Galaxy Saturn base radio - no transmitted audio.

[26TW06]

Hi,
apologies that its been a while.

I did a little more checking today under your instruction:

"Now, I need you to check D71's BANDED end - what is your voltage in TX then to RX?"
7.7v in RX
4.6v in TX

"Then go to PA mode, and do this again D71 TX and RX..."
7.8v in RX
7.8 in TX
D71 is good, and not shorted. was removed from the circuit to test

"I need to know the Voltages on TR38 - PNP and TR37 NPN. In RX and TX."
TR38 is a 1282 which apparently the emitter and base are reversed
8.49v on the Emitter RX
0v on the collector RX
7.97v on the base RX

8.43v on the Emitter in TX
8.34 on the collector in TX
7.66 on the Base in TX

T37
7.9mv on emittor in RX
0.9v on the collector in RX
0.65v on the its base in RX

000.3mv emittor in TX
7.9v collecter
000.3mv base

TR40
1v on the emitter in RX
12.9v on the collecter in RX
1.61v on the base in RX

0.98v on the emiter in tx
12.68v on the collecter in TX
1.60 drops to on the base in TX

TR36 is also a 1282 with the emitter and base reversed
8.5v on the emitter for RX
8.48 on the collector in RX
7.78v on the Base in RX

8.43 on the emitter ini TX
6.9mv on the collector in TX
7.93v on the Base in TX


I located D85 and clipped it as you instructed.

Checking TR34, I got the following readings:
RX E 7v
RX C 7v
RX B 6.2V

TX E 5.3v
TX C 0.5v
TX B 4.6v

I checked these again in AM mode on channel 40 band D as the manual suggests.

Cheers,

Darren

 

[Handy Andy]

Ok! Great job, working on those numbers for you...

Looks like TR36 is "turning off" so the RX side is going down. IF there were diodes that were band in the RX line - those kinds of issues, TR36's "output" - being the Collector - would still be high - for one of two reasons, the Collector Emitter is shot, or there is a Diode or wiring problem in the RX line, holding it high, and keeping TR32 still active - muting your radio.

The D85, is the "Crossover" diode from CW key to the USB LSB mode - so if you find "CW isn't working" it is due to D85 removed. D85, when in CW mode, powers the USB/LSB 10.695 oscillator and sends that to Pin 3 of the Balanced Modulator.

Wanted to know if Audio did return - how? By the AN612 using that 10.695 oscillator. You'd hear a "monitor" tone and TR32 would allow the "peep" to be heard - you don't hear it in AM - just the "Delay" - so you did check R179 and found it to be a high Meg-ohmic rated resistor

IF you cannot restore audio thru that, then reinstall D85 to restore CW, but you will also need to look at D84, which steers power from the Mode switch to that 10.695 oscillator. You can look for that at D85's Banded end when you reinstall it, you would see it active in CW and USB and LSB modes, but nothing else.

Here's the thing that kinda' rubs me, locate D84 and check it. to make sure that it sends power to that 10.695 section. Again, that can be verified at D85s' Banded end - if voltage appears, you're ok it means the diode is too.

Only other thing to check would be TR34...and D83 - works off of the 8 volt regulator and is a 2SA733, so its' BASE is applying power all the time - sends it thru D83 - into the two Audio Limiters - SSB ALC - TR47 and AMC Limiter DETECT TR53.

Which takes us back to D70, and D71 - which seems to be ok, - so Since TR34 POWERS AMC and ALC - it stands to reason that if you kept TR32 in place and pulled TR34 - you should have audio return. But the problem here is...

TX the Collector is going to 0.6 - still tells me it's making TR32 turn on enough - so we have to locate what or why TR34 is holding TR32 high. So I'm thinking that the Bias resistors R177 and R176 are doing this mess to you...

You may need to go over those ALC and AMC amps... I'm giving you what I'm working with so you know where I stand on this...

Made an error in Cap ids' earlier, C134 is the Roger Peep Delay cap - Goes to Silkscreen Pin 73 C133 is TX "cushion" cap for TX switching.

 

[Handy Andy]

I was doing some thinking last night over this...

We may need to try a different approach.

Unfortunately I have posted this before in other forums about an effect that some radios tend to oscillate and seem to act unstable - all due to a very high-frequency "squeal" that happens to amps when they have issues like bad capacitors that affect their gain in the stage of the strip. Making this one section inject an extra signal mixing in with the lower frequency-audio signal - they are simply two signals passing thru the stage.

