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Old 29th Nov 2018, 11:49 pm   #121
John M1JWR
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Default Re: Cybernet PTBM121D4X problems

bit of a fiddley job that one
tests in order
r123 to rv7 1.
d48 to r117 00.6
c139 to pin 21 00.6
had to make up a lead with 2 crocodile clips for the job
here is a pic of solder side best i could get at the mo
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Old 30th Nov 2018, 12:27 am   #122
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Default Re: Cybernet PTBM121D4X problems

OK, referring again to that fragment of the layout I posted, the second dark grey track crossed by the line of the crack (top side) is also broken.

You can fix that one by soldering an insulated link wire similar to the last one to the points I asked you to measure between, but on the underside of the PCB. One end to RV7 wiper, the other end to R123, the end with the through-hole right beside it.

If you don't feel confident about identifying those points on the underside of the PCB, give me an overhead shot of the green side maybe three or four times as wide (so from further away) but still with the PCB fixing screw at top centre, and I'll mark the points where you can put a link wire to fix that problem.

Either way, restoration of this particular broken connection should get the AM/FM RX S-Meter working again.

Ultimately, it will be better to fix these breaks with short fine wire links soldered on either side of the breaks on the top side, but for now we'll keep using these diagnostic patch links, where necessary, to run the problems down one by one.
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Old 30th Nov 2018, 12:39 am   #123
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Default Re: Cybernet PTBM121D4X problems

Hope this ones ok
in my case when final repair comes will be easiest taking back panel off
that will make access simple i have plenty of old wiring from scrap radio etc
so some middle bits from some of that should do as its solid not stranded
and no doubt scrape a little of the track either side of crack's to make contact.
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Old 30th Nov 2018, 1:03 am   #124
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Default Re: Cybernet PTBM121D4X problems

Attached, your picture with the two points you need to link marked.

Remove the back plate to get easier access to that area, why didn't I think of that?? Good idea actually! But let's try to find the faults first.
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Old 30th Nov 2018, 2:41 am   #125
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Default Re: Cybernet PTBM121D4X problems

temp connection made, s meter now working
using genuine cybernet wire !!
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Old 30th Nov 2018, 10:27 am   #126
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Default Re: Cybernet PTBM121D4X problems

OK, next up, SSB RX?

On this radio, power on, USB RX, squelch off, clarifier centred. I assume this radio does not have +/- 5Kc shift.

On the sending radio (777?) transmit into a dummy load, -AM- mode but no modulation, on the same channel but at +1Khz, or one clockwise step to the right on the +/- 5kc shift. This will generate a steady signal for the USB receiver to receive, much easier than trying to whistle for 200 seconds or until you pass out, whichever happens first.

-Do you see an indicated SSB RX signal, but get no audio?
-Do you hear received audio (a 1Khz tone), but get no meter indication?
-Neither of these things?
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Old 30th Nov 2018, 11:30 pm   #127
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Default Re: Cybernet PTBM121D4X problems

Nothing seen or heard on usb with dummy load on 777 test
however when i added antron to 777 and dipole to this radio, an s5 signal on this
radio with a good strong tone 3 kc's clockwise.
on lsb also a s5 signal with tone, to get that 777 is 3kc's anti clockwise.
on am to am there is an s8 signal on meter and fm to fm an s7 signal.
on usb you will hear a dull tone starting at 1kc clockwise and on lsb dull tone
starting at 1 kc anti clockwise.
the clarifier is working, i think a little off centre, no sure as front is not on radio,
as its in good nick.
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Old 1st Dec 2018, 3:38 am   #128
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Default Re: Cybernet PTBM121D4X problems

If fully working and correctly tuned the receiver should get a full scale signal from a nearby transmitter, even one running into a dummy load.

You can get a relative comparison of sensitivity by putting the 10m radio on and transmitting to it from your 706 on about 10W into a dummy load. That will give you an idea of how the Colt should perform if you transmit to it from the 706.

It sounds quite deaf. With the front panel off, are you certain it is in DX, not LOC mode? You mentioned you had some sort of RF signal generator on the way, do you have more details about that?
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Old 1st Dec 2018, 1:13 pm   #129
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Default Re: Cybernet PTBM121D4X problems

yes very deaf, maybe years ago when problem started a screwdriver expert
got in and had a twiddle although there is no real sign of that.
i can test with the 10m radio & 706 i would think the signals will be MUCH larger,
yes i have now got a rf sig gen its one of those digimess 100 ones, i would have
to make up a lead for it with pl plug on one end and bnc on the other, i do have a couple of bnc's from the time i used to have a transverter years ago, will have to look and see if i have any thinner co ax as the usual thinnest stuff i have is
mini 8.
i did a quick test with the digimess it works though found a bit coarse in
adjustment for frequency, suppose the best way is adjust frequency until you hear it on radio, i take it that its a more modern revamp of those earlier ones
with the big dial.
i do have an audio gen that i got 3 years ago to do the ssb output on 777, i never got round to using it, its one of those with the dial and has rapid on it
as the maker.
Radio is in dx mode as when you flick switch its ever deaf'er !!
on a side note dont know if the nb/anl works not that that is a big problem
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Old 1st Dec 2018, 2:34 pm   #130
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Default Re: Cybernet PTBM121D4X problems

