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Old 14th Nov 2018, 12:18 am   #21
John M1JWR
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Default Re: Cybernet PTBM121D4X problems

There is no pin 42, just a through hole, there is a pin 44 next to it
got an idea tho
if i put the end of a multimeter probe in through hole and put a piece of wire in the other end and touched it to a can
might that work

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Old 14th Nov 2018, 12:49 am   #22
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Default Re: Cybernet PTBM121D4X problems

Sorry, that's what I get for using the wrong diagram (I still have not found my specific Colt 320 diagram, so I was using the one for the Concorde II).

Try it another way, same setup as before but unplug the earth-side (Green?) wire from the speaker and connect that side of the speaker to 0V with a croc-lead or similar. What happens then?

Does the 320 have any of the following:

-An off board roger beep?
-An off board relay on a small PCB, mounted to the metalwork with a metal bracket?
-A 6-pin Molex 'selcall' connector mounted on the chassis rear?
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Old 14th Nov 2018, 12:55 am   #23
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Default Re: Cybernet PTBM121D4X problems

very much the same as tristar 747
they were known as the fixed models no beep's, kc shifts no relay's or sellcall
schematic for 747 may be more accessable
connected one end of multimeter probe rig to speaker and other to a can
the result is no sound
however with removing the yellow wire i get the same low volume level as with wire connected to speaker

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Old 14th Nov 2018, 1:32 am   #24
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Default Re: Cybernet PTBM121D4X problems

OK, obviously the yellow wire, not the green wire, must be the speaker earth side wire in that set.

If you have not already done so, try plugging an extension speaker into the EXT SPK socket (not the PA socket) on the rear of the radio. This is to check the cut-off switch inside the EXT SPK socket along with the wiring going to it, not the internal speaker which we already know is probably OK.

Check resistance of R169, large 4R7 resistor between / near wire terminals (37) and (38).

Same setup as before (Receive, FM mode, squelch fully down) can you 'scope' the following points, if they exist.

-Wire terminal (21). Any audio seen here will be at a fixed level independent of the volume control. You are looking for no-signal white noise from the AN240P at this point.

-Wire terminal (25). Any audio here will be variable according to the setting of the volume control.

-Wire terminal (28). Any audio here will be very large, and will vary according to the setting of the volume control.
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Old 14th Nov 2018, 2:04 am   #25
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Default Re: Cybernet PTBM121D4X problems

Hi
will have a look at the scope part tomorrow night
dont have extension speaker had to use headphones in ext jack
same low audio comes through phones
when phones are connected nothing comes through internal speaker
have checked resistor that is still connected to mainboard
i get the following
radio off 0.68 ohms
radio on same
meter is on where it says ohm power and to 200 scale
it is a uni-t ut58a

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Old 14th Nov 2018, 12:34 pm   #26
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Default Re: Cybernet PTBM121D4X problems

New rule: Only ever make resistance measurements with the power to the unit off - not just on this radio, but whenever you are trying to make a resistance measurement on anything. The meter readings will be upset by the voltages present in a powered circuit.

The reading you have for the resistor sounds strange, to be sure perhaps the best thing to to is to desolder one end and measure only the resistor. While it is disconnected, also measure the resistance between terminals (37) and (38) again.

Let me know how the scope tests on the aforementioned wire terminal test points go.
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Old 15th Nov 2018, 12:14 am   #27
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Default Re: Cybernet PTBM121D4X problems

