sent is what I'm using to demonstrate...



Oh, those good old days...we're having them right now...

(GOSH DARN IT - I sound like a "Fridays" ad...)
:+> Andy <+:

 

[OldTech03]

Well, the schematic proofreaders where sleeping for sure. I kept looking at the emitters and collectors being swapped and wondered how many newbies might have been trying to make sense of it? Ok back to work.
Oldtech03

 

[Handy Andy]

The above is a good example of photos and how they can save your butt.

And is why I can't post photos of issues with customer radios.

But you can use them to "rebuild" an area and need to locate where this and that went - even to the point of locating and reseating slugs to the right position to recreate the original problem to fix that once the radios' got a heartbeat. At least you can re-align as needed.

Because you never know who else had been in there - NOS doesn't mean they never took it out of the box or even had the covers off so they can be used for side by side comparisons and the customer chose something else. The unchosen one left on the bench goes back into storage - so it got thrown back in the box with all the smidges and skin oils ready to eat away at the finish while its' being stored somewhere damp until it sees the light of day again.

I'd rather give the customer the benefit of the doubt and show any before and after as needed to ease their minds that the problems are resolved. In most cases - the problem was not theirs - but something from either accidents or acts of god, lightning, power surges - stuff that makes the radio fail but if its' repairable - even insurance can pay for the repairs thru reimbursements if its' packaged with the comprehensive claims as repairs and expenses.

So PoDuck, my hats off to you for those pics, because even though this may be an error - it could have turned out a far worse outcome.

I hope it's something simple.

I caught hell for this before...

 

[Handy Andy]

Well, the schematic proofreaders where sleeping for sure. I kept looking at the emitters and collectors being swapped and wondered how many newbies might have been trying to make sense of it? Ok back to work.
Oldtech03

Yes, and I went back this morning and updated that graphic.

I can't do anything about the original - it's there on the site for everyone to look at and demonstrates someone fell asleep at the switch.

But this sites' got the updated graphic per your memo on this...

 

[PoDuck]

Thanks Andy,

Tap - test ohmic result from the Prong that goes to the Finals - to this tuning tank core. If it's open - you may have a blown trace of a component failure.

I think I understand this, but I might be wrong. Do you mean test basically between TP2 and the collector of Q46? If so, I get 0.2 ohms. So, the trace is good.

As for the rest, I get 4.02 volts on TP3 in AM mode, which obviously means I get continuity from the regulator to the test point. It's a bit lower than 5 volts, but looking at the voltage chart, that's pretty close to what I would expect the voltage to be coming from that leg.

I'm still stuck on the fact that it was at least putting out 6 watts before I pulled the finals out and tested them. When I put them back in, they don't work. Nothing made noise, and I saw no magic smoke. Just things don't work. These finals each have a diode and a capacitor, and I considered that they may not have been put in properly, or that something got bridged that I couldn't see, so I cleaned up all the solder off the board, ensured that the parts were sitting in the right place, and resoldered everything, and still no TX power.

Let me know if I didn't do that correctly.

 

[PoDuck]

Just seen this if memory serves me Q38 supplies bias voltage to the dual final section while the driver gets it from the mirror board. There are 2 150 ohm resistors that tie into the bias voltage feed from that transistor it would be quick and easy to check and make sure you have voltage up to those resistors I want to say from memory they are like R255,256 or 257 at any rate if you don't have voltage on both sides of those feeds then it's just a matter of following the yellow brick road.

Well, I am getting no voltage on RX and on TX I get 0.866 volts on R255, and 8.61 volts on R256 and R257, although only R255 and R257 are 150 ohm, while R256 is only 18 ohm.

 

[PoDuck]

So PoDuck, my hats off to you for those pics, because even though this may be an error - it could have turned out a far worse outcome.

I take pictures all the time for things that I may have trouble getting back together properly. For instance, I took pictures of the bottom side to see where the capacitors were mounted across those finals as well.



Also, I looked at the board layout view on CBTricks, and it shows the diodes. The copper side parts layout view shows the capacitors. When I started having this trouble, I double checked with those to see if maybe I had attached the diodes and caps wrong.

