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Old 20th Nov 2018, 2:33 am   #61
John M1JWR
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Default Re: Cybernet PTBM121D4X problems

have fitted the 2 parts back in no link as yet
on 200ohm scale the reading is 00.8ohms
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Old 20th Nov 2018, 1:58 pm   #62
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Default Re: Cybernet PTBM121D4X problems

Between which points? Looking at the state of the connecting track (not too bad) I would say you probably have a good connection between Q32 Collector and Q33 base and C157 + and R131, one end, which you can prove by measuring from each of those points to each other point, it should be very low resistance any way you measure it.

If so, it's another thing ruled out, unfortunately.

It's a shame you aren't a little bit closer, we could probably pursue this more easily on two metres. Trying to fix it this way feels like playing chess by post.
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Old 20th Nov 2018, 11:22 pm   #63
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Default Re: Cybernet PTBM121D4X problems

Hi
Yes 2m would be very handy, though very good of you to stick with this.
anyway i did a comprehensive check of the area ans results as follows,
it may give some indication, radio no power.
all taken on the 200ohm scale
C of q32 to B of q33 03.6 falling did this one again a little later and was 02.4
and falling slowly,
C of q32 to + of c157 03.4 falling
C of q32 to + of r131 03.0 rising slowly
B of q33 to c of q33 08.8
C of q33 to E of q33 08.9
E of q33 to B of q33 08.9
Q33 to ground
B 08.9
C 09.0
E 01.2
R131 + to ground 08.9
C157 + to ground 08.8
C of q32 to ground 08.7
Forgot to say squelch knob was on a little maybe about 25%
regards

Last edited by John M1JWR; 20th Nov 2018 at 11:40 pm.
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Old 21st Nov 2018, 2:02 pm   #64
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Default Re: Cybernet PTBM121D4X problems

Sorry, was a little busy with a project last night.

The resistance readings around Q33, esp. Q33 b-c-e to 0V seem very low, can you either remove Q33 or desolder at least two legs of Q33 from their surrounding pads and check the resistance of Q33 c-e, b-e, c-b on the low ohms range?
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Old 21st Nov 2018, 11:59 pm   #65
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Default Re: Cybernet PTBM121D4X problems

Hi
done this check just now, have removed q33 all 3 pads look in good condition.
on 200 ohms setting C to E 09.6 C to B 09.3 and B to E is 09.6
also did the pads to ground both C and B are 1 (infinity) and emitter pad is 01.3.
for interest the transistor is marked ci740 must be a varient to c945
regards
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Old 22nd Nov 2018, 12:27 am   #66
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Default Re: Cybernet PTBM121D4X problems

As a postscript to this i have tested two c945's that were removed from scrap radio and with same spec connections the pins tested infinity
if thats the case i take it that the one in previous post is u/s
just the reading on emitter pad i am not sure about
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Old 22nd Nov 2018, 1:10 am   #67
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Default Re: Cybernet PTBM121D4X problems

Yes, the emitter of Q33 does go to 0V, so that is correct.

With your meter on the 200R max range, a healthy transistor will seem infinite / open circuit from every pin to every pin (If you select a higher range you will start to see resistances which will be different between the various pins, and will depend on the direction in which you are making the measurement).

Don't worry about that for now though, one thing you definitely should not see on a healthy out-of-circuit transistor is resistances in the order of ten ohms between any of the leads, so Q33 is definitely defunct. Go ahead and change it.
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Old 22nd Nov 2018, 2:07 am   #68
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Default Re: Cybernet PTBM121D4X problems

put in fresh c945 base and collector tested to ground show infinity
emitter shows 01.5
ready to switch on ?
if so fingers and anything else for that matter crossed !!
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Old 22nd Nov 2018, 11:22 am   #69
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Default Re: Cybernet PTBM121D4X problems

Yes, of course, have faith! If this goes as planned you should be back to the point where the squelch action is working again (speaker thud as you turn the squelch back and forth through the threshold).

You may still have very quiet unsquelched audio, which is the problem we were trying to track originally.

If so, we can get back onto that.
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Old 22nd Nov 2018, 11:42 am   #70
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Default Re: Cybernet PTBM121D4X problems

Yes can confirm its back to the way it was before possibly a tad louder !
did notice last night that on 1 pin of r132 the one that goes to i think c164
the track aint very good there right next to r132's pin, its making contact but only just. will put a link there in the future.
on to the present, got another job on this morning so will back on here after work, gives a little time to work out next plan of attack !!
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Old 22nd Nov 2018, 2:12 pm   #71
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Default Re: Cybernet PTBM121D4X problems

Two more diagnostic shortcuts you can try, both with power on, squelch right down, FM receive, microphone plugged in but PTT not pressed.

