Galaxy Saturn receive...

[Hawkeye351]

Got a galaxy Saturn on the desk.
Issue is, slightly weak receive on AM, almost non existent SSB receive.

Checked RF Gain and Squelch controls, both function properly and smoothly.
Checked RF Gain trace from RF Gain control down to TR17, everything looks good.

Replaced,
C19
C20
C35
C40
C31
C32
C333
C44
C122
10M04DS SSB Crystal filter (FL3).
10.240mhz crystal was registering as 9.89mhz. Replaced with known working one, still it's at 9.89mhz.

Checked voltages on all trannies in the receiver and oscillator sections, all check good except for TR24 (PLL Reference Oscillator). TR24 shows the base and emitter as right, but the collector shows only 3.24v in any mode, when it calls for over 7v.

When adjusting the 3 carrier offset oscillators, the frequency is very erratic, very sensitive adjusting to get the right frequency. Once you get below 10.6935, then it goes haywire. If you get above 10.6977, then it goes haywire. Although the sideband signals I do pickup faintly, sound exactly on frequency. AM volume is way louder than SSB volume. AM receive signals are all 2db down, before and after alignment, but sideband is almost non existent. You have to turn volume all the way up on SSB. When you flip back to AM then you have to turn volume down to around 9 o'clock position.

Also hardly any SSB s-meter movement.
Any suggestions guys?
Would the FL1 Crystal filter (455) cause this?

 

[Hawkeye351]

After looking over the voltages I should see on TR24, comparing it to what I'm actually seeing on TR24 in any mode.

Also, after following the schematic and block diagram revolving around TR24, what's tied in with TR24.

I'm thinking a disc cap or electrolytic in that general area is the problem of my collector voltage being only around 3v on TR24 when the chart calls for over 7v.

This, I also think could be my problem with the 10.240mhz crystal showing 9.89mhz on pin 4 of the PLL, since the mixing crystal ties in with TR24.

This, I also think could be why receive is down, since TR24 ties in with the mixer stages in the receive section, 1st mixer, FL1, on down the line to the SSB detector.

Guess I'll replace C82, C89 and C90. Then if still the same issues, I'll swap out TR24.

 

[nomadradio]

Saw a lot of bad 10.24 crystals in the mid-1990s Galaxy radios. Found myself selling as many in a month as I was used to selling in a year. The crystal's leads were held in place by a brown resin of some kind. That particular batch of bad crystals came and went. They hired a new vendor who used an all-metal crystal case with the lead wires held by a tiny circle of glass. That cured the problem for the most part.

73

 

[Hawkeye351]

This one was the good one I guess, lol, replaced it with another good one, which I know is good, but the frequency was still showing 9.89mhz instead of near the 10.240mhz off of pin 4 of the PLL.

According to the schematic, pin 3 of the PLL is tied in with TR24 collector lead. The voltage chart for the PLL pin 3 shows a little over 3v (which mine shows also), whereas the voltage chart for the collector of TR24 should be over 7v. Which my collector of TR24 shows the same voltage as what pin 3 of the PLL should be/ and is.

Not sure if this big of a difference in the 10.240mhz being off that much would affect the receive this much in ssb though.

The carrier offset oscillators range (all 3) is only between 10.6924mhz up to 10.6978mhz, then they go all haywire. I figured the 10.695 crystal was bad, so I changed it, with no improvement. It's a pain in the butt adjusting these 3 oscillators on this radio.

VCO voltage adjusts fine, got it set to 3.20v on AM channel 20.
VCO buffers adjust fine, got those maxed out, as usual on these rigs.
PLL synthesizer offset oscillators adjust fine, smooth adjustment.
RF stage adjusts smoothly, no issues here.

Just the 10.240mhz signal showing 9.89mhz on pin 4 of the PLL instead of 10.240mhz or closer to it.
And, TR24 collector voltage being over 3v instead of over 7v like the chart calls for.
And, why the carrier offset oscillators are so touchy.
And, why SSB is so much lower (almost non existent) than AM (which is slightly lower than it should be).

