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Hello All, Yup still trying to get my sBITX working again. Here is a recap.? Back in March I accidently cross polarized the transceiver First thing I did was to replace both IRF510's? Q16 & Q17 That didn't work so I found that D7 Needed to be replaced. I replaced it with another 1N4007 Diode ( I think that this is intended to protect the circuit in case of cross polarization. It didn't work that in my case.? I then replaced the voltage regulator with the suggested Drok Voltage Regulator I then would turn it on and would get wisps of smoke and the smell of burning electronics. I could not locate the source of the smoke but it was coming from the area around the SI5351 and RPI. A couple of days later I pulled the SI5351 out to look at it and returned it and powered up the transceiver and there was no smoke or smell of electronics burning.? I hooked it up to an antenna and it was receiving very good, 'Next I hooked up a dummy load to it and put it in transmit and it would completely shut off immediately Next I was told that I need to set the PA Bias since I replaced the IRF510's? in order to do that I had to follow these steps:
- Set mode to USB
- Set MIC to 1
- Set Drive to 1
- Set PA-BIAS1 to Zero (Fully Counter Clockwise
- Note DC current on PTT
- Slowly increase the bias current until the total current consumed by the radio is increased by approximately 250 mA
No idea on how to measure the current with a digital multimeter so I had to do some cinematic research on how to do it. I basically had to put the DMM probe in the right socket on the DMM and put the DMM in the circuit. Here is a pic of what I did (i apologize for the crudeness of the image, I just rushed through it)?  When the sBITX is in Receive the DMM displays a 0.43, when it goes into transmit it jumps to 0.86. Before I hooked up the DMM to start adjusting the? ? ? ? ? ?PA-BIAS1 I set it to zero (full counter clockwise.) When I adjust PA-BIAS1 there is no change to the DMM readings in either receive or transmits.? This is where I'm at now and I'm unsure what tunnel in this never ending maze of tunnels to take in eventually getting this radio back on the air. I'm starting to wonder if it ever worked in the first place and my recollection of me enjoy using it is just an illusion within the confines of my cerebral carnival.?? -- '72
Aaron?
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Aaron,
Sounds like ur making headway. reverse polorizing a unit sometimes takes patience to work out all the weakened components or some that wont fail unless its under load.
I dont own the SBITX yet, but it seems from the info you provided its now isolated to the transmit sections.
I would start by looking at the si5351 area and where the Pi connect since you actually witnessed some smoke. where there is smoke, there is char, or holes in something or burnt traces. check driver transistors, and anything feeding the finals. Also check your interconnecting wires for any burn marks or punch thru holes .Since you are actually receiving stuff, i would say your si5351 and PI are good, unless the si5351 had one osc crap out .It has 3 outputs.
order a si5351board asembly which are cheap, and replace the one in your Sbitx. . Also look for any interconnecting components leading to these items on the board such as traces burnt, resistors discolored, etc. You are doing great. you got the receive up and running!!!!!! . recheck ur fets and also any driver transistors and pre amp transistors.Also check ur biasing resistors for opens.
Good luck on ur repair Aaron. You have made alot of headway since u are receiving stuff and power is flowing back into the unit.
might check your voltages on your finals , and anything up stream from the finals. Sounds like ur getting very very close.
GOOD JOB!!!!!!