1) Temporarily connect a link wire (crocodile lead, etc) between wire terminal (21) (AM/FM receiver output ) and wire terminal (25) (Audio amplifier input). Do you get loud FM 'roar' if you do that?

2a) Connect a temporary speaker between C173 negative side and 0V. Do you get loud audio out of the speaker?

2b) Temporarily replace C173 with the same part from another chassis. Do you get loud audio from the unit's speaker?
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Old 23rd Nov 2018, 12:29 am   #72
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Default Re: Cybernet PTBM121D4X problems

First test made the volume when it was low go upto the low max that we have
the 2nd test made no difference
had higher hopes for the third test as when i removed c173 there looked a
small sign of leakage, i replaced cap with the one out of the scrapper which is a 25v varient again unfortunetly no change did make a note of neg side.
betcha its going to the last thing, and a why diddent i think of that in the first place kinda thing !!!
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Old 23rd Nov 2018, 12:55 am   #73
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Default Re: Cybernet PTBM121D4X problems

First test sounds right, as you were bypassing the volume control.

Can you confirm the radio still works in PA mode - ideally with a speaker connected to the PA socket. An old stereo speaker, car radio speaker, anything like that which you can put a 3.5mm mono jack plug onto. As I'm sure you are aware the volume control controls the output volume in PA mode, so give it plenty of welly and make sure the PA audio is good and loud in the way that the receiver audio just isn't. If you have plenty of volume from the PA output that should definitely rule out the Audio PA IC itself.

Do you have any transmitter output power in any mode?
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Old 23rd Nov 2018, 1:56 am   #74
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Default Re: Cybernet PTBM121D4X problems

only i could test was with whats connected to pc took it off pc 3.5 jack and plugged it in cb the other end goes through a kenwood hi fi amp and out of a pair of mission 762i's, the hi fi amp 30% vol with that anything given by cb through pa with any more than a slight turn on cb's volume is deafining.
in any case when you turn cb on there is a loud sort of crack and when mode is changed with the kinda dirty mode switch its loud, all much louder than the rx audio.
The radio has tx output on all modes though very low, less than quarter of a watt, i tested that with my avair swr/power meter 5w scale
i have also tested radio with dummy load connected and icom 706 rx on 26.515
its connected to 80m di pole, modulation comes through on icom well at signals from s9 to +40 depending on mode.
hope that helps
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Old 23rd Nov 2018, 10:13 am   #75
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Default Re: Cybernet PTBM121D4X problems

So you're getting modulation on all TX modes?
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Old 23rd Nov 2018, 11:24 am   #76
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Default Re: Cybernet PTBM121D4X problems

Yes
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Old 23rd Nov 2018, 1:05 pm   #77
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Default Re: Cybernet PTBM121D4X problems

And I take it the volume of the audio on all modes is as loud as you expect it to be? Not quiet? I'm asking because all of the voice TX modes take their initial audio from the output of the Audio PA IC, so if the modulation levels sound normal, that, along with the PA test, is another indication that the audio PA is OK.

The evidence so far is suggesting that the audio output level from the AM/FM receiver output is much lower than it should be.

With power on, mode AM RX (not FM) volume fully up, squelch off, microphone plugged in but not keyed, hold an all-metal pointed object like a jeweller's screwdriver in your hand and touch it first to wire terminal (25) and then to either leg of C160, which is next to Q34 which is associated with the audio PA IC. Do you hear a buzz/hum through the unit's speaker when you touch either of those circuit points?
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Old 23rd Nov 2018, 1:09 pm   #78
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Default Re: Cybernet PTBM121D4X problems

In FM RX mode, squelch off, what supply voltage do you see on pin 5 of the AN240P IC? What size is the noise signal coming out of pin 12 of the AN240P? (Measure on a scope).
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Old 23rd Nov 2018, 11:50 pm   #79
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Default Re: Cybernet PTBM121D4X problems

Have done two of these tests so far
first test i take it you meant, as i used a piece of wire, one end to pin 25 etc
and other end grounded to my hand, if thats the case both components gave
a loud hum/buzz.
2nd test, i did voltages on all pins on fm ic and are as follows
1 2.02v 2 2.02v 3 0v 4 0v 5 7.8v 6 0v 7 6.67v 8 6.05v 9 3.77v 10 3.77v
11 0v 12 3.58v 13 4.28v 14 1.58v
will take a bit of time to get the scope set up, report later
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Old 24th Nov 2018, 12:45 am   #80
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Default Re: Cybernet PTBM121D4X problems

Dont know if scope test tells you anything
1v per div.5 sec per div, centre line only
scope wont measure it below that ie 50m 20m etc centre line goes off
the screen and you cant get it to come back
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