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I could sure use it also.?
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On Jun 11, 2022, at 12:09 PM, Gerard <kabupos@...> wrote:
? Evan,
?
You¡¯ve done a fantastic job with these oscilloscope screen copies.
But would it be even more interesting to actually have a scope screen of all the test points?? (20 i think)
It¡¯s a little more work, but it¡¯s worth it for troubleshooting and homebrewing.
Why not also integrate some screenviews of the hot spots (Ex Q90, mixer,...)
cdt
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On Sat, Jun 11, 2022, at 11:14 AM, Gerard wrote:
Evan,
I forgot, specify the bandwidth and model of your oscilloscope, the measurements can be different depending of our oscillo.
Thank's
I use a Siglent SDS 1102CML+ 100MHz scope. I have posted some of the other test points in prior emails.? The ones recently are for testing the transmitter.? I have not looked at the IF stages but have measured the clock signals (TP12, 15, and 18). I will post some of the other test points if I can find the time.? Right now, I am working on our build club process and presentation. 73 Evan AC9TU
?
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I should add that the information posted gets lost on the Groups.io site.? Even when put in the "files" or WiKi sections, no one seems to be able to locate the information.? Most of my replies are reposting of prior info shared.
I have started to keep track of solutions on both the web and file sections on my computer.? When a problem arises, I try to post the information I saved.? If there is a better way, then I do not know it.? This group is treated as a help desk, so it is up to the helpers to have the information available.? The average poster will not know all the locations to find solutions.
The above are my thoughts.? Others can have differing opinions, and that is OK.
73
Evan
AC9TU
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Evan + Others ¡ª your help desk like support enables MANY of us to accomplish what, on our own, we could never do. ?
Evan¡¯s observations ¡®bout where to find help on a specific topic/issue are spot on. Searching the wiki, files area, posts, HF signals, FB, redit, ?the global web, etc etc are all hazardous and uncertain.?
in a way, you most helpful folks are like modern day wizards of the cosmic library. You have the technical scope and institutional memory to point us to the published remedial text.?
Why does it work this way? Most all newbies stumble at familiar points. ?The uBITX is well established and understood. ?But to us neophytes, every pot hole, self inflicted wound, error, boo-boo, is 100% new and unexpected and novel. ?But also well worn and predicable ?to the ¡°help desk staff¡±.?
I¡¯m only one of hundreds (more?) who are successfully because of your kindly ¡°help desk¡± like ?support.
So thank you!!
Don
km4udx
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Don, you are spot on! The guys providing common sense support are excellent. And I can¡¯t say enough about the time and effort that Evan puts in. It has to be a true labor of love!
Thanks to all!
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On Jun 12, 2022, at 10:44 AM, Don - KM4UDX <dontAy155@...> wrote:
? Evan + Others ¡ª your help desk like support enables MANY of us to accomplish what, on our own, we could never do. ?
Evan¡¯s observations ¡®bout where to find help on a specific topic/issue are spot on. Searching the wiki, files area, posts, HF signals, FB, redit, ?the global web, etc etc are all hazardous and uncertain.?
in a way, you most helpful folks are like modern day wizards of the cosmic library. You have the technical scope and institutional memory to point us to the published remedial text.?
Why does it work this way? Most all newbies stumble at familiar points. ?The uBITX is well established and understood. ?But to us neophytes, every pot hole, self inflicted wound, error, boo-boo, is 100% new and unexpected and novel. ?But also well worn and predicable ?to the ¡°help desk staff¡±.?
I¡¯m only one of hundreds (more?) who are successfully because of your kindly ¡°help desk¡± like ?support.
So thank you!!
Don
km4udx
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Getting closer to the solution. Here's what I found probing around: RF probe readings today (they fluctuate a bit from day to day)
TP3: 384
Q911 base: 362 Note that when I attach the probe here I actually see output power on the wattmeter (?)
Q911 Collector: 31 (!!)
T9 pin 4: 30
T9 pin 3: 20
T9 pin 2: 7
T9 pin 6: 6
T9 pin 1: 3
So it looks like either or both Q911 and Q912 are bad? I am out of similar 2N3904 or 2N2222A and have some coming this week, so I'll look at replacing them. Interesting that the bias voltages look fine, but clearly they are not amplifying.
I may have to make up a permanent RF probe! This one is cobbled on a small piece of perf board with clip leads to probe leads, but it is proving most helpful.
