EPT360010A - Saturn SSB

[Hawkeye351]

Well, I don't have any 50pf trimmer caps, but I do have an assortment of pf caps. Tried multiple on L14 outer 2 pins on the 3 pin side of that IF can.

I tried a 33pf, 39pf, 58pf, 60pf, 69pf and 82pf.

Tried each one, realigned that circuit, tried the next value, realigned that circuit, etc...etc...

Came out with best result using the 39pf, with slug down about 4 turns below top of can.

All receive came up, still somewhat weak, but a lot better than it was.

 

[Hawkeye351]

Correct me if I'm wrong, but if I was to try other values between 0pf up to 50pf then I could probably get a better result, right?

And, the reason it's still somewhat weak is because the value I currently have in place is close but not quite the value needed?

The closer I get to the right pf needed, the better the result will be?

1 and 2 are pretty much the same question, just in a different form.

 

[Hawkeye351]

Checked it out just now with my locals since skip died down.

Results:
Sideband receive great, xmit great
AM receive weak but slightly better, xmit great.

AM just seems dead on signals past 7 miles away, but up close strong signals, or strong skip sounds good.

I have several guys out here using radios I aligned to help with reports on this radio specifically. They're rooting for this old classic to be back up and running after years of not being used. I mention y'alls names a lot to them of how much help you all have been in this rebuild.

I may not do another one, lol...to much trouble, but I love these classics.

Thank everyone that helped out by pitching in with tips, advice and detailed info, your help is greatly appreciated.

If I was charging for this work, harassment, lol, I'd be rich by now.... The barter system has never failed me so far.

 

[nomadradio]

Came out with best result using the 39pf, with slug down about 4 turns below top of can.

Very cool! Contratulations for sticking with it.

I don't have the patience to try more than one fixed cap. I keep enough trimmer caps on hand to just grab one when needed. Sure would be nice if someone (else) worked out this value for the rest of the radio's IF/RF cans.

73

 

[Hawkeye351]

Ok, I think I've found an issue:

TR30 has no voltage on it at all in receive.
Removed TR30 and tested in tester, stated hfe of 275.
Removed D84, checked on tester and multimeter, shows good.

Tr1, tr2, tr3, tr4, tr5, tr6, tr7, tr8, tr9, tr10, tr11, tr16, tr17, tr18, tr19, tr23, etc...all check out fine on voltage.

Gonna have to back trace I guess.

 

[Hawkeye351]

Aha, found my issue, there is no 8v present on the line coming from the mode control to the board.

I traced down the supply to D84 at the terminal bus. It's the green wire coming from that spot up to the mode control that feeds D84 the 8v needed. But where'd it go? Lol...

Any ideas guys?

 

[Hawkeye351]

Got it, omg this thang drove me nuts, lol...

Guess I need a good source for the 455 filter FL1. I had replaced the original FL1 455 filter because it looked as though someone had been poking at it with a hot tip of a soldering iron. I replaced it with one that came out of a galaxy dx 33hml.

Well, after another round of checking transistor voltages, I noticed I was missing some from that filter, so I replaced it again, then turned it on and BAM, the AM receive is back and loud.

Either the galaxy 33 hml filter was bad or that filter won't work in this ssb radio.

Receives great and loud in all modes now.
Transmits great in all modes.
All functions work as they should.

Pretty much completely rebuilt main board.
Several new IFTs.
New 455 filter.
New 10.240 crystal
Several new transistors.
Several new germaniums.
Several new zeners.
Few resistors replaced.
2 New ICs.
3 New control pptentiometers.
New FL2 filter.
All electros replaced.
Few pf disc caps replaced.
New passthrough reg.
New AF reg.
New 8v reg.

Whew, glad this one is over.

Thank you all for the help.

 

[Hawkeye351]

This radio is gonna be the death of me.

Got the receive working great. Just now noticed I have a 6w carrier on both side bands. Checked carrier balance, it's fine. It's not squealing, even with mic gain turned all the way down it still shows a 6w carrier on both side bands.

Only way to get it to drop is crank the driver bias all the way up, both final bias pots are almost completely turned down. But then there's not much output. With the bias adjusted at 30ma driver and 50ma on each final (totaling 100ma), then I get full output, bout 40w in all modes, but then I have a 6w carrier on both sidebands.

I changed out the 2.2uf 50v cap next to the passthrough cause that transistor and cap would get scorching hot when in sideband. Still same results. Swapped out passthrough and AF regs again, same thing. Removed the diodes strapped across each final and put some others in place, same thing.

