Motorola 555 ssb base tx issue

[Handy Andy]

Freeze spray - glad to know you have some...

That can help but if the "Heat" in the kitchen isn't the issue, but the Length of time it takes to recover it - I find interesting.

Ok, I mentioned heat because of what I saw here...

Foil Side



Top Component Side...

​

This shows to me, heat fatigue - the flux and preservative used on the board got hot right around whatever is by that regulator.

The Semiconductors are NOT they only ones affected by heat, caps are too (in fact all parts are interrelated) - I think it was mentioned earlier about Capacitor ratings; one being temperature - that may affect how they operate and they don't quickly recover like their Resistor or semiconductor cousins do

Also saw this...

This is a Classic "forgot to address - redress"​

In the way this radio is assembled, you may have more work to do to correct such lead dress oversights - I hope that when the radio was put together - lead dress like the above didn't pinch and further damage parts from the short that it would have caused.

 

[b2cooll]

Very good Info, "thanks" the pictures I showed were from a different rig.
I have been working on a base station, but opened up a mobile version to show some pictures, and that one has not been touched yet.

And yes I do so many places that could cause bad contacts, intermittent working and works one min but not the next. I look this over as I go thru this board in detail. And I will report my finding back here for all to read.

Bummer I was really hoping that ya-all would re-call the "Fix" on this as all 6 of my rigs do the same thing. When totally cold they will work perfect for 10 min, Good RX, good AM carrier and mod and good SSB @ 12 Watts, then the RF output will start to fade, kind of slowly to the point that only High modulation will get any RF out, AM or SSB ( 2 different paths ) until then there is no output at all. RX still good

I have replaced parts, re-flowed parts and looked for intermittent connections, pressing on board and what not to try to get the RF back if even for a second

Each time I am not able to get the RF to come back, even with some freeze spray.
The only thing that seems to get it to work again is having the rig turned off for 20-30 mins, then rinse and repeat.

So thanks ALL for the help, I will be out here more as I just retired from Fluke in Everett as I worked in their Primary Standards Laboratory for 35 years.

I also build some custom rigs, what I call Frankenstein CBs, feel free to check out my YouTube channel for some of my content,
73s Bruce in Seattle

 

[Retro CB Guy]

Sure is looking more and more like Motorola may not have designed these well in the TX section... I'm experiencing more of this now myself. After having my base recapped and aligned by Mike's Radio Repair some years back and had DDS installed, thinking it was gonna be an excellent combination hmmmm...

TX issue here is same notorious crazyness, shame on the mess!

I'm assuming Bruce didn't get to the bottom of this matter...

73's disappointed, Retro

 

[Radioman56]

If you'd like, contact me (Eric) @ Klein Communications about your Motoroa 555 "issue"., as I just might have that simple "C#xxx fix" for ya.!

Klein Communications | Buckhannon WV

Klein Communications, Buckhannon, West Virginia. 2,250 likes · 77 talking about this. Repair of Commercial FM 2-Way Radios, CB Radios & Amps - Design & Repair of Power Back-up Systems

www.facebook.com

or at

KY8E Callsign Page

KY8E personal biography

www.qrz.com

 

[Retro CB Guy]

If you'd like, contact me (Eric) @ Klein Communications about your Motoroa 555 "issue"., as I just might have that simple "C#xxx fix" for ya.!

Klein Communications | Buckhannon WV

Klein Communications, Buckhannon, West Virginia. 2,250 likes · 77 talking about this. Repair of Commercial FM 2-Way Radios, CB Radios & Amps - Design & Repair of Power Back-up Systems

www.facebook.com

or at

KY8E Callsign Page

KY8E personal biography

www.qrz.com

Yeah thanks, I'll be in touch soon!

73's, Retro

 

[AudioShockwav]

If you'd like, contact me (Eric) @ Klein Communications about your Motoroa 555 "issue"., as I just might have that simple "C#xxx fix" for ya.!

Klein Communications | Buckhannon WV

Klein Communications, Buckhannon, West Virginia. 2,250 likes · 77 talking about this. Repair of Commercial FM 2-Way Radios, CB Radios & Amps - Design & Repair of Power Back-up Systems

www.facebook.com

or at

KY8E Callsign Page

KY8E personal biography

www.qrz.com

It would be beneficial to others if you would share the way to fix the issue as it seems it may be a common problem.

73
Jeff

 

[208bonez]

Nice reply,
"Thank you" and did I hear the word DUT :^) a common term used in my calibration background.
Really this is a very detailed and thought out observation with some good suspects to look over.

I will go thru this CB and measure, measure and measure some more to tackle this issue until I find a solution to this.
Having several units that show the same symptom had me thinking this has to be a well known fault and this form would lead me right to it :^)
I understand, not an easy ask just not many Motorola CB experts.

I will not forget to post the results back to this thread as I will not stop my quest.

PS I also thought that the heat had to be the culprit,
But if true I would have thought the can of cold spray would have shown a faster recovery or a temporary OK condition as I got things Frosty

All my tricks up my sleeve could not get the RF to go active until the power was removed for 20min or longer. Room temp 75 degrees

Anyone Else ? that can dust off the old brain cells on this one.......
73s

The AM Pass regulator transistor is too small for stock. We replaced them under factory warranty. Use a Tip3055 to replace!

 

[208bonez]

Change the AM power regulator. It’s too weak stock and failed under warranty many times. I replaced many out of warranty with a good TIP3055 and small heatsink or an equivalent. Ssb Bias should be fine. I Check this with no modulation and on (lsb or usb) SSB mode in transmit. Use a multi meter on about the lowest DC voltage (less than a few) you can set it on. Ground the black lead to the ground or the chassis of the base. Then use the red lead on the base of the final output transistor. The middle pin (collector) should have 12v or supply voltage when keyed. The one to the side of it, one will (emitter) measure low to ground. The other pin should have about .6-.8 volts of bias on the (base) pin. When keyed up only! And, If this is here the bias is working. The base is the pin the bias voltage is on. Older bipolar transistors use about .6-.7 volts of forward bias to turn on the junction.
You can use a current meter here to be accurate. But to just get a reference voltage to see if where in the ballpark is fine! If you haven’t anything close to this voltage .6-.7v dc on transmit mode on ssb? If not then stop immediately and check the transistor and circuit. If you have it, then move on to the regulator.

The finals and bias should work too if there’s output on SSB when you modulate. This will work when the regulator has failed too. Common problem in these SSB rigs! The AM power regulator. Also, if you’re liking that big dead key on AM? Use a heatsink on a 2n3055 or 2n3772 for reg. and a 2sc1969 or 2sc2312 or 2sc1307 for final… if you can find one! I prefer the original 2SC1817 or the 2SC1307 or 1969

The mosfet finals will work here. The bias is a little trickier than most. It runs on a higher voltage and needs to come from a switched regulated source! It can be worked around, and stability on par with most other rigs in its class. A bit less heat too. I used IRF520’s with success. I prefer the original transistors besides the upgraded am power pass regulator.

Also important, the AM carrier be set at 3.8 watts. This is factory settings. The modulation when set correctly about 90-95% should be about 16 watts peak. Or about 6 watts rms.
SSB -10-12w pep
With stock final and tune.

Jerry S.
W8RBJ
208bonez