73 David ac9xh
On Tuesday, June 11, 2024 at 10:42:15 PM EDT, Aaron K5ATG <aaron@...> wrote:
Hello All, Yup still trying to get my sBITX working again. Here is a recap.? Back in March I accidently cross polarized the transceiver First thing I did was to replace both IRF510's? Q16 & Q17 That didn't work so I found that D7 Needed to be replaced. I replaced it with another 1N4007 Diode ( I think that this is intended to protect the circuit in case of cross polarization. It didn't work that in my case.? I then replaced the voltage regulator with the suggested Drok Voltage Regulator I then would turn it on and would get wisps of smoke and the smell of burning electronics. I could not locate the source of the smoke but it was coming from the area around the SI5351 and RPI. A couple of days later I pulled the SI5351 out to look at it and returned it and powered up the transceiver and there was no smoke or smell of electronics burning.? I hooked it up to an antenna and it was receiving very good, 'Next I hooked up a dummy load to it and put it in transmit and it would completely shut off immediately Next I was told that I need to set the PA Bias since I replaced the IRF510's? in order to do that I had to follow these steps:
- Set mode to USB
- Set MIC to 1
- Set Drive to 1
- Set PA-BIAS1 to Zero (Fully Counter Clockwise
- Note DC current on PTT
- Slowly increase the bias current until the total current consumed by the radio is increased by approximately 250 mA
No idea on how to measure the current with a digital multimeter so I had to do some cinematic research on how to do it. I basically had to put the DMM probe in the right socket on the DMM and put the DMM in the circuit. Here is a pic of what I did (i apologize for the crudeness of the image, I just rushed through it)?  When the sBITX is in Receive the DMM displays a 0.43, when it goes into transmit it jumps to 0.86. Before I hooked up the DMM to start adjusting the? ? ? ? ? ?PA-BIAS1 I set it to zero (full counter clockwise.) When I adjust PA-BIAS1 there is no change to the DMM readings in either receive or transmits.? This is where I'm at now and I'm unsure what tunnel in this never ending maze of tunnels to take in eventually getting this radio back on the air. I'm starting to wonder if it ever worked in the first place and my recollection of me enjoy using it is just an illusion within the confines of my cerebral carnival.?? -- '72
Aaron?
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CORRECTION:This doesn't use a SI5351. What I was calling a SI5351 is actually a If anyone notices that I'm making a mistake like this or something then please correct me. I don't have a PHD in electronics and I have not been a ham who has been building this stuff for decades. Don't assume that I know it cause I don't. My goal here is to be able to get back on the air with this so I can start off learning easier to understand electronics and get more complicated as I go. Trying to figure this out, I mean yeah I'm learning some but still it feels like I have jumped in the deep end of the pool with cement shoes on.? I really appreciate all of the help that people has given me. I really don't know if I'm making more mistakes and making it worse as I go.? Now i have learned how to measure current (I even made a cable to do this) and how to replace parts, getting lots of experience in replacing parts. I try to look at the schematic and use that to find my way on the PCB but it is still way over my head.?? -- '72
Aaron?
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Aaron, you are doing great! As a former RadioShack tech, I can tell you that getting stable power in the item is always first. Although inconvenient,? this radio troubleshooting will make you an expert on the design and components.? As a teen in late 70s,? I had almost memorized the schematics of the Heathkit hw101 transceiver.? So many modifications and repairs led to that. This radio is completely different,? but keep up the good work and efforts. Document everything and be proud of your achievements.
Scotty WD4PYT
CORRECTION:
This doesn't use a SI5351. What I was calling a SI5351 is actually a
If anyone notices that I'm making a mistake like this or something then please correct me. I don't have a PHD in electronics and I have not been a ham who has been building this stuff for decades. Don't assume that I know it cause I don't. My goal here is to be able to get back on the air with this so I can start off learning easier to understand electronics and get more complicated as I go. Trying to figure this out, I mean yeah I'm learning some but still it feels like I have jumped in the deep end of the pool with cement shoes on.?
I really appreciate all of the help that people has given me. I really don't know if I'm making more mistakes and making it worse as I go.?
Now i have learned how to measure current (I even made a cable to do this) and how to replace parts, getting lots of experience in replacing parts. I try to look at the schematic and use that to find my way on the PCB but it is still way over my head.??
--
'72
Aaron?
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Aaron, like scotty said, you are doing great. I could probably put u up against a 1000 licensed hams and your new learned troubleshooting skils will probably out do 90% of them since most dont bother servicing their own equipment or experiment with their gear.
Your mis identification of parts is not too big a deal for me since i dont own the SBITX and im not a self proclaimed expert.HI HI.
This animal looks like it will help keeptrack of time and such, even? after the unit loses power because of a battery on the backside.
So , i would still look for anyshorted semiconductors in the transmit path. something seems to me was shutting ur SBITX off when you tried to key up . Meaning it was possibly dragging ur voltage down past the proper operating range. Diode, Transistor, fet, or maybe a chip tied to the +12 v or any of the other source voltages on the board ,like 5vdc, 3vdc.