=Vic=
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Vic,
One of the two transistors could have an open B/E link, with resistance on the collector to emitter.? The voltage measurements could be measuring the good transistor.? The output could be reduced due to the second one not functioning.? Maybe you can check them when you pull to replace them.? I use this device to check 3 terminal active devices.
73
Evan
AC9TU
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Vic,
After you get your replacement parts, ohm out the solder pads to make sure there isnt any delaminated pads your dealing with. microscopic cracks in the traces and such.,Also check for any open traces. I used to repair stuff back in the day and lighting and heavy static charges might open up a trace or two.
also just a back yard technician trick, you could inject an rf signal from a signal generator or oscillator into the pre driver section to see if the signal will push to the finals. you can use a scope or rf probe to trace this on the driver transistors and the inputs of the finals. just like tracing out an audio problem .? you can either work from the finals and work backwards lowering the signal generator level on each stage attenuating the signal level, or go to the pre driver stage and increase level as you work forward towards the finals.Scope or rf probe will definitvely show where you lose it.
just my gorilla way of troubleshooting.
73
David
ac9xh
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I agree with Evan,
in circuit paths can simulate a good voltage until you actually pull it out and test it,unless you have a transistor tester that does it in circuit,.
replace them and check voltages, .also if you have a signal generator, inject an rf signal thru the circuit and scope it out.
73
David
ac9xh
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Vic,
forgot to say,
before you replace the transistors, check the biasing resistors going to each transistor in that circuit. with the transistors out it will give a better isolation to check each resistor better. You can then ohm out the traces just in case you have an open from the solder pad to trace,etc.
also check coupling capacitor if everything seems normal after getting parts. this is the coupling capacitor c84? i believe. Im reading off the v6 schematic.
Also the 2.2 ohm resistor r89 could cause the problem of no output except when you touch a component.? I believe Raj mentioned this on one of his posts.
also check your transmit and receive relay circuitry.Your tx line comes from that and also to r89. Someone stated your voltages are down earlier? check your voltages on the k1 relay since it feeds r89 with 12 volts i believe. if your voltages there look good going to q911 and 912,replace them and see if normal operations resume. Ive seen components read good until under load . they look good and measure good until a voltage is applied and then they start breaking down under load. Did you state you replaced them before? Maybe a bad connection from pad to trace or from that circuit to transformer also.
Just throwing out some head scratching for you.
hope this helps and hope i didnt sound too stupid
73
david
ac9xh
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To me it means the power amp from Q911 is working as it is oscillating and output producing power.
Concentrate on Q90 area. best way is use a sig gen to drive the amp and check.
Raj
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On 13/06/2022 10:49 PM, Vic WA4THR via groups.io wrote: Getting closer to the solution. Here's what I found probing around: RF probe readings today (they fluctuate a bit from day to day)
TP3: 384
Q911 base: 362 Note that when I attach the probe here I actually see output power on the wattmeter (?)
Q911 Collector: 31 (!!)
T9 pin 4: 30
T9 pin 3: 20
T9 pin 2: 7
T9 pin 6: 6
T9 pin 1: 3
So it looks like either or both Q911 and Q912 are bad? I am out of similar 2N3904 or 2N2222A and have some coming this week, so I'll look at replacing them. Interesting that the bias voltages look fine, but clearly they are not amplifying.
I may have to make up a permanent RF probe! This one is cobbled on a small piece of perf board with clip leads to probe leads, but it is proving most helpful.
=Vic=
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Evan, I picked up a device at the 2019 Hamvention that looks identical to that one except for the color of the case. It has been amazingly useful with transistors, capacitors, etc.,and how I found that Q90 (2N3904) was bad when I pulled it. After mis-installing the replacement 2M2222A, I tested it before reinstalling it to make sure it was OK on my tester and it was good.
I live on a small farm and this time of year it is tough getting much time to work on this stuff as I spend a lot out in the fields. January and February are usually when I get to play on the bench, so sometimes it takes a day or 2 before I can try something else, but I want to get this working as I have a lot of fun with it on a battery at the beach when we vacation there toward the end of summer.
=Vic=
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Thanks, Raj. I do get a good signal from TO3 right up to the base of Q911, but not after that transistor, which is why I am looking there, but the power indication (only about a watt) when I probe that section is puzzling, for sure. However, I am using an unshielded set of leads and RF probe circuit, so it may be radiating enough signal to partially be picked up by following stages, perhaps.