I'm lost now, broke my heart. I was proud of what I accomplished.

 

[Hawkeye351]

Well, just checked the bias VR pots with the multi meter.

VR11 should be 1k ohms (stamped 102).
It measures at around 987 ohms.

VR20 should be 100 ohms (stamped 101).
Measures at around 11 ohms.

VR10 should be 100 ohms (stamped 101).
Measures at around 10.5 ohms.

 

[Hawkeye351]

Why is it I could set the bias with the factory VRs before, although the final bias adjustments I could barely crack them up from 0 to 50ma? Just barely nudged from 0 it would go to 50.

 

[Hawkeye351]

Just yanked out both bias VRs for the 2 finals.
This was done with both VRs turned to their lowest stop.

Touching outer 2 legs, (not wiper) of each shows:
153 ohms, the other 137 ohms.

Touching wiper and one outer leg shows 153 ohms, whereas touching the wiper and the other leg shows 23 ohms on one.

Touching wiper and one outer leg shows 137 ohms, where's touching the wiper and the other leg shows 17 ohms.

Whereas the 2 new ones show different when touching the outer 2 legs, they show:
97.6 ohms, the other 92 ohms.

Touching wiper and one leg shows 97.6 ohms, whereas touching wiper and other leg shows 2 ohms.

Touching wiper leg and one leg shows 92 ohms, whereas touching wiper and other leg shows 1.9 ohm.

So, do the original final bias VRs seem shot?

 

[Hawkeye351]

When the xmit issue started, I remember hearing a snap noise (like breaking a toothpick) in the final section. I unkeyed and looked that way, saw a small light stream of smoke briefly around the last final, didn't last long enough for me to catch exactly where it came from. Plus there was a slight smell of plastic or ceramic. Then is when it started this mess.

Checked all 3 finals out of circuit, all checked good with multi meter testing and transistor tester.

3 diodes across finals test good out of circuit on both multi meter and tester.

Replaced passthrough again. Replaced AF again. Replaced 5 electro caps in passthrough section again just for cautionary measures, although the ones pulled out were still new, because I replaced all electros in that section before anyway.

The tuning slug at the final is having to be bottomed out now to get 35w am/SSB, but still exhibits a 6w key on both SSB with mic and gain turned all the way down. Carrier balance has no affect. Radio sounds great though, on all modes, no noise or anything, just loud audio. The regulator/IC side does start getting hot within about 30 seconds though.

L42, L43, L44, etc...in the output stage make very little difference, or dramatically jumps up and down.

I've also noticed, never really focused on it, but every time I touch the radio, or get near the inside of the radio with my arms, the output on the watt meter, waveforms on scope change significantly? Sounds like a ground issue somewhere right?

Hmmm, this one, lol...

 

[Hawkeye351]

Replaced those 2 bias VRs in front of the finals with the good ones. Same result.

Then I went to check bias on driver and it goes from 0.69a up to 2.09a, won't go any lower than 0.69a.

Hmmmm, the driver bias VR tested good, what the crap, lol...

Still curious about that snap in the final section I heard when this issue started.

 

[Hawkeye351]

Removed:
C165 - 571pf
C166 - 563pf
C167 - 150pf
C170 - 561pf
C211 - 44pf
C159 - 12.31nf vlose=0.8%
C216 - 43.20nf vloss=0.2%

Hmmmm....do the last 2 seem right?
All resistors in that same area look and check out within range.

 

[nomadradio]

curious about that snap

One of the bias trimpots as it burns and becomes an open circuit? Don't know. A noise like that should leave some visible trace of the event, you would think.

Unless I missed something the capacitors look okay. C159 and C216 are bypassing caps, connected between circuit ground and chassis ground. The acceptable error tolerance of this part is a lot wider than the rest of that list.

When replacing a final in these radios I learned the hard way to leave the base terminal unsoldered, sticking straight up away from the pcb foil pad. A quick check of the voltage on that pad served to prevent poof problems from excess DC base current from the bias circuit. A reading on that pad much over 6/10 of a Volt is a hazard to the transistor. Fixing that first saves on toasted finals. The bias circuit in these radios is highly vulnerable to surge from a failed final, and if it runs away the new final overloads and toasts before you can react.

The 1 ohm resistor with the ferrite bead on one leg is a frequent casualty when a final fails.

73