EPT360010A - Saturn SSB

[Hawkeye351]

Still got this Galaxy SSB Echo Base I'm trying to figure out.

Got the mic audio issue straightened out, mic gain control was bad.

Receive audio still low. Volume control does affect volume. RF gain does bring receive up and down.

Just receive audio weak. Replaced audio IC due to bad test results. Replaced passthrough reg, AF reg, 8v reg.

I did probe the RF Gain control and got 3.3v all the way up and .74v all the way down. Removed center wire (grey) and top wire (orange) and tested those wires and got 7.74v. Replaced L6, still the same. R56 and R55 look fine. I feel it's in the first IF section somewhere.

Shaking radio has no effect,
Shaking/wiggling wires has no effect,
Flexing board has no effect,
Fiddling with parts has no effect,

If I key up nearby monitor radio with RF Gain wide open and volume wide open it pegs the meter and squeals, if I leave volume up and turn down RF Gain then the received keyed monitor station drops out as it should. Like the receive is too low, but all controls are working.

This is all I got left on this radio. I thought I had it, but after hooking to antenna, it only gets strong nearby stations, others are weak and low.

 

[Hawkeye351]

Back on this one again...

Still same issue, volume control works as it should in and out of circuit.

Rf gain works as should in and out of circuit.

3 wires feeding RF gain pot:
Black - ground
Grey - flapper
Orange - feed

Orange wire has constant 8v

If I remove all 3 wires from the RF Gain pot, and tap the grey and orange wires together then the voltage drops to 3v on those wires together. RF control pot itself varies when turned from 0 ohms up to 1k ohms.

Checked voltages on tr17 with RF Gain all the way up, voltage is around 3v on 2 legs of tr17 and 0 volts on the other. Turn it all the way down and and those 2 pins drop to 1.5v and the other stays at 0 volts.

Removed R66, checks at around 1k ohm.
Removed D15 and D16, both check as zeners and good.
Removed TR17, checks good with hfe of 73.

Curious as to why the 8v orange (feed) wire drops to 3v when connected straight to the grey (flapper) wire. Like something is shorted and preventing the 8 or 7.5v from getting to the receive section.

Note:
I did replace L6 quite some time ago with same results. I just replaced it to rule it out. I also had to replace the 7222ap ic due to it being bad. I also replaced all electrolytic caps on the right side of the board (passthrough section all the way up to the mic amp, from front to back.

Finals are good, great xmit, no issues at all with xmit or frequencies.

I'm stumped, could use some guidance.
Thank you in advance.

 

[nomadradio]

So the question remains. Is the receiver's RF/IF section weak, feeding very little audio to the volume control?

Or is the audio coming out of the mode selector switch okay, but one or more audio stages downstream of the volume control are what's weak? S-meter activity can be a help with this question.

Did you have a look at pin 9 of the TA7222P audio chip? DC voltage should be close to one-half the power supply feeding pin 1.

This is the kind of task where a 'scope pays for itself.

73

 

[Dr. Frankenstein]

This sounds very familiar from last year...

You didn't state if the problem was in AM, SSB, or both.

The voltages that you see at the wiper of the RF Gain are correct. Resistor R95 (1.5K) and the RF Gain (1K) form a voltage divider. Then R65 and R66 form another potentiometer that is locked, picture the point where they meet as the wiper that can't be moved to keep the proper voltage going to L6.

As I said in my last response to this problem back in November "Your problem is beyond L6", either a bad component or the "receive circuit" needs to be adjusted properly. If the receive circuit is adjusted and the problem is still there try changing FL3, I had an AR-3500 that did the same thing, one of the cap wires inside the potted filter broke causing a low receive. Found it using a scope, the scope showed the signal before the filter but very low after!

Don't keep getting blindsided by the RF Gain that is working properly. You need to understand how a voltage divider works.

Like nomadradio said a scope would help.

Let us know when it's fixed, I've been waiting for you to respond to this, but I'm sure with all the holidays getting in the way........
after all, we all have a life besides the radio.

73

 

[Hawkeye351]

Will do a complete alignment again and go from there.

Yes, ssb is the same as AM.

By the way, I noticed this mess on the bottom side of the board, it's not shown on the schematic or service docs.

Anyone know what this is all about? This mess could be my whole problem, just not sure of its purpose:

 

[Hawkeye351]

The circle in the center of the board is a combination of a disc capacitor, diode and resistor.

The circle near the pll is a combination of the same.

Here is maybe a better pic.

 

[Hawkeye351]

Oh, and I do have oscopes, 3 actually. One old school 100mhz analog and two 100mhz digital scopes. Along with an agilent 4411b spectrum analyzer.

I've been using just a volt meter to check voltages. Do you recommend using an oscope for voltage checks instead? Sorry for sounding stupid

 

[Hawkeye351]

I don't get it, unless this radio just has a quiet receiver by nature.

Checked the 7222 again, all good.
Checked 8v reg. again, all good.
Checked other areas, all good.
Checked pots again, all good.
Realigned completely, all good.

Receive audio still is quiet (with hash noise), but seems to receive fine.

Guess it's just a naturally quiet receiver.

 

[Hawkeye351]

Well, just hooked it to my antenna.
Both sidebands have great receive, even with volume turned down.
Made a few contacts on sideband, works great, they say it sounds great.