And roger on low supply voltages, a known situation. When I built his I was concerned about use from a relatively unregulated power source (actually a car) where the voltage can approach 15v, and also the opportunity to run higher voltages to get more power without damaging the circuits. So I made a 12v regulator circuit that feeds everything except the PA transistors. The source I am using in the shack is 13.4v, but that isn't enough to regulate, and more use is in the field where I am using a 12v Lithium pack, so even worse, so internal voltages of 10-11v are common. I have found the rig operates well until the internal voltage gets down to around 9v, but since I never use it on the original higher voltage I plan to remove that regulator since it isn't helping anything. Just haven gotten around to that since it is packed into the corner where the power comes in.
=Vic=
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Thanks, David. I disposed of all my ancient tube-type scopes, VTVM, and RF probe a long time ago and I don't have anything but a couple DVMs and RF wattmeters for most test work. I never had a signal generator. I did cobble up an RF probe for this situation, and when all is done I may make a more permanent, shielded version. I only do repairs when I have to on my own stuff, and it is never something I look forward to doing. Sort of like welding stuff or repairing tractors here on the farm...not because I want to but because there isn't another option out in the middle of nowhere.
=Vic=
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Farmer here also Vic, I grow coffee. Monsoons have started and everything is very wet for the next few months.
The probe at 911/2 is acting like an antenna and the whole circuit is oscillating. This should also happen at Q90.
I would take the next guess as T8. Try rocking the toroid side ways, sometimes this fixes the shorts.
Raj
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On 14/06/2022 2:37 PM, Vic WA4THR via groups.io wrote: Evan, I picked up a device at the 2019 Hamvention that looks identical to that one except for the color of the case. It has been amazingly useful with transistors, capacitors, etc.,and how I found that Q90 (2N3904) was bad when I pulled it. After mis-installing the replacement 2M2222A, I tested it before reinstalling it to make sure it was OK on my tester and it was good.
I live on a small farm and this time of year it is tough getting much time to work on this stuff as I spend a lot out in the fields. January and February are usually when I get to play on the bench, so sometimes it takes a day or 2 before I can try something else, but I want to get this working as I have a lot of fun with it on a battery at the beach when we vacation there toward the end of summer.
=Vic=
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I repaired a radio with what looked like 911 and 912 bad. Both of the emitter resistors were cracked. Transistors were fine
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73
Dave
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Vic,
Here is an inexpensive shielded RF probe kit.? I have built and tested it, and it works well.
A fellow builder and I are doing a club presentation on modern test equipment for today's Ham.? From our analysis, IF you had to pick one instrument for troubleshooting, it would be a digital oscilloscope.? They range in price from about $80 for a 20MHz USB version to over $10,000.? The sweet spot for economical-minded Hams with occasional use would be a $170 Kiprim that does all that a DMM does except current measurements.? It also does signal purity measurements(spectrum analysis) that would be good enough for most uses.?
If you are willing to spend a little more, then our recommendation is:
We have tested all of the above.? The difference in the Oscopes is the accuracy of the voltage readings.? If three digits are good enough for you, then the Kiprim is OK.
DISCLAIMER - The above are measurements done on a single device purchased from the manufacturer and represent our experience with that single device.? It is not a guarantee that you will have the same experience.? We have no connection to any of the instruments except as a customer.
On a personal note, I use Amazon because of the return policy.? If something does not meet my expectations, I can return it within a reasonable time.? You can find better prices from other sources.
73
Evan
AC9TU
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/g/BITX20/message/76735
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73
Dave
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On Tue, Jun 14, 2022 at 10:19 AM, _Dave_ AD0B wrote:
/g/BITX20/message/76735
Dave, Did you verify that the trace between the two power connections under the header was cut?? If not, then the higher voltage would be sent to the mainboard and that could damage multiple components on it. It would be an improvement in the v6 design if the board trace was replaced with a jumper that would allow separate power fed to only the finals. That would also allow for testing the transmitter sections without running the finals. 73 Evan AC9TU
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I don't want to get too off topic Evan???but yeah the power wires that he used were the wrong color code. Ground red, Black was the +12 and yellow were the finals.?
Had forgotten about those arrows at power inlet Toward the center of the pic were two tiny arrows which highlighted the main issue.
The unit was bought used and modified into not working by the original owner and was described as working good. When it didn't work Steve was lost. I basically returned most of the wiring to stock.
I posted this as the same circuit seems to be involved and could be checked easily with a VOM.
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73
Dave
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Vic WA4THR
Raj vu2zap
_Dave_ AD0B