If you have good receive, then get a notebook, and or print out the schematic large enough for you to follow easily. 1. you can go thru certain areas of the SBITX board and map out the voltages WHILE you are in receive mode. Then get some mini clips to attach to the board comonents and watch your voltmeter while you try to transmit. write all the voltages down for each section and or major part.
2. after you have this completed,LIke Scotty pointed out, you will have more insight into your SBITX than most have who never did this. You can then post your findings here to compare to others SBITX voltages and find the area thats causing the problem.
I would, since the unit was reversed voltaged, and you now have it up and running with receive, ?check some of the voltages on and this will take some of your time
D3,Q12,Q13,Q14,Q15, U3,,u1,u7.D2,Q5,Q3,Q9,Q10,Q11, Q16,Q17,Q18,Q19,D6 i looked at the Schematic and these "look like they are tied to the transmit section.
These can be checked by measuring "idle voltage while in receive mode and make a chart. collector,emitter base, source drain gate, diodes measure voltage on anode versus the cathode end. also after voltage checks, unplug the unit and measure the resistance of the semiconductors with the ohmmeter section. Some prefer the diode setting ,some prefer the ohms setting .
Just make a chart for each component and it might tell you whats not operating properly. having these measurements will tell others who have the SBITX whether or not you have proper voltages to these semidonductors or chips. having base? to collector or base to emitter voltages will tell if a semiconductor is properly operating with proper biasing
The unfortunate thing about reverse polarity a unit, you sometimes have to do the shotgun troubleshooting method as i call it. whatever section is tied to the transmit, you shoot thru them to identify the possible bad items by voltage resistance testing. crossing each item off the list. Since your unit shut down trying to transmit, i would think you have a Semiconductor component internally shorted or failing under load.tied to the 12vdc rail.Maybe and this is a longshot, look for any deformed capacitors. I highly doubt there are any for the short period of time you stated it was reversed polaritied, but you never know. A shorted electrolytic cap would cause this too.
after you get ur unit fully running, you might invest in a cheap priced but good reputation ESR meter to check ur electrolytic caps. preferably one that can check the "Equivilent Series Resistance "of the capacitors IN CIRCUIT. Just to make sure none have drastically changed values due to the incident.
80% of any of my service solves were capacitors that looked good but went bad for one reason or another.they mostly opened up or just plain shorted out.
Even short application of too much reverse voltage can permanently
damage the capacitor. Sometimes the self healing abilities can reverse
this a bit over time, but there will be permanent damage.
just my hillbilly take of it all.HI HI.
73 David ac9xh
On Wednesday, June 12, 2024 at 12:10:17 PM EDT, Scotty R <theroadcalls1@...> wrote:
Aaron, you are doing great! As a former RadioShack tech, I can tell you that getting stable power in the item is always first. Although inconvenient,? this radio troubleshooting will make you an expert on the design and components.? As a teen in late 70s,? I had almost memorized the schematics of the Heathkit hw101 transceiver.? So many modifications and repairs led to that. This radio is completely different,? but keep up the good work and efforts. Document everything and be proud of your achievements.
Scotty WD4PYT
CORRECTION:
This doesn't use a SI5351. What I was calling a SI5351 is actually a
If anyone notices that I'm making a mistake like this or something then please correct me. I don't have a PHD in electronics and I have not been a ham who has been building this stuff for decades. Don't assume that I know it cause I don't. My goal here is to be able to get back on the air with this so I can start off learning easier to understand electronics and get more complicated as I go. Trying to figure this out, I mean yeah I'm learning some but still it feels like I have jumped in the deep end of the pool with cement shoes on.?
I really appreciate all of the help that people has given me. I really don't know if I'm making more mistakes and making it worse as I go.?
Now i have learned how to measure current (I even made a cable to do this) and how to replace parts, getting lots of experience in replacing parts. I try to look at the schematic and use that to find my way on the PCB but it is still way over my head.??
--
'72
Aaron?
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I'm going backwards on this thing.? Now when I plug it in and turn it on, it blows the fuse in my power distribution block. Yeah it has a short but I can't find it. I keep looking at every darn component until I'm cross eyes. I doubt that it can be fixed and I'm just wasting time and money on it. I don't have much of either.? -- '72
Aaron?
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Measure the resistance of the power plug.? If it’s zero, than must likely the finals are blown. ? Tom KT4XN ? Sent from for Windows ?