Hi
firstly r169 on scrap board same scale on meter, as resistor is still in situe
its reading is 05.3, then i rechecked resistor in this radio and it is 05.4
radio off and disconnected from psu, i reckoned you would say de solder it,
so i thought i would try it this way first as a comparison.
from what i remember i dont think scrap radio had a problem with rx audio.
anyway scope test, as i am no expert i adjusted scope down or is it up
for a reading on pin 21, x1 mag volts/div to say 5m in 1x box cal turned all the way to right before the switch bit whatever that is for,
the signal is level with 1st half markers above and below centre line,does not change with vol operation.
Pin 25
min vol half way to the half markers, at full vol its half way between half markers
and first full lines across screen,
Pin 28 hard one to get at,its near power socket, lots of wriggling lines going up and down, turn volume up and there is some variation higher and lower but not a lot.
on the other two pins it looks like a thick line no wiggly lines
had to earth scope on ground pin in radio as its too small for cans.
hope you understand all that because i dont and i just wrote it !!
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Old 15th Nov 2018, 2:02 am   #28
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Default Re: Cybernet PTBM121D4X problems

I've just put this through Google Translate, and broadly I think it says:

The resistor, when you measured it again, was close to the expected value and similar to the same resistor on another board.

Pin 21, you saw some white noise on the scope as expected.

Pin 25, you saw some white noise and were able to affect the level of it using the volume control, again, as expected.

Pin 28, you got very little (which is not what we would expect) but what there was was affected by the volume control setting.

Correct?

Using any actual ground pin such as the G or G1 wire terminals for the scope ground is fine, it's just that it is usually easier to find a coil can. The metal 'box' around the output transistors should also be a good 0V, as far as I remember.
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Old 15th Nov 2018, 2:38 am   #29
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Default Re: Cybernet PTBM121D4X problems

pretty much
pin 28 has quite a lot more action than the other two when the lines squiggle up and down sometimes reaching almost to the line across screen where it says 90
and 10 on the side at full volume
in otherwords i will call the centre line 50 and half lines 60 above and 40 below etc.
pin 21 at 60 and 40
pin 25 say 65 and 35 full volume
pin 28 peak sometimes 90 and 10 and different pattern, lots of moving squiggly lines.
the other two look like a very thick line across the screen
havent used that scope in years and even then only little
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Old 15th Nov 2018, 3:21 am   #30
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Default Re: Cybernet PTBM121D4X problems

From what you're saying, it sounds as though the signal on pin 28 is actually bigger than on pins 21 and 25, which is to be expected. It's a bit early in the morning for me to think straight, let me look at the diagram again tomorrow.

In the meantime, a word about scopes.

The Volts/Div switch has 'voltage per division' markings next to each click position, and a line marked on the knob which points to the current setting.

Let's say that you have that knob set to 1V/Div. What that means is that each vertical square going up or down from where you have the trace centred represents one volt.

If you have the trace centred on the centre line of the scale and you then scope a signal which extends up to two squares above the centre line and two squares below the centre line (so it is four squares high altogether), then the signal is four volts peak to peak.

If you had the Volts/Div switch set to 0.5V/Div and a signal on the screen which was four squares high, each vertical square would now equal 0.5V so the size of the signal in this case would be 2V peak-peak.

The Volts per division (and Time per division) markings on the knobs are only accurate if the variable fine-tune controls are set to their 'Cal' position and left in that position.

The Time/Div knob, not surprisingly, sets the amount of time that each square across the screen represents, so if you have it set to '1ms' it takes the trace 1ms to traverse the width of one square on the screen. For a rough ballpark setting for looking at audio, first wind the Time/Div switch all the way down to the slowest speed and then rotate it clockwise to the point where the trace is just travelling fast enough to seem like a solid line.
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Old 15th Nov 2018, 11:41 pm   #31
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Default Re: Cybernet PTBM121D4X problems

noted about scopes
the only thing between output of af amp and pin 28 is c173.
anyway to me as a laymen it looked like a lot of noise on pin 28.
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Old 16th Nov 2018, 1:00 am   #32
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Default Re: Cybernet PTBM121D4X problems

It -is- noise: .

You know the sound you normally hear when you're on FM, there is no signal and you turn the squelch down? - that noise. You're hearing it faintly when the squelch is off, but it should be deafening with the volume turned up more than about 30%.

