Is this a common problem? Transmits great but receive is very low. I have a 139xlr with 858 board also. Is this common for these? Is there a fix for it and if so, who can do it?
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Sb520 low receive
- Thread starter David1dogg
- Start date
It sounds like an alignment would be needed, any reputable cb shop can do this. Avoid any additional mods offered unless it's a service bulletin, some places like to upsell useless or disastrous modifications .
You may be referencing another platform altogether. I believe the op is referring to the Robyn SB-520D radio.
Robyn SB-520. A CB AM/SSB base built only in 1978. Shares the same main circuit board with several brands and models of that year. Totally analog. No present-day sort of smarts to be found inside.
Two reasons to recommend alignment as a starting point. Adjustments drift with age, and it might need only for the tuning slugs in a handful of 10mm RF and IF transformers returned to their peak position.
There is also a risk that the capacitor built into some of those 10mm 'cans' has failed. This is easy to spot. While feeding a steady WEAK signal into the receiver, peak the receiver alignment point one by one. If any of the slugs appears to peak with the slug DEAD EVEN with the rim of the hole, make a note of that one and move on to the next step.
That dead-even-with-the-rim peak position of the thin slugs reveals a fault that will reduce sensitivity.
Could be that alignment alone brings it back to receiving properly. And if not, checking for the "dead even" symptom is the next-most likely failure to find.
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Two reasons to recommend alignment as a starting point. Adjustments drift with age, and it might need only for the tuning slugs in a handful of 10mm RF and IF transformers returned to their peak position.
There is also a risk that the capacitor built into some of those 10mm 'cans' has failed. This is easy to spot. While feeding a steady WEAK signal into the receiver, peak the receiver alignment point one by one. If any of the slugs appears to peak with the slug DEAD EVEN with the rim of the hole, make a note of that one and move on to the next step.
That dead-even-with-the-rim peak position of the thin slugs reveals a fault that will reduce sensitivity.
Could be that alignment alone brings it back to receiving properly. And if not, checking for the "dead even" symptom is the next-most likely failure to find.
73
Was there a small transistor that was prone to failure on the receive? I have to dig out what part it was. I think there was a service bulletin for it for the 138 XLR radios, but think that one of yours uses the same board. Symptoms include bad reception or no RX at all. TR5 is the one on the 138 XLR boards.
if I remember correctly, TR5 is next/around the area of the small transformer on the back.
if I remember correctly, TR5 is next/around the area of the small transformer on the back.
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Maybe not today, but if it comes outta nowhere someday, then it might be.
Aside the aging old capacitors, I had a 138 XLR that at first I thought it was TR5, but then soon learned the actual audio chip was dead in the water. 
Once that got repaired, it was making an aweful screeching sound when the relay would click on to transmit. Turned out it was a loose chassis screw near the back underneath. Tightened it up and it went away.
The whole folklore of "known" issues is mostly relevant the first 20 years of the radio's life. When it gets to be closer to 50 years, it's best to expect multiple faults. A quick "known" fix for troubles in a radio that old is probably a vain wish. When we replace all 50 electrolytic caps in that generation radio it may just straighten up and fly right, or it may still exhibit additional faults. Until you go to the expense of recapping the radio, nobody knows.
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