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From: Aaron K5ATG via groups.ioSent: Sunday, June 16, 2024 7:18 PM To: [email protected]Subject: Re: [BITX20] Need Help setting the PA Bias Current for sBITX ? I'm going backwards on this thing.?
Now when I plug it in and turn it on, it blows the fuse in my power distribution block. Yeah it has a short but I can't find it. I keep looking at every darn component until I'm cross eyes. I doubt that it can be fixed and I'm just wasting time and money on it. I don't have much of either.?
--
'72
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It's reading Zero.? What is blowing them cause they are a week old if that -- '72
Aaron?
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You can easily blow them when you set the bias.? I’ve replaced them and popped the finals setting the bias. ? Tom KT4XN ? Sent from for Windows ?
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From: Aaron K5ATG via groups.ioSent: Sunday, June 16, 2024 8:14 PM To: [email protected]Subject: Re: [BITX20] Need Help setting the PA Bias Current for sBITX ? It's reading Zero.?
What is blowing them cause they are a week old if that
--
'72
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Ok I will replace them again tomorrow -- '72
Aaron?
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I have a v3. Ok let me understand this, I had to replace the finals and when I had to do that I have to adjust the PA Bias Current for the finals. When I adjust the PA Bias Current I blow the finals and now I have to replace them again. Once I replace them I have to adjust the PA Bias Current for them which causes them to blow.? Yeah this is a never ending rabbit hole deep into wacky land.?? -- '72
Aaron?
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Aaron,
Tom is correct. Once you fry your finals new ones installed must have the bias set to them. they will of course have slightly different characteristics due to manufacturing,etc.
When you set your Bias, before you apply power, make sure you have the bias pot set as low as possible . I dont own the SBITX but tom could tell you which way the pot needs to be turned.
after setting the bias as low as possible by turning the pot to the correct position, then after hooking up meter to measure appropriate measurements, then after double checking the finals and everything, apply power and SLOOOOOOOWWWWWLLY ADJUST THE BIAS CONTROL. AND I MEAN sloooowwwly. IF YOU CANT GET THE PROPER BIAS SETTINGS, THEN MAYBE SOMETHING ELSE IS BAD IN THE FINALS OR DRIVER CIRCUIT.EVERYONE HERE, can advise you on the correct settings and readings and the best points on the circuit to obtain them.
Just slow down, take ur time , copy and print out or write out the steps Tom and others give you and the SBITX will be on the air in time for field day if you want to test it out. plenty of hams will be listening for a contact .
frying the finals a big deal to alot of people but . plenty of replacements. and remember replacing the finals require resetting the biasing? since they probably wont be an exact perfect match.
I have popped many finals setting the bias to equipment i own. it happens to all who actually work on their own equipment one time or another.
welcome to the club,Aaron.
73 david ac9xh
On Sunday, June 16, 2024 at 09:46:59 PM EDT, Aaron K5ATG <aaron@...> wrote:
I have a v3. Ok let me understand this, I had to replace the finals and when I had to do that I have to adjust the PA Bias Current for the finals. When I adjust the PA Bias Current I blow the finals and now I have to replace them again. Once I replace them I have to adjust the PA Bias Current for them which causes them to blow.? Yeah this is a never ending rabbit hole deep into wacky land.?? -- '72
Aaron?
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Aaron, on Sbitx.net there is a detailed description on how to set ur bias on the SBITX here is what is posted there but the SBITX.NET site has loads of info for the OWNERS OF this transceiver
PA bias current
1 Set Mode toUSB
2 Set Mic to 1
3 Set Drive to 1
4 Set PA_BIAS1 preset to zero (fully counter-clockwiseBias)
5 Note DC current on PTT
6.. Slowly increase the bias current until the total current consumed by teh radio is increased by approximately 250 mA.
hope this helps Aaron, 73 david ac9xh
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Aaron,
You might double check ur fets after install. again i dont own the SBITX but make sure ur fets are properly insulated from the heat sink and the mounting screws are properly installed. might be.if the sbitx has insulating wafers instead of direct mounting, that you might have a small hole in one of them and shorting one of the fets to the heatsink.
probably could ohm the fet to the heatsink and see if you have a direct short before you apply power.
