14th Dec 2018, 2:29 pm | #241 | |
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Re: Cybernet PTBM121D4X problems
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L15 is (as Techman pointed out) in the DC supply path to the output stage rather than the RF chain. I think the most likely circumstance for that to be damaged is if either the output or driver goes s/c collector-emitter, which in this case they appear not to have. No telling, though, what has happened to any transistors originally fitted to the set in the past and what damage could have occurred. John, not sure if this is correct but if the leads of the driver and output are already unsoldered and straightened out, you may be able to lift the whole rectangular heatsink 'cage' off the PCB if you remove the four fixing screws which you can see on the green side of the PCB - there may possibly be other screws fixing the cage to the side of the chassis as well, I can't remember. If you can, if makes it easier to fix the transistors in place with the cage out of the set and then lower it into the PCB, carefully feeding the transistor leads through the appropriate holes, bolt it back into place and then solder the transistor leads. Although the transistors seem OK, should we rule them out by trying the transistors from the scrapper in it to see if anything changes? If the behaviour is exactly the same with an alternative driver / output pair in then that would make it fairly certain the fault lay elsewhere. (If we were spectacularly unlucky, the replacements could have the same fault and cause the same symptom). If we don't do that, there will always be that doubt in our minds and we will keep coming back to that. |
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14th Dec 2018, 3:43 pm | #242 |
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Re: Cybernet PTBM121D4X problems
I think that L15 is just a little RF choke in that line and the set would probably still work without it - in other words, linked out, but don't quote me on that. I wouldn't worry about it, especially as it visually looks alright.
I thought that John hadn't tested the transistors that were actually in the radio yet, but had tested just the spare transistors from the scrap set - as in post #233, but I may have misunderstood what was described and missed the point. The easiest way to test the transistors in the set are to just suck the solder off the pads and carefully lift the three legs clear. Removing the transistors is best done by removing them complete with the heatsinks - as has been said. I did have a strange fault with a 1969 once where it tested fine on all junctions out of the radio, but wouldn't perform in the set. I removed, tested and re-fitted several time and replacing it with another restored normal operation. I did play around with this transistor, trying it again in the set and finally one of the junctions did actually read open, then I tested it again and it read normal. It must have been on the brink with a fault that only occurred when it was hit with RF, so strange things can happen, but it is very unusual and not very likely in the case of the radio under repair in this thread, although worth a thought. |
14th Dec 2018, 4:18 pm | #243 | |
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Re: Cybernet PTBM121D4X problems
Quote:
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14th Dec 2018, 11:31 pm | #244 |
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Re: Cybernet PTBM121D4X problems
Have removed 1969 and it took a bit of doing, replaced or not its been there
a long time results as follows base to emitter red/black 632 emitter to base red/black 1. collector to base red/black 1. base to collector red/black 625 collector to emitter red/black 1. emitter to collector red/black 594 will move onto 2166 now |
15th Dec 2018, 12:03 am | #245 |
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Re: Cybernet PTBM121D4X problems
And now 2166
Base to emitter red/black 644 emitter to base red/black 1. collector to base red/black 1. collector to base black/red 637 collector to emitter red/black 1. emitter to collector red/black 612 have tidied up the pads for what will go in |
15th Dec 2018, 1:44 am | #246 |
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Re: Cybernet PTBM121D4X problems
Have now fitted scrappers final and driver
after adjustment we have 10w fm,3w am and at a push 5w usb did notice one thing when i checked the transistors on for example the scrappers 1969 the 600+ reading is almost the same over the 3 readings on the 1969 out of this radio they differ, is that a sign of a "getting" faulty item ? so now fm is upto spec, need to find out why am and ssb are not, they are almost half power. |
15th Dec 2018, 11:39 am | #247 |
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Re: Cybernet PTBM121D4X problems
It's still not quite there, remember this is a high power FM variant so FM should be about 12W, possibly slightly more. Try retuning L8-L12-L14 again. Once you have FM up to what it should be, adjust RV13 for about 7W AM, but no higher. The SSB output appears to be a separate issue (drive? ALC?) But we can't sort that until you have the correct output in FM mode.
