Just got finished working on an old Galaxy Saturn (ept3600 board) that had some receive issues.
AM receive was ok, not the best in the world.
AM meter had to be cranked almost wide open.
SSB receive was weak, it was there but volume had to be turned up halfway just to hear people.
SSB meter movement was almost non existent.
Checked alignment, only came up a little, not much. Recapped entire radio then checked alignment again, touched up the alignment, again just a little better.
Checked all IC voltages, all checked good.
Checked all diodes in the receive and SSB circuit, replaced D15/D16, slight improvement, SSB still not up where it should be.
Checked all transistors. All checked fine except for some strange readings from TR20, TR21, TR22, so I yanked them and tested them, they all tested great.
Ran through the block diagram again and noticed TR19, which I haven't checked yet. Voltages were weird, and one lead that should have had voltage on it was actually showing 0v.
Yanked out TR19 and tested in the tester, it tested as a diode. Reseated it in the tester and tested again, still tested as a diode. Tested it a third time just to be sure, yep, still tested as a diode.
Soldered in a new one, checked alignment, BAM!!! Beautiful receive on all modes.
SSB meter was still goofy though. I first checked the transistor part number and compared to the parts list for that spot. This transistor looked brand new is why I suspected it, and sure enough it was the wrong transistor for that spot, it was a 733. Replaced the 733 with a 945, bingo, SSB meter is back to working as it should. The transistor location on the board for this SSB meter is TR14, it's right in front of the SSB meter adjustment VR.
Tip:
If you ever run into this issue, then check TR19. It's a 1674, then realign the receive. TR19 is just to the right of the large silver SSB crystal filter.
Another tip:
Always check those transistors out of circuit also, so as not to get false readings due to other nearby parts in the same circuit.
Another 35yr old Saturn ready to rock-n-roll like a brand new one.
AM receive was ok, not the best in the world.
AM meter had to be cranked almost wide open.
SSB receive was weak, it was there but volume had to be turned up halfway just to hear people.
SSB meter movement was almost non existent.
Checked alignment, only came up a little, not much. Recapped entire radio then checked alignment again, touched up the alignment, again just a little better.
Checked all IC voltages, all checked good.
Checked all diodes in the receive and SSB circuit, replaced D15/D16, slight improvement, SSB still not up where it should be.
Checked all transistors. All checked fine except for some strange readings from TR20, TR21, TR22, so I yanked them and tested them, they all tested great.
Ran through the block diagram again and noticed TR19, which I haven't checked yet. Voltages were weird, and one lead that should have had voltage on it was actually showing 0v.
Yanked out TR19 and tested in the tester, it tested as a diode. Reseated it in the tester and tested again, still tested as a diode. Tested it a third time just to be sure, yep, still tested as a diode.
Soldered in a new one, checked alignment, BAM!!! Beautiful receive on all modes.
SSB meter was still goofy though. I first checked the transistor part number and compared to the parts list for that spot. This transistor looked brand new is why I suspected it, and sure enough it was the wrong transistor for that spot, it was a 733. Replaced the 733 with a 945, bingo, SSB meter is back to working as it should. The transistor location on the board for this SSB meter is TR14, it's right in front of the SSB meter adjustment VR.
Tip:
If you ever run into this issue, then check TR19. It's a 1674, then realign the receive. TR19 is just to the right of the large silver SSB crystal filter.
Another tip:
Always check those transistors out of circuit also, so as not to get false readings due to other nearby parts in the same circuit.
Another 35yr old Saturn ready to rock-n-roll like a brand new one.
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