I had a problem once where the insulating bushing for the screw had broken because i cranked it too much.It cracked and the screw was shorting out the fet when powered. I was using a new screwdriver.HI HI. if the radio has this, double? check the wafer, the insulating body for the screw, etc. Just for good measures.wafer can have a hole or crack develop in it and break down due to installation. ive had insulation pads (wafers as i call them)go bad too.
73
David
ac9xh
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Take them out, then before installing the new ones, check to see if the short is gone. This is a quick way to confirm it.?
Ok I will replace them again tomorrow
--
'72
Aaron?
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Adjusting bias can in fact blow the finals, it's just part of it. THat is why equipment and procedure is important. Best is a DMM and a current limiting supply. Set the supply to give just above the current you need to run the radio plus the bias current target. BEFORE installing the new finals, make 100% sure the bias pots are set to give zero voltage on the gate pin. I also always check the voltage rise as the pot is turned to see where I think I'll be getting close.? Only then, install the finals (carefully, some are very static sensitive). Then, slowly up the bias pots while monitoring the voltage in the bias pin AND the current. The gate voltage will tell you when you are getting close to causing current?flow in the mosfet. Then slowly increase the pot until the current draw hits the target (again, the current draw with no finals installed plus the target bias current).
After blowing a couple of?+100USD mosfets, I have followed this practice and never blown another one.?
The above assumes you have checked and there are no faults in the circuit (resistors, caps, wiring in good shape). If you have another bad component, it can blow the finals quickly. A friend had a set of finals blown when the wire winding on the output transformer chaffed and shorted?to ground for example. It can be done without the current limiting supply, but the current limiting supply provides insurance against bad components or procedures.
Andre? W4SFZ
I have a v3.
Ok let me understand this, I had to replace the finals and when I had to do that I have to adjust the PA Bias Current for the finals. When I adjust the PA Bias Current I blow the finals and now I have to replace them again. Once I replace them I have to adjust the PA Bias Current for them which causes them to blow.?
Yeah this is a never ending rabbit hole deep into wacky land.??
--
'72
Aaron?
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On Sun, Jun 16, 2024 at 09:55 PM, david todd wrote:
PA bias current
1 Set Mode toUSB
2 Set Mic to 1
3 Set Drive to 1
4 Set PA_BIAS1 preset to zero (fully counter-clockwiseBias)
5 Note DC current on PTT
6.. Slowly increase the bias current until the total current consumed by teh radio is increased by approximately 250 mA.
hope this helps Aaron,
73
david
ac9xh
I think this is old info for the IRFZ24N mosfets. Is the current differential the same for IRF510's?
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?
... how much is approximately the Gate voltage if the common quiesent
current is about 200 mA ???
( ... 3,4 volts ???)
?
73 , Jens / HB9JOI
?
+++
?
toggle quoted message
Show quoted text
From: JJ -
W9JES
Sent: Monday, June 17, 2024 7:09 PM
Subject: Re: [BITX20] Need Help setting the PA Bias Current for
sBITX
?
On
Sun, Jun 16, 2024 at 09:55 PM, david todd wrote:
PA bias current
1 Set Mode toUSB
2 Set Mic to 1
3 Set Drive to 1
4 Set PA_BIAS1
preset to zero (fully counter-clockwiseBias)
5 Note DC current on
PTT
6.. Slowly increase the bias current until the total current consumed
by teh radio is increased by approximately 250 mA.
hope this helps
Aaron,
73
david
ac9xh I think this is old info for the
IRFZ24N mosfets. Is the current differential the same for IRF510's?
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The gate Voltage varies from lot to lot.? There are two numbers gate threshold
voltage and? Transconductance usually, in siemens.
The gate threshold voltage is in the range of 1.7 to 3V.? I tested 10 and most
were in the 2-3V range but at 2.5V some barely turned on and two were at 1.8A.
So max gate voltage will be under 4V and over 1V.? The variation is also seen
on commercial RF devices as wel.
The first the threshold voltage is the point when the MOSFET starts to conduct.
The second is basically the gain of the device and the ratio of gate voltage change
to drain current.
What it means is change the mosfet change the bias.? There is no fixed use this voltage
for a given drain current.
--
Allison
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Please use the forum, offline and private will go to bit bucket.
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Aaron K5ATG
Scotty R
WK4DS
Jens/HB9JOI