I was gonna buy a LG-1311 (used) after watching your video on I.F. filter sweep. Now you convinced me, I do not have enough knowledge to buy vintage gear that can have fault anytime without a godd reason!
New subscriber here. Working my way through your videos from the beginning, watching the ones that seem interesting to me. You can expect some comments on older videos to appear regularly for the next week or so. Nice tracking job. It reminds me of a story my father told. He was a radarman on the USS Newcomb (DD-586) and was trying to track down a difficult problem. He studied the schematic time after time until he thought he understood the function of every component except one resistor, which seemed to connect two completely different parts of the circuit. He eventually solved the problem (it wasn't the resistor) but filed this mystery resistor away in his head as something to think about later. Much later, he had an opportunity to speak with a factory technician while the Newcomb was at a shore base. He asked about the resistor and was told, "Oh; that is a 'working resistor'." He had never heard of such a thing, and the technician said, "Well, if it isn't there, the radar doesn't work." It seems as though that was an "un-working" capacitor. With it, the signal generator doesn't work (or at least not properly). I just bought a cheap function generator kit. When I have it finished, I will have to examine the output carefully to be sure there are no spurious signals riding on the desired output. I've been an electronics hobbyist since the late 1940s (I was five years old) when my father made me a short-proof 10 VDC power supply (B+ transformer hooked up backwards with a selenium rectifier) and gave me a pile of switches, lamps, and buzzers (all screw terminals) with a good supply of salvaged (varnished cloth insulation) #18 solid hookup wire.
Excellent video! I have an LG1311 that I got from a club sale. It turned out to have the same symptom as yours, and omitting the capacitor cleared it up! Good find! With that repaired, I undertook the task of aligning the LG1311 per the calibration procedure (looks to be the same documentation you show in your video). It was going well, but I ran into a problem... At step 8, the forth bullet point item states"Check that the frequency with the Dial at 1 is one tenth the frequency measured with the DIal at 10." When I did this, I got a frequency of ~200Hz instead of the 100Hz I was expecting. Repeating step 8 didn't seem to help. I tried the other Ranges, and the result was the same; the measured frequency at 1 on the DIal was ~ .2 x the frequency at 10. I rechecked the voltages and supply lines for DC and AC, no apparent problems. All the unit functionality I've checked seems to be working as well. The Frequency pot on the front panel is 1k (taper unknown), and appears to be original. It has no wear issues so far as I can tell. My question is: do you see this problem on your 1311? If so, is this normal operation? It's not critical for my usage (I can always hook a frequency counter to the Sync output), but it seems a little sloppy for a piece of test gear. Any suggestions would be appreciated. Thanks!
I just discovered your videos today. I have to tell you that I really appreciate that you take the time to do these. Most of what I see just says "I replaced the coil" without any explanation of how that conclusion was arrived at except maybe, "I knew through past experience". Your amazingly cogent explanations are very helpful. I'm not a novice, but I get stuck more often than I like and your videos are extremely helpful. Again, thank you so much.
Awesome video! I've been an EE for a long time and still have much to learn. And yes, the supply is stable ... with a stable load. Looking at the supply with a pulsed or reactive load might reveal that some form of compensation is necessary after all. I suspect the cap fully bypassing the feedback divider is too aggressive, and a resistor in series with it might do the trick.
If you get the chance, and have the inclination, please post more repair videos. They are very lacking, both here on You Tube, and in general. Real world, real time examples of problem finding are far better, not to say far more interesting, than reading theory. Nice video, cheap fix ;) Thanks, you have created a unique and enjoyable set of films
Nice troubleshooting and video, it is fun to follow along, kind of felt like I was right in there doing it myself but I always learn something new from you...keep it up with the videos, very educational.
Yes, that all makes sense. I have been a bit ESR crazy since I built my ESR meter a few months ago, but you are right, in this application, any reasonable value would not have an effect certainly not 1 or 2 ohms. Now I am probably going to have to try and track one of these regulators down and experiment with it to see if I can replicate the problem, :) . From looking around on the web they seem to have a good reputation with audio guys, so the overall design must be good.
This capacitor raises the HF gain in the FB loop. The phase response of the loop lags more and more with rising frequency. If the gain of he loop has not fallen enough (gain is < 1) by the time the phase changes by 180 degrees the loop will oscillate. This is typical of FB loops. You just need to lower the value of this capacitor and the loop will stabilize. Have never seen this capacitor in good design. Better a poly/ceramic. Electrolytics are often +80 -20 percent.
I pulled up the datasheet for the M5230L and noticed in all the circuit examples the values of Cref was 1uf, from what I could tell the function generator used 10uf. The dielectric material used for the capacitor was not specified in the datasheet. I wonder if the preferred material would have been say 1uf Tantalum? It would be interesting if maybe you would try a Tantalum of about 1uf or maybe even a monolithic ceramic of about .5 uf or so to see what the response would be. (Continued)......
You may want to correspond with Dave Jones (EEVBlog). His videos are awesome and very well made. For a start you may want to invest in some good tripod. Great video and very educational. Also nice clear passionate voice with the right intonation.
