Hand wired d201 burning up R4 (47k 2w) and R5 (100 ohm 7w)

[aardvark]

So yesterday I had my d201 on just listening to local chatter and all of a sudden the receive audio dies and has just a slight hum. Then I smelled the magic smoke.  I open the bottom and discovered that R5 was burned and had broken in half. So today I went to  Newark and picked up a few 100 ohm 10 watts. Came home and started changing r5 and found r4 also broken in half. Thinking this is because of their age I didn't think much else about it. I replaced both resistors. Plug the radio back in and turned it on and immediately was greeted with more magic smoke, checking I found r5 very hot and could tell r4 had been hot also. So now to the question. Has anyone else experienced this? It is obviously a very high current draw problem (short maybe?) this appears to be related to recieve. Hope it might be a tube verses the Mod transformer. Any ideas or help appreciated. 

[2600]

Odds are you'll find that the tall 3-section 40uf 450V has a shorted section.

If it's the factory-original part, the miracle is that it lasted this long. A peek under the chassis usually reveals signs of leakage from inside, sometimes in the form of dusty-brown stuff that is left when the leakage dries up.

That kind of component is intended to last for ten or fifteen years, under regular use.

Frequently they last longer. But a radio that's 40-plus years old is way past borrowed time.

I don't know the total number of electrolytic caps in the radio, but it's a lot.

If you want to make the radio reliable, every single one of them must be replaced, whether it checks bad today or not.

Or you could play what we call "electronic Whack-A-Mole". Troubleshooting the bad part as they break down one or three at a time and replacing only the part that causes trouble today.

If you hear the old-radio guys use the term "re-cap the radio", this is what they mean.

This is not a trivial chore, but there it is.

73

[aardvark]

Thanks 2600. This radio was recapped and resistors replaced about 4 years ago. But it looks like the old multi-caps are still there. So I will check them. Don't know why they were not changed then. I looked and didn't see any evidence of failure visually, but that doesn't mean a lot.  I will check them today and report back.

[aardvark]

Mr 2600 as I continued checking today I found r649 (100k 1w) and c626 ( .01 disc cap) destroyed/burned. These are in series off the plate tab of v603 6l6gc audio tube and marked as the anti-vox line. I checked the 3 section cap and all sections show around 8m to ground after the charging of the section, no shorts or low resistance to ground. Looks like something in the anti-vox line maybe. What is your opinion? or any ideas/ past experiences?

[aardvark]

Mr 2600 As the saga continues, I have found there was a mod. in the area of the failures that looks like it may have been something to do with modulation. D602 was paralleled with a 330k resistor. This is the line coming from C626   and R649.  Modulation mod? or vox mod?  This is an old modification.  Any Ideas?

[aardvark]

And the saga continues!!  I replaced all the burned parts installed the new multi-section can caps and powered the radio up. Everything lights up and I can hear slight hum from the speaker. Checking further, I find that I do not have the 4 MHZ from j100a on the synthesizer board. I think maybe q100 is dead checking the voltages I have the 12vdc to it. Just no 4 MHZ out. So I have just have the 16MHZ from the j100b.  Thinking back on events. We had a huge snow storm Sunday and power lines went down all over the area. My power came back on Monday at 2:30pm. The tram died around 4 or 5 pm. Looks like it was a victim of a power surge that probably shorted c626 and started the whole chain of events. Does this sound reasonable?  So my next step is to restore the 4 mhz section to hopefully bring this thing back to freq.  Suggestions? Histories? Observations? Experiences? Helpful tips? Anyone?

[aardvark]

Ok I haven't had much luck on my post on this site. But let me try this. I need help with my hand wired. Heres what I have done so far.
replaced the burned resistors and disc cap.
Replaced the two main caps in the power supply .
Checked all the resistors and caps around the mod output tube. 
Checked mod transformer-its good
Checked all the voltages-good
Changed tubes several times
Checked resistors and caps at final tube and driver. replaced a few that were out of tolerance.
checked the audio chain with the scope- mod is good upto the final mod tube. The output from the mod tube doesn't look to good and is much less than the mod from the driver.
the Mic is good tested on another d201 I have.

heres what I have now.

receive works sounds a little weak and maybe a little distortion.
 
On transmit
carrier is 3-4 watts but to get this neutralizing cap is screwed down tight
shows reverse modulation on the meter when talking loudly into mic and not much movement at all.

now I am at a loss, Any suggestions or experiences from the past that anyone has had with this kind of problem?