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15th Dec 2018, 1:43 pm | #248 |
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Re: Cybernet PTBM121D4X problems
Well this is interesting, hardly understand it my self
tuned radio on fm 20 mid could only get it to 10w flat out actually on each band, went to rv13, i turned it flat out and backed off a little am was then 6w on lo band 6w on mid band and 4.5w on hi band and thats flat out. am has backwards swing bye the way. i couldent understand ssb as its full voltage like fm so i went to rv4, then ssb output went upto 12w there was a little more but i left it at around 12w. this is the interesting bit, at that point i went back to fm it was now 15 or 16w, so i had to turn it down with l8 l12 etc to 10w spec the other two modes went down aswell so at the minute fm is 10w ssb about 10w and am is around a watt lower than before. looking like am output is the issue now,looks like rv4 has a lot to play in this game. i found somthing about set up of concorde 2, i know could be a little different, i think it was on the cb tricks site, will have another look for it, its more detailed from what i remember than the cybernet manual and spacifcally delt with the 121 chassis. thinking back i probably should have backed off rv4 instead of l8/l12. |
15th Dec 2018, 2:05 pm | #249 |
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Re: Cybernet PTBM121D4X problems
Looks like the ALC has more impact on FM / AM mode than expected, unless there is a fault in that area still. Anyway, the transmitter is starting to seem good.
I would expect that Peak SSB should be 12W, Constant FM should be 12W and AM with RV13 adjusted properly should be no more than 7W, because the AM Darlington's emitter voltage has to be able to rise and fall by a roughly equal amount in order to vary the supply to the finals +/- by about the same amount. |
15th Dec 2018, 2:18 pm | #250 |
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Re: Cybernet PTBM121D4X problems
Yes although 6w am max, makes you wonder if there is another adjustment
on am we havent come across yet or again as this is a fairly rough set up, it could be down to a better set up, rv4 is around 2pm looking from the back of radio |
15th Dec 2018, 2:35 pm | #251 |
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Re: Cybernet PTBM121D4X problems
ahh found it, it was on this pc it says on am
3.9 AM RF adjustment 1. set mode to AM 2. select band selector to mid 3. select channel selector to 60 (that would be 20 hi band ?) 4. adjust rv-14 for 4w rf power output rv14 havent done anything with that one before all this is on pdf like over 3mb per file 2 files, is there anywhere i can put on site for all to view. |
15th Dec 2018, 4:23 pm | #252 |
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Re: Cybernet PTBM121D4X problems
That 4W AM level sounds right for a USA market version where the levels had to be 4W AM and 12W SSB as per their regulations but the 'export' versions normally run at ~ 6-7W on AM and FM on variants where both modes have the finals running on the Darlington emitter voltage. On high power FM variants the FM constant output power should be the same as the SSB peak power.
If your file is too big to upload I can only suggest putting it on a service like "Dropbox". I don't have good access to a diagram just now so can't remember what RV14 does. |
15th Dec 2018, 4:43 pm | #253 |
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Re: Cybernet PTBM121D4X problems
RV14 AM C
I appreciate that they are different, but so far its all i could find |
15th Dec 2018, 5:09 pm | #254 |
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Re: Cybernet PTBM121D4X problems
Had an experiment with rv 14, it seems to do nothing in regards
to am power output apart from the size of backwards swing. so put it back to where it was. am is currently steady 4w on all bands |
16th Dec 2018, 1:05 pm | #255 |
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Re: Cybernet PTBM121D4X problems
"AM C" is a misprint or typo, it should probably read 'AM ALC' or 'AF ALC'.