706 tx through power meter then dummy load 10w 28.460mhz
10m 320fm rx no ant
fm no s meter signal though can hear change in noise when 706 mic keyed
am s meter goes to s1 and change in noise when 706 mic keyed
usb s meter no signal can just hear modulation
lsb as above
antron connected to 706 through power meter, di pole to 10m 320fm
fm s8 r5
am s8 r5
usb s8/9 with feed back mod good
lsb as above
10m is a black hole for the di pole, thats why i have an antron 99
the tristar 777 is 12w on am carrier 8w on fm and 4w on ssb
so re did test with 777 to antron and cb colt to di pole
fm s7 mod quite low
am s8 mod very loud
usb s5 with lots of feedback modulation ok 1kc off
lsb as above
maybe not as bad as we thought, hopefully nothing a set up cant cure.
ive done some things in the past like the frequency counter for band
crystals and usb lsb off sets and that kind of thing.
i know power wise this radio is better lower down, i think there are two
adjustments for that
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Old 2nd Dec 2018, 1:40 am   #131
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Default Re: Cybernet PTBM121D4X problems

Sorry, should have said the Colt and 10m radio would both need an aerial for the tests.

It does sound like the radio may just need alignment but there is a transistor near the front end which effectively 'mutes' the receiver when the set is in TX - just need to be sure that transistor is operating normally and not de-sensing the receiver permanently, before touching any receiver adjustments. Away from base just now, will have a look at the diagram when I get back and suggest a measurement or two to rule that out.

From what you say re: Adjustments you've made in the past it sounds as though you will be able to do a fair job of tuning it back up, within the limitations of the test gear you have available. I haven't looked up the sig gen but as long as it is able to generate a very weak signal, equivalent to a real radio signal being received from miles away, it should be helpful when you are trying to do final alignment.
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Old 2nd Dec 2018, 2:05 am   #132
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Default Re: Cybernet PTBM121D4X problems

Just had a quick look at an online diagram -

In RX mode, check the voltage on the base of Q21 - asked you to do that once before but that was when the receiver was still half dead. It should be 0V in RX mode. If OK, power off, desolder the collector of Q21 from its pad and measure the resistance of Q21 c-e. Should be high resistance / infinite. Also desolder one end of both D19 and D20 and check them with the diode test feature of your meter. While you have these components disconnected do NOT go into TX mode on this set and do not transmit a strong signal in close proximity to this set until you have resoldered D19, D20 and Q21.
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Old 2nd Dec 2018, 6:23 pm   #133
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Default Re: Cybernet PTBM121D4X problems

Base of q21 0v rx
c to e of q21 is 1. with collector de soldered
d19 and d20 de soldered 2 pins parallel
so realised readings would be opposite way round between each one
anyway they say 631 one way and 1. the other with that in mind
all back together now
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Old 2nd Dec 2018, 7:07 pm   #134
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Default Re: Cybernet PTBM121D4X problems

OK, all sounds OK in that regard.

Take clear photo of T9, T10 and T11 so you have a record of the exact original angle at which the adjustment slots were set.

Try a signal from your generator going into radio on channel 20 on the middle band, AM receive mode, turn up the output level from the generator until the S-meter reads about S5, no more, and then carefully adjust T9, T10, T11 in very small movements either side of their current setting. If the meter reading decreases as you adjust to either side of its current setting and gives the best reading where it was, put it back exactly as it was, as it is already correctly set.

If the reading goes up as you adjust the coil in one direction and down as you adjust it in the other direction, then the coil is obviously already out of adjustment and you have nothing to lose by attempting to tune it up yourself.