I got flamed a long time ago by someone over the HR2510 - the Mic amp in that radio is a simple 4558 SIPP chip, and as many of you know, the 560pF cap can be removed to help "open" the audio - AS LONG as you keep the limiters intact and don't re-work the stage in an attempt to maximize the audio bandwidth or power levels - most operators won't experience this ultrasonic effect of two signals mixing together and the radio trying to sort them out.

Ok, your issue is that TR32 keeps "engaging" - so I looked thru your posts and my notes and one thing we haven't touched on yet, is keeping TR32 in there, but taking away the sources of bias - or trigger voltages - so you mentioned in an earlier post, you measured across a resistor - 2.2K ohms, I think that is where your problem begins.

Many parts are supposed to stay in tolerance but when you saw 2K2 - at first I think even I thought it would be ok, but I found out later, there used to be a different flavor of transistor in the EARLEIR boards.

The Bane of the 458 versus the 945 - (2SC series) this has come up before and it's how these two parts work in the same circuit - so with you going with the 945, the 458 older BIASING style may need to be changed.

I have some pics of an older 360011Z board and it's Mic amp values - it may help you...will post these today as time permits.

 

[26TW06]

Hey Andy,
Thanks again for taking the time to supply all this info.

Forgive me if I have misunderstood, so its possible that the original Tr32 in my radio may have been something other than the 945? Which could have been more tolerant to the higher voltage present?

It could be worth replacing resistor (R178 4k7), measuring only 2k2? The bands on it showed that it should be 4k7. Can't be a waste of time right, as its out of spec now.

Cheers,

Darren

 

[Handy Andy]

Well, hold on. been working on something for you, didn't know if you caught this...


I'm working on getting some pics from a board that is in the generation of yours, it just doesn't have the PA circuit - for in their revisions of all the boards Cybernet and Uniden did, they found ways to streamline their boards as a method of standardization. One of them being to have a separate PA amp to be a Bane - so they simply reworked their boards to remove the separate PA amp, and piped all audio thru Mic amp so they had just one audio line sourced and they can then apply switched routings to drive the PA thru more common circuits - Cobras 148 and Grant XL's have the similar "roots" of design.

I wanted you to note that, yes, you may have a bad resistor - but it may not be the one you think.

Look at the schematic, I've got the route TR32 uses for its' "trigger" highlited. I hope you can see that there are TWO feeds going into this part. One being the ALC and AMC amps - their DIFFERENCES are piped thru the BASE lead of TR34, affecting the output of TR34 in which feeds TR32.

But, the Audio from the MIC amp is also sent thru and ties into here. D69 being the DC Block to keep the ALC/AMC from interfering with Mic amp output

You have several choices, one - change R177 and R176 values which change how the ALC and AMC circuits function and their impact, or change R178 to affect both.R178 being the one with the "final say".

The older 945 and 458 debacle is ongoing - but the results are still the same, the values used for one part to bias, is different that what is needed to accomplish the same result - on another.

 

[Handy Andy]

Now for other efforts...

Look at that Mic amp side of the 4558...

​

It stands to reason that many of these resistors should be ok, and within tolerance, but remember too, the 4558 is an Op Amp - meaning it can operate as a switch - so if the resistor biasing isn't right, the op amp works and operates on the inputs as if it's a switch or a toggle.

Review the schematic if you can - and re-check the values - for if any are too far off their banded values, it can force the op amp to work as a comparator switch than a linear audio amp.

Have you replaced C128 - Right by TR32? You might want to try a different LOWER value of 0.47uF Electrolytic for now, then bump it back up to 1uF once you have audio stable.

​

Why am I showing you R177, and R176 and R178 for the reason of you may need to LOWER the value of R177, or R178 - or RAISE the value of R176 - to lessen the IMPACT the ALC and AMC have on this circuit and then let the Audio DRIVE from the Mic amps' own output determine the limiter COMPRESSION level....

Ok, yes, I said that, COMPRESSION (R178) and LIMITER (R177, R176)

Your Mission - should you decide to accept it...

• determine the values you need to use in this realm of Limiter action and work accordingly.

Location of TR34 and D70...

​

Hope this helps someone...

 

[Handy Andy]

Ok - one last note on this...

Knowing that the R177 and R176 seem to work AGAINST each other...