Another fascinating piece of work, I was just wondering about ageing (don't we all !) would the pass transistor be a suspect for drifting about ? do you remember the part ? 2N3055 maybe ? and I bet that regulator is a pig to find, anyhow great video...cheers.
Thanks for this. I have a Leader LG-1300 with the same kind of problem. However, it uses a different design with +/- 10 VDC adjustable, and +/- 15VDC non-adjustable. The 10V is dead voltage-wise but there is mucho crude on the scope at the 10V test point. Still at the head scratching stage. de K8nn
Do you think if you measured the capacitance under dc bias, you would see a bad value? Presumably the thing worked... Nice tip about the false triggering...next time i have trouble with the MSO scope and blaming tektronix I will look for something riding on the waveform.
Would you mind sending me the schematics for the LG-1311? I have one, it suddenly quit working, 17v check points are down to 4.32v both negative and positive. I'm thinking it might be the R114-115 resistor's, both are reading 50 ohms but I don't know what they are. Schematic would be very helpful. Keith
Even though the cap checked good, I would be curious to know what the ESR of the cap was. Did you check the caps equivalent series resistance. Just curious.. Nice video as always.
(Continued from below) Regardless, this has me curious enough that I am going to put in a watch on ebay for this same function generator and see if I can get one and compare it to what you have observed. If it has a similar problem, maybe it was a design mistake from long ago. Maybe the Aluminum electrolytics get leaky and mess up the timing of the feedback?? Or High ESR is a problem? Regardless, I had been keeping an eye out for a decent one anyhow since I don't have a good quality one to use.
I like this video but wouldn't call this a repair. Obviously, something else malfunctioned, perhaps the expensive or unobtainum IC. The thing worked correctly from the factory and then stopped working correctly, which begs the question, why?
I encountered a similar issue that you had with your FG. Mine happened with a CCD camera. I posted a video of this and referenced your experience as well. (youtu.be)/Z_IfCNX3OlU
I was gonna buy a LG-1311 (used) after watching your video on I.F. filter sweep. Now you convinced me, I do not have enough knowledge to buy vintage gear that can have fault anytime without a godd reason!
This generator is certainly still usable even with this subtle fault.
New subscriber here. Working my way through your videos from the beginning, watching the ones that seem interesting to me. You can expect some comments on older videos to appear regularly for the next week or so.
Nice tracking job. It reminds me of a story my father told. He was a radarman on the USS Newcomb (DD-586) and was trying to track down a difficult problem. He studied the schematic time after time until he thought he understood the function of every component except one resistor, which seemed to connect two completely different parts of the circuit. He eventually solved the problem (it wasn't the resistor) but filed this mystery resistor away in his head as something to think about later.
Much later, he had an opportunity to speak with a factory technician while the Newcomb was at a shore base. He asked about the resistor and was told, "Oh; that is a 'working resistor'." He had never heard of such a thing, and the technician said, "Well, if it isn't there, the radar doesn't work."
It seems as though that was an "un-working" capacitor. With it, the signal generator doesn't work (or at least not properly).
I just bought a cheap function generator kit. When I have it finished, I will have to examine the output carefully to be sure there are no spurious signals riding on the desired output.
I've been an electronics hobbyist since the late 1940s (I was five years old) when my father made me a short-proof 10 VDC power supply (B+ transformer hooked up backwards with a selenium rectifier) and gave me a pile of switches, lamps, and buzzers (all screw terminals) with a good supply of salvaged (varnished cloth insulation) #18 solid hookup wire.
Excellent video! I have an LG1311 that I got from a club sale. It turned out to have the same symptom as yours, and omitting the capacitor cleared it up! Good find!
With that repaired, I undertook the task of aligning the LG1311 per the calibration procedure (looks to be the same documentation you show in your video). It was going well, but I ran into a problem...
At step 8, the forth bullet point item states"Check that the frequency with the Dial at 1 is one tenth the frequency measured with the DIal at 10." When I did this, I got a frequency of ~200Hz instead of the 100Hz I was expecting. Repeating step 8 didn't seem to help. I tried the other Ranges, and the result was the same; the measured frequency at 1 on the DIal was ~ .2 x the frequency at 10.
I rechecked the voltages and supply lines for DC and AC, no apparent problems. All the unit functionality I've checked seems to be working as well. The Frequency pot on the front panel is 1k (taper unknown), and appears to be original. It has no wear issues so far as I can tell.
My question is: do you see this problem on your 1311? If so, is this normal operation? It's not critical for my usage (I can always hook a frequency counter to the Sync output), but it seems a little sloppy for a piece of test gear.
Any suggestions would be appreciated. Thanks!
I just discovered your videos today. I have to tell you that I really appreciate that you take the time to do these. Most of what I see just says "I replaced the coil" without any explanation of how that conclusion was arrived at except maybe, "I knew through past experience". Your amazingly cogent explanations are very helpful. I'm not a novice, but I get stuck more often than I like and your videos are extremely helpful. Again, thank you so much.