[Sandbagger]

Jan 26, 2019 19:55:22 GMT -5 aardvark said:

Ok I haven't had much luck on my post on this site. But let me try this. I need help with my hand wired. Heres what I have done so far.
replaced the burned resistors and disc cap.
Replaced the two main caps in the power supply .
Checked all the resistors and caps around the mod output tube. 
Checked mod transformer-its good
Checked all the voltages-good
Changed tubes several times
Checked resistors and caps at final tube and driver. replaced a few that were out of tolerance.
checked the audio chain with the scope- mod is good upto the final mod tube. The output from the mod tube doesn't look to good and is much less than the mod from the driver.
the Mic is good tested on another d201 I have.

heres what I have now.

receive works sounds a little weak and maybe a little distortion.
 
On transmit
carrier is 3-4 watts but to get this neutralizing cap is screwed down tight
shows reverse modulation on the meter when talking loudly into mic and not much movement at all.

now I am at a loss, Any suggestions or experiences from the past that anyone has had with this kind of problem?

Based on what I found, the 100 ohm 7W is R6, and R4 is 47 Ohms. And there is another identical 47 ohm R3 in parallel with R4 which should also be "burning up". These are in the 410V supply line and if they are burning up then something in that circuit is pulling more current that it is supposed to. The 410V B+ voltage will be quite a bit lower with that much extra current drain. Usually I would look to leaky electrolytic caps first, but it looks like you've covered that. You also gave a clue with the audio power tube not doing what it should. Does the tube plate glow red (orange) when it's on? If C625 shorts, that would certainly shift the bias and cause the tube to draw more current and the plate would glow red.

To isolate the circuit that is drawing the extra current, may require temporarily disconnecting sections from the B+ voltage to see where the extra load is.

[2600]

It would appear he has gotten past the Chernobyl stage of troubleshooting. Says receive is weak?

Pin 6 on V400 may be fed by a half-Watt 47k resistor R402. Later production boosted it to a 1-Watt part. If V400 pin 6 shows much less than 100 Volts DC (with no receive signal) this would reduce sensitivity on AM alone, and would not affect SSB receive. The half-Watt part should get upgraded as an age issue, to a 1-Watt or 2-Watt resistor anyway. Just a guess, but worth a quick look.

Do you have a way to find out *how* weak you think the receiver is?

There are a few small electrolytic capacitors that can affect the receiver performance like C621, C625, . If any of them are original, that will become a problem if it isn't already.

The backwards swing suggest the drive level to the final tube could be weak. This tends to hurt the swing more than the carrier. The setting of the neutralizing trimmer cap C706 can also do this if it's not right. Always, always set the slug in the driver coil T700 for a peak with modulation, ESPECIALLY after disturbing the setting of C706. Any change to C706 will disrupt the peak setting of T700, requiring that you repeak it to get full drive into the final tube. Oh, and it also throws the Plate Tune on the rear panel slightly off of its peak, if you move C760 very much. Those three adjustments will interact in a big way.

We're getting close to some details that change from one version of the D201 to another. Which radio do you have? 23 channel or 40? Original version with the VOX control, or newer 23-channel radio with large circuit boards?

What looks like a single symptom like a weak receiver can easily be more than one problem, each one hurting performance only partway by itself.

The radio is too old to just assume that one problem has only one cause.

73

[321 treeclimber]

Im doomed. Its amazing to read what you guys do and know. I am not a tech or even a novice screwdriver jockey, as a matter of fact, faced with this kind of problem my radio would be nose down and sinking to the bottom of the kitchen trash can. Thank god for guys like you all. And aardvark i applaud your tenacious demeanor. Remember; "you must endeavor to persevere"! 321

[aardvark]

Tree Climber, Sandbagger and Mr. 2600 thank you all for the responses. Yes Mr. Tree Climber I am tenacious I don't like to quit or give up.  Mr. 2600 this tram is a d201 vox (handwired) as a matter of fact it has #28 stamped into the chassis so I am thinking it might be the 28th handwired built. Thats good info on the receive and I will check all of that. Also the info about the rf driver and t700 and the neutralizer may very well be my problem. I will be going back over that section with your suggestions in mind. Also let me ask. I replaced the two large multi-section caps in the power supply. the thing is, the one with the 10mf sections I replaced with one that has 3 x 20mf sections and 1 x 40mf section. And I am wondering if this may be causing a problem given where that are used in the circuits? Anyway thanks guys I was beginning to wonder if anyone even came to this site anymore.

More to come!!