Also, I noticed that when turning RF Gain up and down, when you turn from lowest up to 12 o'clock there is no change, just silence. But once you go over that 12 o'clock just slightly then then receive snaps in (like flipping a switch). From that point up to max position, the receive comes up, but not up as high as it should be. I shorted out the proper flanges on the RF Gain control with gain turned wide open and noticed no change in receive. I then placed the red probe of my volt meter to the flapper of the RF Gain and the black probe of volt meter to electrical ground and the voltage did go up and down from 3.28v with gain turned all the way down, to 0.00v with gain all the way up, with no erratic changes while turning RF Gain, smooth voltage changes. I then checked the RF Gain control through TR17 and did get smooth voltage changes there also.

I haven't touched it since, been trying to think the circuit over. May just replace all the 10v, 16v caps in the receive, Oscillator and VCO sections. That'll eliminate those as the issue. Since the FL1 filter is in line with TR24 collector lead, could this filter also affect SSB receive, but more than AM, and the voltage difference on the collector of TR24?

 

[Hawkeye351]

Testing RF Gain through TR17:

Base:
RF Gain up = 2.12v
RF Gain down = 2.17

Collector
RF Gain up = 7.87v
RF Gain down = 8.01v.

Emitter
RF Gain up = 1.42v
RF Gain down = 3.28v.

From TR17 voltage chart (from cbtricks for 99v):
Base - 2.20v
Collector - 8.00v
Emitter - 1.50v

 

[Hawkeye351]

Well,
Finished recapping. Replaced all 10v, 16v, 25v caps with new Nichicon types. The 50v caps I didn't replace, their esr and values were still within range. Most of the 10v and some of the 16v caps had very high esr on them, and some would constantly fluctuate readings when testing for values. All the new caps tested with stable values and low esr.

Result:
Got the 10.240mhz signal back close to the proper reading, it's now showing as 10.239mhz and fluctuates back and forth from 239 to 240 very fast.

AM receive is great, SSB receive still low.

TR24 collector voltage is still over 3v instead of the voltage the chart calls for, which should be over 7v.

Transmits great and on frequency at any power level, runs cool, sidebands transmit great and on frequency, get great signal and audio reports on it.

All IC voltages check good, all transistor voltages check good except TR24 collector, all resistors are within tolerance, nothing gets hot.

Replaced so far:
L13, L14, SSB filter, all electrolytic caps except 50v caps, D24, no mods in this radio whatsoever.

Since I replaced all the electrolytic caps, I don't have to turn volume up to halfway to hear sideband signals anymore, I now have to turn it up to only about the 10 o'clock position, AM receive volume stays around the 9 o'clock position. Maybe we just dead on SSB in my area right now, even my FT-950 on a flat side wire is quiet on SSB. But I'll check it again tomorrow and let y'all know.

 

[brandon7861]

TR24 collector voltage is still over 3v instead of the voltage the chart calls for, which should be over 7v.

If a typical crystal oscillator has between 1mA and 10mA of collector current, there would be a minimum of 1v drop across each resistor (R110, R120 and R121) for the 1mA case (since they are 1k resistors). On an 8v regulated supply with those resistor values, to have over 3 volts on the collector means under 2.5v across each resistor north of the collector. The oscillator is currently running at just under 2.5mA, and that, as far as I know, is well within reason.

Edit: for reference, with 7v on the collector, that leaves under .5v across the two 1k resistors. That would put the oscillator at 0.5mA, and I think that might be too low. I am suggesting the chart might be wrong.

 

[Hawkeye351]

Guess the SSB receive might be right, won't know for sure until I hear some ssb coming in on my 950, then compare that receive somewhat with this receive.

I know if I'm on AM and scan across 39, 38, 37 I can hear ssb stations strong rumbling AM, but when I flip to SSB, the signals are very low and not that strong, as AM was making it sound.

Just gonna keep at it. Gotta be a disc cap or diode in the circuit somewhere limiting ssb receive while allowing AM receive to work properly.