Excellent job, textbook example of good fault finding.
73, Eric
Just an excellent instructive video. I like to trouble shoot faulty electrical circuits, so this video was very enjoyable.
Awesome video! I've been an EE for a long time and still have much to learn.
And yes, the supply is stable ... with a stable load. Looking at the supply with a pulsed or reactive load might reveal that some form of compensation is necessary after all. I suspect the cap fully bypassing the feedback divider is too aggressive, and a resistor in series with it might do the trick.
If you get the chance, and have the inclination, please post more repair videos. They are very lacking, both here on You Tube, and in general. Real world, real time examples of problem finding are far better, not to say far more interesting, than reading theory. Nice video, cheap fix ;) Thanks, you have created a unique and enjoyable set of films
Nice troubleshooting and video, it is fun to follow along, kind of felt like I was right in there doing it myself but I always learn something new from you...keep it up with the videos, very educational.
Really great troubleshooting! Stability in feedback loops is fascinating stuff. Keep up the good work.
Yes, that all makes sense. I have been a bit ESR crazy since I built my ESR meter a few months ago, but you are right, in this application, any reasonable value would not have an effect certainly not 1 or 2 ohms. Now I am probably going to have to try and track one of these regulators down and experiment with it to see if I can replicate the problem, :) . From looking around on the web they seem to have a good reputation with audio guys, so the overall design must be good.
Wow the resolution of this post has not degraded over 7 years.
Theory and Trouble shooting of Electronics,,,My favorite topics,,,,,Keep up the Good Work,,And Videos!!!
This capacitor raises the HF gain in the FB loop. The phase response of the loop lags more and more with rising frequency. If the gain of he loop has not fallen enough (gain is < 1) by the time the phase changes by 180 degrees the loop will oscillate. This is typical of FB loops. You just need to lower the value of this capacitor and the loop will stabilize. Have never seen this capacitor in good design. Better a poly/ceramic. Electrolytics are often +80 -20 percent.
You have learned electronics very well, sir!
I pulled up the datasheet for the M5230L and noticed in all the circuit examples the values of Cref was 1uf, from what I could tell the function generator used 10uf. The dielectric material used for the capacitor was not specified in the datasheet. I wonder if the preferred material would have been say 1uf Tantalum? It would be interesting if maybe you would try a Tantalum of about 1uf or maybe even a monolithic ceramic of about .5 uf or so to see what the response would be. (Continued)......
You may want to correspond with Dave Jones (EEVBlog). His videos are awesome and very well made. For a start you may want to invest in some good tripod.
Great video and very educational. Also nice clear passionate voice with the right intonation.
Another fascinating piece of work, I was just wondering about ageing (don't we all !) would the pass transistor be a suspect for drifting about ? do you remember the part ? 2N3055 maybe ? and I bet that regulator is a pig to find, anyhow great video...cheers.
Thanks for this. I have a Leader LG-1300 with the same kind of problem. However, it uses a different design with +/- 10 VDC adjustable, and +/- 15VDC non-adjustable. The 10V is dead voltage-wise but there is mucho crude on the scope at the 10V test point. Still at the head scratching stage. de K8nn
really nice troubleshoot I like this!!! Hope seeing more videos like this! 73s
This is amazing tutorial! Thank you very much!
Do you think if you measured the capacitance under dc bias, you would see a bad value? Presumably the thing worked... Nice tip about the false triggering...next time i have trouble with the MSO scope and blaming tektronix I will look for something riding on the waveform.
Good video and very good repair story. Thanks for sharing.
Would you mind sending me the schematics for the LG-1311? I have one, it suddenly quit working, 17v check points are down to 4.32v both negative and positive. I'm thinking it might be the R114-115 resistor's, both are reading 50 ohms but I don't know what they are. Schematic would be very helpful.
Keith
Even though the cap checked good, I would be curious to know what the ESR of the cap was. Did you check the caps equivalent series resistance. Just curious.. Nice video as always.
Did that cap have any high esr Alan, maybe it was on the verge of a small reistance. Thanks for sharing.
(Continued from below)
Regardless, this has me curious enough that I am going to put in a watch on ebay for this same function generator and see if I can get one and compare it to what you have observed. If it has a similar problem, maybe it was a design mistake from long ago. Maybe the Aluminum electrolytics get leaky and mess up the timing of the feedback?? Or High ESR is a problem?
Regardless, I had been keeping an eye out for a decent one anyhow since I don't have a good quality one to use.
Very good video as always
I like this video but wouldn't call this a repair. Obviously, something else malfunctioned, perhaps the expensive or unobtainum IC. The thing worked correctly from the factory and then stopped working correctly, which begs the question, why?
Hi,
I have that kind of a prob;em with a VICTOR VC2002 .
nice video
Good Video.
I encountered a similar issue that you had with your FG. Mine happened with a CCD camera. I posted a video of this and referenced your experience as well.
(youtu.be)/Z_IfCNX3OlU