Excalibur (3600 board) stuck...

[Hawkeye351]

Got a Colt Excalibur on the desk today. Nice looking radio, eat up with roach tracks and crap.

Cleaned it out thoroughly. Radio comes on but has very low volume on receive (signals are very good on meter though) even with volume wide open (barely hear it). Tried to transmit and it just makes a noise as though it keys, but it's not, still in receive. Noticed the On The Air light is constantly on as if it's stuck between transmit and receive.

Caps I replaced:
C195 and C194 (1000uf), C145 (330uf), C146 (47uf), C199 (330uf), C702 (100uf), C703 (100uf) and the big cap (3300uf) on power supply along with the 100uf small one beside it.

Got to be in the switching circuit somewhere.

Any thoughts guys/gals?

 

[TM86]

Putting this here so someone can tell me I'm wrong and hopefully post better info.

Looks like pin 3 on the mic is the RX/TX line. When it goes low it trips D81 and D82 to do their jobs. D82 runs off to TR33, D81 connects to IC4. IC4 is the NJM4558 dual op amp I've seen mentioned here multiple times, and not always in a positive light. I'd guess start around that.

Attached the schematic I found so others can play along at home. Hopefully they'll see something I missed and come up with the right answer.

 

[Cable Guy]

I'd look at ic4 4558, the tx switch/mic amp. Really concerned with voltages between the pins 5-8, that's the side that handles switching. I have seen them go bad.

 

[Hawkeye351]

Could be one of these original caps in front of the audio IC and near the mic/op amp. All these caps are original (30 to 45 years old), I only replaced the few that looked overheated and slightly bulging/opening, gonna replace all the caps in those two areas and then give an update on voltages for the mic/op amp.

If it's that mic/op amp then I have a whole sleeve of the JRC brand, I'll slap one of those in if the voltages are off with the new caps in that area.

 

[Klondike Mike]

... has very low volume on receive (signals are very good on meter though) even with volume wide open (barely hear it).

For this RX issue, if you hook up a speaker to the 3.5mm audio jack on the back, do you get the same results? What is the exact (EPT360010-15) main board # in that unit? There were many flavours of this radio using the same name.

 

[Cable Guy]

Yeah, what Mike said, and if the ext speaker Jack's internal speaker disconnect contact get corroded, the internal speaker either won't work or will be faint/scratchy. That wouldn't cause the always TX light. That's likely going to be a diode, capacitor or IC issue. The voltages at IC4 during RX/TX will tell you what to do about that.

 

[Hawkeye351]

Board number is "SRT-3600-10".

There is no difference between external speaker (3.5mm jack) and internal speaker volume. It does switch properly from internal to external speaker.

So far my 100uf caps I put in show as bad esr (new nichicons). Guess I got a bad batch of 100uf caps. That plus all the other original caps I haven't replaced yet is probably my whole problem.

The owner had just bought this radio from a tech down in SC. The owner ran it for a day and wasn't happy with the performance so he asked me if I would check it out for him, it did work then but performance was questionable. After getting the radio on my desk about 3 months ago I checked it out and noted all the issues I found. I then put it on the side so I could finish up the ones I was working on at the time. Well, I pulled it back out the other day and hooked it back up, then is when this issue popped up.

My guess,
The tech in SC needed money so he pulled this roach infested, dirty, filthy old radio out of the storage pile, fixed it just enough to sell it, the old original caps loosened up long enough to sell it and then I let it sit for 3 months after he ran it a couple days which dried up what little bit was left in the original old caps.

People around here have gotten to the point they bring me their old radios they've had in storage for years because they have sentimental value to certain radios. They want these old radios rebuilt. When they found out I rebuild radios, they started bringing me what some would consider junk and wouldn't touch, but I bring life back into them.

And thank you Mike for popping in. I thoroughly enjoyed your video series on the 142 rebuild and other videos. I've learned a lot from you and Kid-Vicious from copper forums. You gave me the confidence to recap these radios, I was always Leary of all those caps, lol.... Thank you for your contribution Mike.

Cable, thank you for your help on the other radio you recently helped me with. It's working great and the owner is tickled to have it back up to Par. It sounds amazing over the air.

I always tell my locals how great and informative this site is, the users are. Thank you guys.

I'll finish up today sometime and get back with you guys/gals.

 

[Cable Guy]

Check the power supply, Nomad points out an issue with it that is over volting the radio and trashing the audio IC.

Thread 'Oldest Galaxy base, kinda. Just doesn't say "Galaxy"'

Feb 22, 2024

This radio is as old as the Apple Macintosh. Date codes on the chips that have them are 1984.


No, it doesn't say "Galaxy" anywhere on it. But only inside it.

Sorta.

This circuit board number doesn't start with the letters "EPT", but it's the same format and the lowest "3600" followed by "10".

The older "Excalibur" radios were made by Cybernet in Japan. Not my favorite radio. Had stability issues.

This one says "Taiwan"...

• nomadradio
• Replies: 9
• Forum: CB and Export Equipment and Accessories

• 
• 

 

[DTB Radio]

Did you manage to fix this unit? There was one switching diode in the rx/tx switching circuit that seemed to fail at a fairly high rate in radios using that circuit. Unsure of its part # in your radio, but in the older Galaxy DX series (33HML, 44V, etc) it was D77, a KB362 part number. In a pinch, you can use a standard green or red LED as a replacement.

As for the low audio, besides the possibility of a bad audio IC, you may also have a bad support cap in the audio IC circuit. I'd look at the output of the audio chip on a 'scope to see if there's some kind of parasitic oscillation going on. Look at bypass and feedback caps if there is.

 

[Hawkeye351]

I had a family issue pop up. Plus my new order of caps should be in this week (had an entire batch of 100uf caps bad), switching brands of caps due to a bad batch of one value that I use a lot of.

D77 I think is correct. Thing is, this radio received and transmitted fine before and after I replaced only a few caps and realigned it, but then I put it up for months to get something else out of the way, recently I pulled it out again and this is the result of sitting a few months after being ran for a couple weeks after being pulled out of storage for God knows how long.

I'm inclined to believe other caps in the radio went out after I replaced a few and run it for a bit then stored it for a few more months longer. Plus my brand of caps are starting to show up as bad out of the bag. Gonna recap the radio completely with the new brand, even replacing the few I replaced previously.

Gotta keep the old tanks running, they may be old but they still have plenty of life in them if given a chance.

 

[TM86]

I had a family issue pop up. Plus my new order of caps should be in this week (had an entire batch of 100uf caps bad), switching brands of caps due to a bad batch of one value that I use a lot of.

D77 I think is correct. Thing is, this radio received and transmitted fine before and after I replaced only a few caps and realigned it, but then I put it up for months to get something else out of the way, recently I pulled it out again and this is the result of sitting a few months after being ran for a couple weeks after being pulled out of storage for God knows how long.

I'm inclined to believe other caps in the radio went out after I replaced a few and run it for a bit then stored it for a few more months longer. Plus my brand of caps are starting to show up as bad out of the bag. Gonna recap the radio completely with the new brand, even replacing the few I replaced previously.

Gotta keep the old tanks running, they may be old but they still have plenty of life in them if given a chance.

May I ask which brand of caps? I'd like to avoid them if I can.

 

[Hawkeye351]

Nichicon, only brand I been using for the past several years. But seems like high demand for Nichicons has resulted in less quality control.

 

[TM86]

Nichicon, only brand I been using for the past several years. But seems like high demand for Nichicons has resulted in less quality control.

That's... disappointing.

 

[Hawkeye351]

Maybe just an employee error, first time I ever ran across any bad ones from nich.