Robyn 520D problems

[Deleted]

OK. Good new is that this appears stock. Now I have 2. One hacked and one stock, so I should be able to make one good radio.

This stock unit I just got has a few problems.

1. Power switch is bad (not a problem as I have spare).

2. No AM or USB TX or RX

3. LSB has TX, but no RX.

4. Channel display is flickering (regulator?)

The 13.8 VDC is solid. There is still a tantalum cap in the infamous C179 spot.

Before I dig in, let me know if you have any ideas. I am using a Cobra 139 XLR schematic.

[Deleted]

Scratch that. I now have receive, and I am working on TX.

[Deleted]

OK. I seem to have this working correctly. So I will likely recap it and clean it up. It is stock.

I still have a problem with a flickering channel display. Would this be a regulator? If the 8V regulator weak on this radio? If so, should it be replaced and with what?

[Sandbagger]

Dec 13, 2011 9:34:23 GMT -5 @vinnies said:

OK. I seem to have this working correctly. So I will likely recap it and clean it up. It is stock.

I still have a problem with a flickering channel display. Would this be a regulator? If the 8V regulator weak on this radio? If so, should it be replaced and with what?

Flickering how? A few segments or the whole display. Most often I see older radios with flickering segments, which turnes out to be a product of dirty channel selector switch contacts.

If I remember correctly, the display has its own regulator (actually a TO-220 case transistor) bolted to a heatsink, but if the problem isn't dirty contacts, a check of the display voltage is in order.

[Deleted]

Dec 13, 2011 9:50:36 GMT -5 Sandbagger said:

Dec 13, 2011 9:34:23 GMT -5 @vinnies said:

OK. I seem to have this working correctly. So I will likely recap it and clean it up. It is stock.

I still have a problem with a flickering channel display. Would this be a regulator? If the 8V regulator weak on this radio? If so, should it be replaced and with what?

Flickering how? A few segments or the whole display. Most often I see older radios with flickering segments, which turnes out to be a product of dirty channel selector switch contacts.

If I remember correctly, the display has its own regulator (actually a TO-220 case transistor) bolted to a heatsink, but if the problem isn't dirty contacts, a check of the display voltage is in order.

Seems mostly segments. If there any way to get at the internals with Deoxit?

[Sandbagger]

Dec 13, 2011 17:24:41 GMT -5 @vinnies said:

Dec 13, 2011 9:50:36 GMT -5 Sandbagger said:

Flickering how? A few segments or the whole display. Most often I see older radios with flickering segments, which turnes out to be a product of dirty channel selector switch contacts.

If I remember correctly, the display has its own regulator (actually a TO-220 case transistor) bolted to a heatsink, but if the problem isn't dirty contacts, a check of the display voltage is in order.

Seems mostly segments. If there any way to get at the internals with Deoxit?

Those are sealed switches. I usually just turn them 'round and 'round and back again a whole bunch of times and that seems to help for a little while. Heck even my relatively new Galaxy 2547 has some "twinking" segments and I have to wiggle the dial to correct.

[Deleted]

Ugh, the copper foil is pealing from the ribbon cable. I may have to mod it and convert it to hard wire.

Anyway, this apparently has a built in mic preamp. Should I use a dynamic mic with this, because a power mike may be too loud?

[Sandbagger]

Dec 15, 2011 18:03:26 GMT -5 @vinnies said:

Ugh, the copper foil is pealing from the ribbon cable. I may have to mod it and convert it to hard wire.

Anyway, this apparently has a built in mic preamp. Should I use a dynamic mic with this, because a power mike may be too loud?

Not necessarily. There is a pre-amp (with an AGC circuit), but an amplified mic works fine. It seems to sound really good with a Turner +3. You just don't need to turn it up as much as you would with an older radio with no internal mic amp.

[cbrown]

Dec 15, 2011 18:27:51 GMT -5 Sandbagger said:

Not necessarily. There is a pre-amp (with an AGC circuit), but an amplified mic works fine. It seems to sound really good with a Turner +3. You just don't need to turn it up as much as you would with an older radio with no internal mic amp.

What Sandbagger said. Just keep the drive level lower on the power microphone.