 

[Low_Boy]

This is a stupid question but may you have the final where the driver should be and viseversa?

 

[Handy Andy]

When you pulled the finals, did you check their numbers? Were they 2321's or 1969's?

We saw diodes on the original (they're like the MV-1Y) - a "varistor" used for bias - it was a diode but the mounting was designed for thermal contact and profiled the part it was supposed to keep in proper class of operation.

WHOAH!...(Found more attached before I could edit this...)


So, that makes me wonder, if the Bias Diodes are sucking the life out of the Base region - they are supposed to ISOLATED - usually thru a Ferrite Bead (I use a Bead and 2.2 ohm if I go back into these things) to "buffer" the voltages and RF currents from "re-rectifying" within the bias circuit can cause some transistors to "crowbar on" like a switch and blow quicker than you can turn off the power. Self-oscillation is what I'm talking about - turn the bias up too high in mA - and the parts turn on and unless loaded - which these are not - just for RF - they make very efficient switches and blow like fuses...



Place a dummy load on the Antenna jack...so the rest of this will be the test...

So when checking - you pull the test jumper that shorts all three - use TP 3 as POSITIVE (Red) and TP1 as NEGATIVE - you adjust the DRIVER bias by setting the DVM to Amps, usually 200mA or 2A - so you can trim the bias drain current - this current flows all the time the radios TX's - so it can supply the base leads a working small trickle voltage (usually about 0.65VDC) all the time it's in TX mode - this method forms it's class of operation - in this case Class AB - VR11 trims this Driver bias current - set it to about 45mA...lower than recommended is the safety margin in this radio - too high - you latch it and poof...

For the Finals, it's a little more tricky...

I' recommend that you pull those 150 ohm resistors and replace them with 180 ohm 1 watt types right now before things go any further. The 18 ohm resistors used are fine but the Diodes are shorting to ground some heavier current that reaches closer to the max forward current ratings when these are placed in SSB mode. If the 150 ohm resistors drift - they'll drift thermally - lower in resistance. This can put the ratio of 150 / 18 a bit lower and force the diodes into a runaway condition and may not continue to work properly in all modes - including FM modes - because the thermal profile talked about earlier - is affecting - stressing all parts involved. R255 and R256 are the ones I switch to 180 ohm 1 watt...

I see some things in your latest post - help me and make sure they aren't shorting out something they shouldn't - because if one finals' base shorts - the section can't get power to fire up the other final...

 

[PoDuck]

This is a stupid question but may you have the final where the driver should be and viseversa?

Don't worry about asking "stupid" questions. After all, there are people that forget to turn the power on when they call tech support.

I did them separately, and just to be sure, I just counted my remaining 2312's and there are 8, while I have 9 2166's left. I started out with 10 of each. I really don't want to pull them out again to check, but I'm 99% sure I used the right ones.

 

[Low_Boy]

Are the finals from a known good source? 2312 transistors are quite rare.

 

[OldTech03]

Well, I am getting no voltage on RX and on TX I get 0.866 volts on R255, and 8.61 volts on R256 and R257, although only R255 and R257 are 150 ohm, while R256 is only 18 ohm.

Ok, there should be the same voltage readings "small difference" across both 255 and 257 they are essentially what provides the bias voltage to the finals. Another word if you see 8.61 volts on 255 you should also see 8.61 on 257 that would be the feed side so to speak and should see the same level whatever it may be on the other side of either resistor.

 

[PoDuck]

When you pulled the finals, did you check their numbers? Were they 2321's or 1969's?

They are 2321's.

As for where you think there might be a short, that picture was taken before I did anything. I have since removed all the solder, cleaned the board, resoldered everything, and cleaned off all the residue again. It looks quite different now, and I laid the caps over so I could see things when I replaced them.

As for replacing the resistors, first of all, R256 is 18 ohm, not 150 ohm. It is R255 and R257 that are 150 ohm. Second, in my 1 watt resistors, I have 150 ohm, and 200 ohm. I don't have 180 ohm. Would either of those be better?