You don't know if the receiver is functional yet, so for the time being we're using the AN240 FM discriminator IC as a handy source of sound to follow from the end of the receiver, through the audio power amplifier and out, eventually, to the speaker.

What's useful about that is that it is the AN240 itself which makes that noise when it doesn't have a signal to lock on to and it will do that even when the rest of the receiver is non-functional, so it's a handy built-in source of test audio for this purpose.

-FM receive
-Squelch right down
-Volume at 50% (12 o'clock)

Take your scope back to pin 25 and this time, while observing the signal there (which should look like a thick band of random noise, as I think you said it did) - twist the volts/div knob until the signal, from top edge to bottom edge, is filling roughly half of the scope screen, say two or three squares up and down from the centre line. Try to remember what it looks like, or even take a photo on your phone.

Now move the scope probe back to pin 28 and turn the volts/div control anticlockwise until the signal there is occupying roughly the same height on the screen as the signal on pin 25 did. Does it now look similar to the signal you had on pin 25?

Pin 25 is before the audio power amp, Pin 28 is after the audio power amp. If the audio power amp is working, which I think it is, because the radio works in PA mode, then the signal on pin 28 should be the same as the signal on pin 25, only much, much bigger. Because it's so much bigger, you have to turn the volts/division down quite a bit in order to get it to look the same there as it does on pin 25.

If you can establish whether you do (or do not) have a big noise signal present on pin 28, we'll take it from there.

Can you try another speaker? - sometimes speaker coils get stuck so they can barely move and hardly produce any sound. The fact that you have almost no audio through the EXT SP socket either makes this unlikely to be your fault but it is an easy thing to try.

Can you also try some other Cybernet wired microphone, as the speaker audio earth return passes through the microphone on some models with this chassis (on some others, it passes through the little relay, which your set does not have, instead).
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Old 16th Nov 2018, 1:09 am   #33
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Default Re: Cybernet PTBM121D4X problems

ok will crack on with that after work tomorrow
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Old 17th Nov 2018, 12:58 am   #34
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Default Re: Cybernet PTBM121D4X problems

Hi
lets see if i can upload 2 pics
any adjustment other than these settings make the signal smaller
1st pic small signal 5m volts per div and .01 ms per div pin 25 vol a around half volume
i can make i bit bigger when i turn volume to full, but not a lot
2nd pic
pin 28 5m volts per div 2 ms per div, as you can see much larger
please ignore shadow across pic 2, its from lamp
the scope was my dads he's been dead over 20 years, he showed me bits about it, that now
i cant really remember
these were taken in pp auto mode whatever that is as normal dosent seem to work
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Old 17th Nov 2018, 10:31 am   #35
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Default Re: Cybernet PTBM121D4X problems

If you used the same volts/div setting (5mv/div) for both pics then it shows that the signal is being amplified between the first point and the second but both are a lot smaller than I would expect. With the volume up at half way I would expect to be seeing Volts at pin 28, not millivolts.

The scope probe, if you are using one, does it have a X10 / X1 slide switch on it? Which position was it in when you made those measurements?

I'm away from base as I usually am at weekends - when I get back I will try to see if I can find out what those levels should typically be.

Did you try another microphone? If you don't have one just try shorting the two pins furthest away from the 'bump' on the four pin microphone socket, those are the two pins which would be joined together by a working microphone in RX mode.
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Old 17th Nov 2018, 12:35 pm   #36
John M1JWR
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Default Re: Cybernet PTBM121D4X problems

Hi
Scope probe was on x1
did try another speaker that was on scrap radio, same low volume
and shorted the two pins, also same result
i have a pic of block diagram here, going backwards so far
sp out
af power q34/ic5
q19 product detector, have checked that one in the past and voltages on it were correct, then q14/16/17
fm detector ic6 and am detector d25
am if q27/28/29
then crystal filter etc
loads of components in the audio amp area for starters
eek !
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Old 17th Nov 2018, 5:35 pm   #37
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Default Re: Cybernet PTBM121D4X problems

I think the audio amp itself is ruled out because you said it worked when you tested it in PA mode (presumably with phones plugged into the PA socket).