 

[Sandbagger]

Jan 27, 2019 8:07:05 GMT -5 321 treeclimber said:

Im doomed. Its amazing to read what you guys do and know. I am not a tech or even a novice screwdriver jockey, as a matter of fact, faced with this kind of problem my radio would be nose down and sinking to the bottom of the kitchen trash can. Thank god for guys like you all. And aardvark i applaud your tenacious demeanor. Remember; "you must endeavor to persevere"! 321

Treeclimber, You probably won't want to take on a Tram D201 that has "issues". The D201 was probably Tram's best radio and had performance that could best just about every other CB radio made at the time. But the D201 does not age well. Due to it's design, the radio generates a lot of heat which can age parts and cause all sorts of nuisance issues, from relatively subtle to catastrophic. It takes a lot of probing and measuring to get to the root of most issues, along with a fairly good understanding of how that radio was designed. Guys who have worked on a lot of them start to notice the weak spots, and can reduce troubleshooting time by hitting those known areas first. But with any D201(a), all electrolytics should be replaced. All 1 and 2 watt carbon resistors should be replaced as well. Of course replace any weak tubes as well. I know that's kind of a shotgun approach, and I normally frown on that technique. But with a D201, it's necessary to bring the radio anywhere close to having a chance at performing as it did when it left the factory.

[aardvark]

Mr Treeclimber  don't worry about all of that. In this hobby you can take it as far as you want. If you want to talk then talk . If you want to work on your equipment and maybe learn a little something then do that. No right or wrong!! For me its right to work on my stuff, I love learning. I was a mechanical and electrical troubleshooter most of my life. I have been in radio since the early 70's. I am 65 years old today and I enjoy doing this stuff as it keeps my mind sharp hahaha I hope.

And Mr. Sandbagger, yes I got past the initial melt down and have the radio functioning, just not correctly yet. And as you point out those resistors are 47 ohm not 47k ohm. Sometimes these old fingers get ahead of the brain thats trying to control them. hahahaha

[321 treeclimber]

I really respect the insight aardvark. You got me by ten. I'm 55 feb.1 although i started cb early 70s as well. Ive come along way on my own repairs but that's on easy stuff like soldering and r&r. Not trouble shooting and diagnostics. Example got a lafy hb-111 with a elenco compressor amp attached and an old shure s36 with no end on it, my tube guy is done ge or the next month or longer...now what?

[aardvark]

Jan 27, 2019 16:38:01 GMT -5 321 treeclimber said:

I really respect the insight aardvark. You got me by ten. I'm 55 feb.1 although i started cb early 70s as well. Ive come along way on my own repairs but that's on easy stuff like soldering and r&r. Not trouble shooting and diagnostics. Example got a lafy hb-111 with a elenco compressor amp attached and an old shure s36 with no end on it, my tube guy is done ge or the next month or longer...now what?

research my friend  -the net- books-lots of good books out there- for ham radio but the concept is the same--ask questions-lots of questions

[321 treeclimber]

10-4 much respect, to you all. 321

[aardvark]

Mr. 2600-- update I set the RF circuit up and neutralized it according to the instructions which are the same in the tram manual and sams fotofacts. Then I tried tuning t700 while injecting a 1khz sign wave into the audio circuit. never got any forward modulation on output. Just reverse mod. got it keying about 4 watts and its backing up about a 1/4 watt. I used a generator to introduce a 1khz audio sign wave into the mic input. The signal coming out of V602 into the final audio tube is around 5 volts p-p with the mic gain about 20%. I attached a 0.1mf disc cap to the output side on the audio final and the output signal is about 1/5 watt p-p. and the same on the output side of the mod transformer. So still mod modulation. Really scratching my head about now.
 I can used a BK 2040 to generate a signal at channel 13 with a 1khz audio and test the receive and she is working good on receive with about 1mv RF and 50% mod from the BK 2040. and I can hear it very well even at that low level from the speaker. So that tells me the audio output circuit is working fine. and that part of the audio transformer is fine. Voltages are good on the audio tube. but something is killing the mod audio.  
Any other ideas?

[aardvark]

Just an update which I should have done much earlier. Turns out the modulation transformer was bad. It didn't test open(infinity) or shorted (0). it was just the last thing in the audio process I did not have confidence in so I replaced it. The modulation came to life. No the radio keys 4 and mods 8 watts. Feel good about this. While in the process I just refurnished the whole radio with new resistors and caps where needed.  Works excellent now. Thanks for every ones help.

[2600]

Wow! That is way cool.

Congratulations for sticking with it. That transformer is a truly-rare failure. Just shows nothing is fail-proof.

Gotta love it when a plan comes together.

73