Like I said, AM receive is about normal now, constant 3 s-units of hash noise (which will fall to about 1 s-unit the later in the night it gets) on all channels, the AM s-meter is adjusted to about the halfway mark and I receive the proper signals as usual on all my locals, even distant locals I know.

All oscillators adjusted smoothly this time, the VCO voltage is adjusted to 3.20v for channel 20, the buffers adjusted smoothly and maxed out, all VRs adjusted smoothly, all IF receiver cans adjusted smoothly, none of the cans are topping out flush with the can, although one in the receiver stage is almost bottomed out for the receive to come in like it is now.

Not sure what's the problem with SSB receive. Gonna keep working at it.

 

[Hawkeye351]

Hmmm,

just checked TR52 SSB Switch voltages again. This time I switched back and forth between AM/FM/USB/LSB while monitoring voltage on each pin. The Base is exactly what's called for in all modes. The Emitter is correct in SSB mode but shows around .80v in AM/FM modes. The collector is correct for SSB, but doesn't drop in AM/FM mode, the collector voltage doesn't change at all from SSB to AM/FM.

TR52, C193, R243, and two 10k ohm resistors next to R243 get extremely hot (so hot you can't touch them) within 1 minute of flipping to either SSB. In AM/FM those parts cool off drastically.

Note: the voltage on the mirror board (bias) in AM shows around 5.65v, in SSB the voltage on the mirror board (bias) shows over 13v.

 

[nomadradio]

Is the slug in either L13 or L14 have the end of the slug dead flush with the rim of the hole?

If so, this indicates that transformer is not resonated. Would hold back SSB sensitivity, wouldn't affect AM.

73

 

[Hawkeye351]

Both L13 and L14 both peak around 2 full turns down from the top, not flush with top.

L8 almost bottoms out just to get the receive in. Maybe an issue.

All other IFT's (silver cans) peak between 1.5 full turns to 2.5 full turns from the tops, not flushing.

 

[Shadetree Mechanic]

I believe L8 goes to the stage with the double FET transistors. Maybe one of them is bad?

 

[Hawkeye351]

Changed a few more parts that seemed suspicious this morning.

Changed L8 with a known working one of the same value. No change, I had to almost bottom this one out to for receive to peak.

Changed C17, very little improvement in SSB receive.

Changed C67. No change in results.

Replaced TR52 and C193. No change, all parts in this area (TR52, C193, R243, and two 10k resistors beside R243) still get scorching hot within a minute of switching to SSB. So hot you can't touch them.

Although it could just be another case of no SSB cause of no conditions. Even my FT-950 is almost dead as far as SSB receive goes.

When I do hear SSB stations, there is no meter movement at all. Even when I hear a loud station on SSB there is barely any signal movement. That's with VR2 turned either wide open or all the way down, obviously the meter will drop when I adjust VR2 down and comes up when turning wide open. I got VR2 turned all the way up just to get some kind of meter movement. Now a local strong SSB station will move the meter, but only to half scale. AM/FM has no issues at all, and transmit has no issues at all, even in SSB mode. Everything else on this radio works beautiful, just SSB receive is lower than AM/FM receive. Oh, and parts around TR52 get scorching hot within a minute of switching to SSB. That's the only 2 issues plaguing this radio.

 

[Hawkeye351]

I know TR18 is one of the FETs you're referring, but which is the other FET?

TR18 voltages are correct according to voltage charts. And it's placed in the same orientation all these export radios have TR18 placed, backwards from what the silkscreen on the board shows.

 

[Hawkeye351]

Replaced FL1 (455 filter), no change.
Replaced C89, no change.

Aligning the SSB receive with the RF generator goes smoothly, everything goes great, but not when hooked to an antenna. Antenna is the same antenna I always use with no issues ever, SWR is 1.1, all jumpers and coax are tuned lengths. If the antenna was to affect ssb receive, then obviously it would also affect AM/FM receive, along with transmit, but AM/FM receive and transmit in all modes is great.