It's a shame you don't have an actual extension speaker, if you mean to do more of this sort of thing it wouldn't be a bad idea to get hold of one, they are a generically useful thing to have. For example, when you are trying to work on these sets it is a pain to have the lower 'lid' tied to the rest of the set by the speaker wires. If you have an extension speaker you can plug that into the rear socket, and unplug and remove the lower lid and speaker and set them aside.

You need to sort this audio level problem out first before trying to get anything else receiver wise working.

When I get back I'll see if I can dig out something from my 'museum' with a Cybernet chassis which is broadly similar in the same areas and measure up the noise levels at the equivalent points. Probably won't be able to do that until Monday evening, though.
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Old 17th Nov 2018, 5:54 pm   #38
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Default Re: Cybernet PTBM121D4X problems

You reckon a component gone somewhere
anyway cybernet musieum !!
You will be looking for something like a tristar 747 from what i remember they were the most common with 121 chassis.
maybe i can help a bit as i could test 777 even tho it has 125 board
its rx audio is working well, may give a clue.
i think its basically a similar idea with mostly the same parts
regards
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Old 17th Nov 2018, 7:46 pm   #39
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Default Re: Cybernet PTBM121D4X problems

My 'Museum' is not so large that I can pick from a variety of 121-chassis radios.

More likely it will be something with a 134 (UK FM) chassis but there are some good similarities (Same AN240 FM discriminator IC, same TA7205 audio PA) so I would expect that the signals would not be too dissimilar at the equivalent points when the 121 chassis is in FM receive mode.

Actually, I forgot you'd had said you had that 777. So, if you put power on the 777 do you get a nice loud roar from the speaker when it's in FM mode with the squelch turned down?

If so, try looking at the equivalent points on that chassis for the size of the signals there, compared to the ones you are getting on the 121 chassis. They would be wire terminal 17 (Input to audio amplifier) and wire terminal 9 (Output from amplifier). The two radios are not completely identical in this circuit area due to the 125 chassis using an AN7140 power amp instead of the tried and trusted TA7205, but I would expect the audio levels to be broadly the same on both chassis.
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Old 17th Nov 2018, 11:38 pm   #40
John M1JWR
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Default Re: Cybernet PTBM121D4X problems

Hi
I had forgotten that i had another radio, another colt 320 but hold you horses
this one's a bit different, its a 10m one done with a prom, thinking back i got
it via radcom off a G4 about 15 to 20 years ago, it even does a crude form of splits for the repeaters.
anayway it should be good for comparisons with this radio as its rx audio is fine
ive been through parts of it that i think may be relevent, the scope part was interesting
pin 25 was same wave pattern as before with scope at same settings however when volume is turned up the wave lines dance up and down but keep the same form, adjustment on scope just makes the waves smaller and they do the same thing.
pin 28 was interesting with volume on minimum and squelch on, the waves almost fill 1 sq up and down of centre line.
as soon as squelch is off the waves become distorted and bounce up and down all over the screen, as volume is increased the waves become more distorted and eventually dissapear off the screen
again the adjustment of volts div only make the waves smaller but the still do the same thing.
voltage checks, i havent done the avr and darlington on the 10m radio, but did a lot of other places so i have something to compair to
so where i finished with the 10m one i started with this radio.
squelch transistors q31 to 33
please note that i may have base and emitter wrong way round sometimes
10m radio fm mode squelch off then on
q31 off 2.8v/0.70v/2.1v on 1.28v/0v/1.91v
This radio
q31 off 2.27v/0.73v/1.64v on 1.31v/0v/1.48v
q32 and 33 are same as 10m radio
seems like q33 is quite a bit off
could this be our first clue !!
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