While you are tuning for maximum indicated signal, the S-meter reading will increase, eventually to full scale. At that point reduce the generator output to bring the S-Meter back down to S5 and then carry on tuning. Every time the meter reading starts to get close to full scale, reduce the generator output to bring the meter back down to half-scale again so that there is always some headroom for improvement in the reading as you tune.
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Old 2nd Dec 2018, 7:29 pm   #135
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Default Re: Cybernet PTBM121D4X problems

had a test with that sig gen yeasterday, the frequency adjutment is very coarse
what i found is get it as near as possible, there are two other knobs on the front
coarse and fine amplitude adjustment, the fine one likes to be all way anti clockwise,
the coarse one strangely can also adjust the frequency, ive seen it do it.
the internal/external modulation can make a tone come through on radio even
though it says its for audio gen work only.when off carrier only.
can get a s5 signal on radio even more, s5 is required so will go for that.
so in otherwords will do the job but not what it says on the tin !!
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Old 2nd Dec 2018, 7:53 pm   #136
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Default Re: Cybernet PTBM121D4X problems

If the generator has more than one output - sometimes they have a 50R output and another output with some other impedance - hang one of your frequency meters off the other output so you can see exactly what frequency the generator is really outputting and keep adjusting back on frequency if necessary.

A rougher solution would be to use a BNC T-Piece in the output lead to fork off a portion of the output to one of your frequency meters.
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Old 3rd Dec 2018, 12:02 am   #137
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Default Re: Cybernet PTBM121D4X problems

The sig gen has 2 outputs 1 for rf and the other is audio input/output.
bnc t piece would be the only way to go, i dont have one of those.
anyway rightly or wrongly, i got the sig gen very close as signal appeared on
the radio and peaked it as i know the radio is pretty much on frequency and
worked from there, quite a bit of adjustment was needed, possibly somebody has been there before, eventually i managed to increase rx quite a lot and now
it is not far off the other radio with whatever config antenna/dummy load wise.
of course this radio is still much more sensitive on low band than hi band
though i realise there will be other adjustments for that.
i know a guy back in the day he would use another radio that he knew was good
and put an elastic band round the mic as a make shift sig gen.
elastic band round the mic, that takes me back, music players and mic keyers
did that back in the day.
anybody guilty !!??
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Old 3rd Dec 2018, 1:31 am   #138
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Default Re: Cybernet PTBM121D4X problems

It was the only form of signal generator most people had, so forgivable in many ways. The problem with it is that it is almost impossible to generate a weak enough signal to do the final tuning using that method, as any signal at all in the local area gives FSD on the meter. That's why a signal generator is really the only way to go if you are doing the job properly.

For the high end / low end balance problem the usual method to start with was to peak on the middle channel of the middle band and then check reception on the highest channel of the highest band and lowest channel on the lowest band to see which was the more sensitive, and then turn the front end coils (T9 to T11) a fraction inwards if the radio was more sensitive on the highest channel and a fraction outwards if the radio was more sensitive on the lowest channel, constantly switching between the two until the sensitivity at each end was the same.

That first stage usually results in the radio being most sensitive in the middle of its coverage and slightly (but equally) less sensitive at the ends. Without serious test gear that is probably enough of a compromise for most people.

If you want to go the whole hog you can then try readjusting two of the front end coils slightly off centre, one peaking on (say) channel 10 of the upper band and one peaking on channel 30 of the lower band. The effect of this, if you get it right, is that the sensitivity is raised a little at both ends and flattened a little in the middle and so is more even across the whole coverage of the set. For that sort of fine tuning you really need a signal generator which produces a rock steady constant RF output level all the way across the radio's coverage.

I agree with your general premise - originally the radio failed because of that crack and someone tried, as they always do, to 'fix' it by twiddling with adjustments which had been perfectly set before the set failed due to a physical fault, thereby compounding the problem. That is the reason I gave up working on them for other people decades ago, because I got so fed up with fixing either self-inflicted faults or with fixing simple faults and then also having to patiently re-align the set as well.

Last edited by SiriusHardware; 3rd Dec 2018 at 1:40 am.
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Old 3rd Dec 2018, 2:11 am   #139
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Default Re: Cybernet PTBM121D4X problems

yes i will have a good shot at "levelling" it out and hopefully that will be that in the rx stakes so tomorrow nights job!
only 2 issues left and a tricky soldering job at the end
low output power less than quarter of a watt all mode
and squelch muting ssb on signals less than at a guess s5
had a quick sneck at rv11 on that one diddent seem to do anything so
returned to original position
squelch works perfect on am and fm
will be back when ive done this job, many thanks
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Old 3rd Dec 2018, 2:33 pm   #140
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Default Re: Cybernet PTBM121D4X problems

Just had a look around for information about your Tek 2225 scope. Whether by accident or design it happens to be a 50Mhz scope, a bit higher end than most old scopes. It's perfect for looking at the RF out waveform as it passes through the transmitter, so we'll use that when we get to the transmitter problems.

Manual is here, in case you don't already have it.

https://www.tek.com/node/830993-manual/2225
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