Rethink the approach, or at least the location of this "R177, R176 divider situation"

Yes, Divider...

Go back to D70 - locate it, Locate R176, and remove it - place R176 in series with BANDED side of D70.

Form it like this...

​

D70 with R176, put it back in where D70 is.

Grab a 4.7K on up to 22K and put it where R176 was <<<-You select what value depending on level of audio you want the Limiter to clamp on...

You can also do this "trick" on the Compression side of the Limiter TR32 - the R178 - just "bump down R178" in value ranges until you achieve the 100% modulation realm - without severe clipping - then insert the other value of ALC AMC limiter action you wish - in resistor value.

This may mean you're lowering R178 to as low as 1K to as low as 820 (no lower else RX side affected) ohm - but this will quiet your receive and give you the limiter and compression action you wish.

Remember the limiter will Operate to QUIET your receive so that means R178 cannot be too low, for it can force D71 to blow open thru too much current - ruining the effect - so you will need something there.

I use R178, 1.5K (Brown - Green - Red)
D70 gets the R176 3.3K value IN SERIES with it
R176? (It's NEW Value) I've found 15K to 18K acceptable.(Brown - Green - Orange or Brown - Grey - Orange)
R177 kept that at 1.2K - leave for now...

It's the "aspect" of where the manufacturer places the dropping resistor - does the dropping resistor portion of the divider circuit become very important. In one light, it's a simple "Emitter load resistor" which then makes the follower resistor a simple buffer limiter, or current limiting resistor with all the impedance effects in full force into another stage with an input of high impedance but narrow linear admittance window in which to operate - affects performance of the Analog signal - treats it more like a digital type.

• This is what made me look back at the older 945AQ, 945C and other types compared to a 458 - both are NPN but their knee power curve and the threshold it operates in, is different

When you take a look at the schematic - the Dropping resistor that is the most effective is R178 - all the others simply keep the drive to the next stage operational.

What we did...

Move the Resistor that drops the current (the buffer location) to the position that makes the current drop the most effective - BEFORE the dropping resistor portion of the power flow.

​

The power flowing out of TR34, in the positions shown in original design - isn't restricted, just "buffered," We moved the "buffered" resistor from position of being the buffer, to the side from where the power TR34 has, still flows thru D70, then into R176's new position, and into the branch of this divider circuit BEFORE the divider R177 - versus after R177 then into R176 as the original design showed.

Which now frees up R176 spot to offer a more tailored restriction, you put in the value you see fit for the ALC and AMC to work effectively - now R177 influences the TR32 Limiter in a different more effective way.

EDIT:Cleaned up graphical images

 

[NODENS]

Thx Andy as always, something to learn in each of your post.

Some other ideas (if not checked already), bassed in experiences with some rigs:

• Did you check that VR14 is not "open" (is it within specs?). I had one rig in which, this pot was "open", i mean out of spec with a resistance much higher, and the symptom was the same, no modulation. Those pots tends to go bad with the years.
• Have you checked 8V regulator?, is regulating about 8.X Volts?. I had one rig with the Zener in that area bad, and my 8V rail was almost 9V, and i had modulation issues until i took that rail voltage back to its suppoused value.

Good luck!

 

[Handy Andy]

Hi @NODENS !

Thanks for stopping in - Radio seems to be stable, and works, just TR32 tends to clamp pretty tightly.

This problem is more common now than ever, so many an operator simply "removes" the Limiter and never enjoys the effects it can produce. At a former job, I was one of many techs that had to "fix" radio's that acted DOA out of the box, this was one of those specific part areas we have to fix as a Bench Test to show the customer a "profile" of the radio as a proof of operation for the sale. Like a blueprint of the ability for the radio to work.

So the newer discrete transistors seems to act more like Germanium by voltage drop performance but more like Carbide-based Silicon in construction.

Why? I can only guess, but IMO - The new "Discrete" seems to be more based upon Schottky design of junction - narrower Barrier (yes, you are correct, you cannot have a Transistor without the PN Junction) which also changes the Voltage Drop and the threshold On and Off voltages.

Great to have a fast high-speed switch, but if it's going into an older analog design - it needs tweaking of the "thresholds" in the Bias department to get the "knee" of it to work right.

The separate issue of Parts representation and location on schematic in the circuits versus their physical placement in the circuit which changes the expected performance and how the circuit works - it's a chronic issue as of late.