A proportion of the output of the modulated supply voltage from the darlington emitter is taken through RV14 and turned into a negative DC voltage by D39 / C178. This in turn goes to Q35 (AF ALC transistor) which acts like a voltage controlled variable attenuator on the incoming microphone audio. In AM mode this serves to limit the maximum modulation otherwise the AM signal would be clipped at the top and bottom edges, causing distortion. If set too tightly, the AM output will be under modulated. You are supposed to set this adjustment by feeding an audio sinewave at a particular level, equivalent to loud speech, into the microphone input and observing the shape of the modulated output on a scope. Not enough ALC, the top and bottom peaks of the output waveform get flattened, causing distortion on AM TX. Too much ALC, the AM modulation lacks depth and sounds quieter than necessary. Slight under modulation is better than any amount of over modulation. The ideal modulation depth is probably about 90%. Step (7) on this page of the online 'Export' manual http://www.zen96216.zen.co.uk/cb/cybernet-esm-11.htm illustrates the ideal shape for a correctly modulated AM signal, but ignore the reference to RV12 in that paragraph as the procedure is referring to the PCMA001S chassis, not the 121. Last edited by SiriusHardware; 16th Dec 2018 at 1:17 pm. |
16th Dec 2018, 8:49 pm | #256 |
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Re: Cybernet PTBM121D4X problems
AM modulation sounds fairly strong with no distortion on ic 706
so ok for the time being funny thing is when you try to level off power output which would go to microbe adjustments its like smokin' mirrors. so anyway as a starting point i have fm just on or a smidge over 11w on each band. AM is 4 to just over 4 on each band and ssb is around 7w max and then we throw rv4 into the mix bit more complecated than i imagined, i would have thought as fm and ssb are both 13.6 or whatever their output would rise simultaniously, but dosent seem to be,as before when i had ssb at around 12w fm was 15 or 16w, havent been able to do that with ssb since. i now know the meaning of the word alignment, its like aligning the planets, lots of different permutations only one is correct |
17th Dec 2018, 1:27 am | #257 |
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Re: Cybernet PTBM121D4X problems
Did you set up that transmitter bias current yet?
I wouldn't worry too much about the discrepancy between maximum FM power and maximum SSB power. I'm assuming your power meter just has a 'power' range in which case it will probably indicate average power, rather than peak power. On FM, the power output is 100% flat out maximum all the time, the size of the signal does not vary (the frequency varies). On SSB the size of the RF output signal is proportional to the size of the audio input signal and only hits maximum for short periods of time on speech peaks, so the average power output is lower than the peak power out. Even with a sustained sound like a whistle into the microphone it can be hard to maintain 100% power output for any length of time. If your power meter happens to have a 'peak' hold feature try engaging that and see if the SSB power out seems closer to the FM power out. Whenever you do any tuning / balancing of the transmitter coil lineup, back the RF ALC (RV4) completely off so that the only factor limiting the size of the RF output is the tuning. Once you have the tuning lined up for maximum output balanced as well as you can across the bands, then bring the RF ALC back in to reduce the output on FM back down to whatever you consider it should be. RV12 is the audio drive level to the input of the SSB modulator, that will also affect the maximum output power on SSB. Set too low, SSB output power will not reach maximum output, set too high, the SSB signal will be driven into distortion. |
17th Dec 2018, 1:45 am | #258 |
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Re: Cybernet PTBM121D4X problems
I knew i had forgotten something...bias
age related issue nuumber xx !! yes the meter has peak hold it an avair av-600 should i do the bias part first or afterwards |
17th Dec 2018, 2:18 am | #259 |
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Re: Cybernet PTBM121D4X problems
Bias needs to be set first. Aim for ~35mA emitter current, SSB TX but -no SSB modulation- If you make any loud noises while doing this you risk blowing your meter amps fuse again.
Does this set have CW mode? |
17th Dec 2018, 2:54 am | #260 |
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Re: Cybernet PTBM121D4X problems
Can only do this on 20ma scale the reading will start at say on the meter 4.10
and climb up decreasing slowly adjust rv 2 microbe then it will start at say 2.10 and climb up getting 35ma is quite impossible as i dont have the gear to set hands free have to solder wire on emitter leg then connect to clip and use the ground probe to connect to pad se what it reads...eventually then if wrong switch radio off and make tiny adjustment and repeat the meter wont read it in a higher scale the radio dosent have cw |