But on AM, the receive is very weak. Have to put my ear up to the speaker with volume all the way up to hear stations further than 7 miles away. If someone closer keys up I can hear them fine with volume all the way up but I have to back away from speaker. Everyone said it sounds great on xmit, no issues with xmit.

Does this sound like something to do with the AM detector circuit?

 

[Handy Andy]

This may be something with the AF preamp - the SSB side mixes the VCO and IF together and the product is the audio.

So you have a receive there, means the AF preamp is functional.

The AM side though - gets it's kicks from the detector so it may need a new one (Germanium types) - but you also need to make sure the Mode switch is sending power to the switching transistor (in 11Z and up it's TR23) to ground one of those diodes to help complete a circuit in the detector - so the detected audio current present can get to the AF preamp.

It uses the same "Audio Tap" from the SSB side - only it doesn't see any IF it is quenched off by having 8V applied in power to one side of a cap to act as a block to keep IF away.

(If you are following along at home - check out a Galaxy 88 - C72 and C74 and D 14)

That may be where your "mods" you show is at, these send the AM signal to the AF amp and some of it's sampled for the AGC so it can track the swing in the envelope, so the audio doesn't distort.

 

[Dr. Frankenstein]

Your pictures didn't come out that good, if you are using the flash on the camera try it without the flash. The Orange jumper near the PLL, I believe, is the Band Mod..... can't really make it out from the glair and is slightly out of focus.

Before you go any further, have you tried to tweak L16 to see if the receive comes up? L16 is in the synthesizer circuit and it is supposed to be adjusted with a scope, but if you are careful and remember where it was set before you touch it, the sound may come up, but should still be adjusted properly by the book. Again this is part of the alignment process if you didn't do a complete alignment yet. This problem could even be due to bad electrolytic caps.

About the scope use, it's used for watching the signal pattern as you follow it along the circuit, using the schematic to know where to go. You are tracing the signal pattern until it drops off, that is the point where the problem is. From L6 the output may be low due to not being amplified until after TR17 output, then L7 output, and so on...always looking at the output pattern following each circuit with the scope. Note that L12 has two outputs, one for AM and one for SSB, if the pattern drop-off hasn't happened after L12, then you'll have to go further. Remember when you had the volume problem and went nuts blaming everything else until I said to follow the signal to find the audio at pin 4 of IC4 and it wasn't there, then you found the volume pot was bad? It's the same thing but now the scope has something for you to look at and possibly locate the problem, don't worry about the voltage watch the pattern.

73

 

[Hawkeye351]

Voltages on IC1 checked out right,
Voltages on IC8 checked out right,
Voltages on IC4 checked out right,
Replaced C35 (ESR was 11.9ohms, too high for 47uf 16v), replaced when recapping but must be a bad one in the bunch.
Replaced C17
Replaced D23, D24, D25
Replaced C44
Checked C47, C48 and C49 for proper seating, solder.

Hmmmm, bout to pull my hair out on this one, lol...

 

[Hawkeye351]

Thank you Andy and Frankenstein for popping in, this thang could use all the minds together, hahaha...

L6 adjusts great for SSB, along with the rest of the receiver adjustments.

Someone 7 miles from me showed a good signal on receive on both SSB modes, audio and signal. SSB receives great. But when we went to AM, his signal on receive was non-existent and the receive audio drops dramatically. Although a nearby station about 3 miles away on AM showed about a 5s unit and audio still low with volume wide open.

Just the AM receive is driving me nuts. L6 and the other receive adjustments have very little affect on bringing up AM receive, but they affect SSB receive a lot.

Gonna try replacing the detector diodes again.

 

[nomadradio]

I recognize the mess under the PLL chip. It's a 8-Volt zener diode. The foil path that would feed 9 Volts into the chip gets cut, and a current-limiting resistor added across the gap. The zener is just lap-soldered to the foil pads for the PLL pins 1 and 18.

I'm not sure what kind of problem they were trying to solve with this patch. I have seen more than one radio where the foil trace was not completely cut through. Causes the zener diode's current to go through the roof. The zener gets RIGHT warm this way. The baffling part is how long the radio will operate this way, being cooked by a kamikaze zener diode. Typically melts all the wax on the top side of the board around this spot. The melted wax runs onto the solder side and drips off.

Later versions of the 3600 boards just feed 9 Volts straight to the PLL, no chaser.

Don't know about the patch in the center of the circuit board. Can't really make it out.

 

[TM86]

I'll start this off with I don't know jack about this radio. Never had one, never worked on one. I pulled the schematic from this thread: https://www.worldwidedx.com/threads/ept360010a.219935/

Looking at that schematic and the symptoms described here (bad AM receive, SSB OK). It looks like when switched to AM mode a voltage gets applied to the base of TR23, which should turn that transistor on. This happens in only in AM, so it would appear to be a logical place to at least take a look at. If there's no voltage through the mode switch, or the transistor isn't working, or something a little past that transistor is dead, seems like that might a problem.

My apologies if you've already checked that. Didn't see anything in the thread about it so I thought I'd throw it in. Then again, maybe I'm looking at the wrong schematic. Not like I'd know the difference.