 

[26TW06]

Hey Andy,

right, where do I start? Well, I think I have got myself into a bit of a muddle I'm sorry to report.

I have done some of the things that you instructed. (bits that I haven't done yet, is because I need to source components).
Just thought I'd update you with the status so far!
Replaced c132 with new

Replaced R 178 with new 4k7 (tested the old one out of circuit and it measured bang on. This is the resistor which measured 2K2 in circuit).
Checked R179, measured over 3m

Checked the voltage at D84. It measures 7.somthing volts in USB, LSB and CW. 0v in AM, which I think is what's supposed to happen.

Replaced D84, D85 and D14. (I desolded D14 in error, so I decided I may as well replace with new, as it was out anyway).

D83 "Only other thing to check would be TR34...and D83 - works off of the 8 volt regulator and is a 2SA733, so its' BASE is applying power all the time - sends it thru D83 - into the two Audio Limiters - SSB ALC - TR47 and AMC Limiter DETECT TR53."

D83 in AM RX 5.45v. In TX it measures 3.96v at the banded end.

TR34 Base 6.26v TX and 4.59v RX. Manuel says it should be 8.1 and 8.0 volts.

"TX the Collector is going to 0.6 - still tells me it's making TR32 turn on enough - so we have to locate what or why TR34 is holding TR32 high. So I'm thinking that the Bias resistors R177 and R176 are doing this mess to you..."

Manuel says that R177= 1k2 and R176= 3k3

My R177 measures 1k. R176 measures 2K in circuit

"Have you replaced C128 - Right by TR32?" No not yet. I need to source a replacement.

Oh, I did check that VR14 is not open (thanks Mr Nodens). Cant recall now what it measured as, but I can confirm its not open or shorted.

Haven't change that value of the bias resistors yet, as I only have direct replacement values. I am am going to order some parts a little later today.

Cheers Darren

P.S: I noticed a very slight change in the symptoms post replacing some of the components. I now have a very , very faint bleep/peep when releasing the PTT in AM and FM. Whats more, USB and LSB also. The meter in TX also moves very, very slightly in the USB modes to indicate a transmission, but no more than the width of a human hair.
In CW, I can now hear the Bleep/peep through the radio speaker clearly when releasing the PTT. not sure if this is progress, or if it muddies the water further!

 

[Handy Andy]

When you see 8 volts on D84, that is part of the multiple pole of the MODE switch.

D84 should really not have any voltages on it for AM and FM - at least, on the UNBANDED side, Banded side? IT may, but at a function of TX mode (D72). So this looks like a mess of diodes that we'll have to track down...

D40 (10.695) handles the OUTPUT of D84, D85 COMBINED together - to turn on the 10.695 for SSB - when in that mode, D40 and D39 (TX MODE) BLOCK voltage from appearing on D84 and D85 (Steering power away - TOWARDS the 10.695 Oscillator) when the 10.695 is needed for the MODE its' in, you only see "voltage" appear on D84 and D85 when in USB or LSB, CW is thru D85

You said you see voltage there at D84 nearly all the time - it means we may have a wining or shorted mess elsewhere...

Let's verify D40 and D39 are good, they get power from - shall we make a list - perhaps it's best...

D40 - gets power from D84, D85 - USB, LSB and CW
D39 Gets power from TX mode.

So, no matter what - 10.695 works only in USB LSB MODE Live for D40 and D39 - D40's BANDED end will show power IN TX MODE CONDITION - not matter WHAT MODE YOU ARE IN.
In RX Mode Condition, d40 UNBANDED side Only USB/LSB and CW.

So both the Banded and unbanded sides of these diodes, we need to check to see if power flows from and thru them but not back behind them thru to their unbanded sides.

This requires lift and check method - PITA - but I think you already know this...

Since there are issues with TR32, check also - the BASE of TR52 (AM Inhibit) - it will reflect these voltages above - that same way, Its' purpose - in SSB and CW sends full power to the Finals by bypassing the Audio Regulation side of the AM Regulator - turns off the audio side and lets power go straight to the finals. No audio from Regulator - Pure DC. Another thing to check for at those Test points to help you troubleshoot.

 

[Handy Andy]

Sadly - this was supposed to a simple why not re-bias the Limiter to make it work again, at least it looks good in theory, but instead has cascades of "What if's" looming large - looking for Occam's Razor to appear and slice this to the bone...