You're very welcome. My wife does crosswords for fun, but these challenges more to my liking. They are procrastinations from waiting chores. And I fear I'm living vicariously through you guys who are spending time on the bench. 😉
I need to think about your latest data and what to suggest next.
I was about to suggest that you remove CR4 as a diagnostic and recalled from post 25 that you had removed them both. Still MIA in both channels? With CR4 absent, the current limit circuit cannot intervene in regulator control. That's a convenient simplification in trouble shooting.
Remaining in the current limit arena for a bit, re post 59, if schematic is to be trusted, R15 is 240K and R14 is 3.3 ohms. From pic, I can't be certain of resistor in the pic. Bands might indicate 3.3 ohm. Not sure how to reconcile with your resistance measurements.
With A5 floating, Q2A transistor should not be conducting, so Q2 tail current should be flowing through Q2B, yielding about 1.5V at TP16. But you report TP16 is 3.48V, suggesting Q2B not conducting and that CR4 is in place. All unresolved at present. Perhaps Q2 has failed. If CR4 is absent, you could report all Q2 terminal voltages for insight in this area.
If CR4 is absent in one of the channels, perhaps it would be the most convenient section for attack? That would allow an attack on voltage control problems.
Remaining in the current limit arena for a bit, re post 59, if schematic is to be trusted, R15 is 240K and R14 is 3.3 ohms. From pic, I can't be certain of resistor in the pic. Bands might indicate 3.3 ohm. Not sure how to reconcile with your resistance measurements.
With A5 floating, Q2A transistor should not be conducting, so Q2 tail current should be flowing through Q2B, yielding about 1.5V at TP16. But you report TP16 is 3.48V, suggesting Q2B not conducting and that CR4 is in place. All unresolved at present. Perhaps Q2 has failed. If CR4 is absent, you could report all Q2 terminal voltages for insight in this area.
If CR4 is absent in one of the channels, perhaps it would be the most convenient section for attack? That would allow an attack on voltage control problems.
CR4 is replaced on the unit being tested.
It is R14 and you are right it is color banded for 3.3 Ohms. (I took the gold band for brown.)
R14 measures 5.2 Ohm from the bottom of the board.
R16 is color coded 240K but is reading 5.28Kohm from the bottom of the board.
CR4 is missing in the second unit. You want to run tests on that one too?
I'll run the simple multimeter tests on Q2A&B that techtool suggested way back.
It is R14 and you are right it is color banded for 3.3 Ohms. (I took the gold band for brown.)
R14 measures 5.2 Ohm from the bottom of the board.
R16 is color coded 240K but is reading 5.28Kohm from the bottom of the board.
CR4 is missing in the second unit. You want to run tests on that one too?
I'll run the simple multimeter tests on Q2A&B that techtool suggested way back.
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Q2A =
E B C
# 139K 15.8K
E B C
140K # 157K
E B C
15.5K 147K #
Q2B =
E B C
# 8.6K 14.4K
E B C
8.5K # 9.6K
E B C
14.4K 9.2K #
E B C
# 139K 15.8K
E B C
140K # 157K
E B C
15.5K 147K #
Q2B =
E B C
# 8.6K 14.4K
E B C
8.5K # 9.6K
E B C
14.4K 9.2K #
That is strange. The voltage readings you've reported seem reasonable, though I've not calculated what they should be based on schematic. If you're unsettled by the resistance discrepancy, try reversing ohmmeter leads and see if you get identical readings. There may be semiconductor paths shunting the measurement. Other other paths may be in play. You may have to lift one lead so that you can make an isolated measurement.
I'm sorry, but I don't know how to use the data in post 64. Voltage measurements at Q2 with A5 open and CR4 lifted should tell me about the health of Q2.
Having CR4 lifted is useful because it disables the current limit path, leaving only voltage control control. For background, see sections 4-18,4-29, and Table 5-4, step 2.
If the other channel already has CR4 removed, maybe trouble shooting its voltage regulation problems is a way to proceed and gain familiarity.
This is your equipment and not my rodeo to direct. 😉 Any preferences?
I took CR4s out to test with current limiting disabled. Didn't see a change but will retest.
I am going to start the Table 5-5 High Output Voltage Troubleshooting and see if that finds the problem.
I read someone smoked a 6253A saying that it is a linear that cannot tolerate sinking current.
What does one need to do to avoid that sinking current? (I read some about sinking & sourcing current but am hoping to avoid spending more time right now. Just want to avoid doing it by mistake to this power supply.) He said he did it charging a battery?
What does one need to do to avoid that sinking current? (I read some about sinking & sourcing current but am hoping to avoid spending more time right now. Just want to avoid doing it by mistake to this power supply.) He said he did it charging a battery?
A battery could source current into the the power supply (i.e. supply is sinking), and that might cause damage. This supply certainly isn't intended to absorb/dissipate large currents.
Your testing won't involve anything like that. And having current limiting disabled isn't an issue because you won't be applying any heavy loads. Once voltage control is working correctly, you'll return to the current-limit section.
I think pursuing Table 5-5 will lead you in the right direction. I'm happy to try helping along the way.
Your testing won't involve anything like that. And having current limiting disabled isn't an issue because you won't be applying any heavy loads. Once voltage control is working correctly, you'll return to the current-limit section.
I think pursuing Table 5-5 will lead you in the right direction. I'm happy to try helping along the way.
Thanks BSST
I've pulled a few components but am going to run over everything with a multimeter next.
Q6 shows hFE 88, Ube 506mV, Ic 6.4ma
No idea if this is good since it's like many HP parts with no specs.
I ran across this Aussie salvaging a PS: (must be talking to techtool) 🙂
"A simple multimeter will reveal semiconductors and capacitors that have become short circuits and resistors that have aquired impossible resistances and also obvious short circuits where they are clearly not required. At least 80 % of electronic faults can be diagnosed and repaired this way, even without possession of the circuit or even having to understand the design."
https://users.monash.edu.au/~ralphk/hp6282.html
I've pulled a few components but am going to run over everything with a multimeter next.
Q6 shows hFE 88, Ube 506mV, Ic 6.4ma
No idea if this is good since it's like many HP parts with no specs.
I ran across this Aussie salvaging a PS: (must be talking to techtool) 🙂
"A simple multimeter will reveal semiconductors and capacitors that have become short circuits and resistors that have aquired impossible resistances and also obvious short circuits where they are clearly not required. At least 80 % of electronic faults can be diagnosed and repaired this way, even without possession of the circuit or even having to understand the design."
https://users.monash.edu.au/~ralphk/hp6282.html
No guarantees of course, but the Q6 numbers look reasonable. Did Table 5-5 lead you in this direction?
Aussie is probably correct, but I prefer in-circuit, powered diagnosis. There's a bit less risk of damage and it's more fun to probe the circuit and figure out how it works. But in the end, it's frequently guided guess-work component replacement.
Good luck!
Aussie is probably correct, but I prefer in-circuit, powered diagnosis. There's a bit less risk of damage and it's more fun to probe the circuit and figure out how it works. But in the end, it's frequently guided guess-work component replacement.
Good luck!
Thanks again BSST
Since output voltage is high, I interpret Table 5-5 to say the issue is likely Q6, Q7, CR11, etc.
I decided to check Q6; then I got trying to figure out what specs Q6 had. Failing that, I
found them as NOS for $14 apiece or so.
Don't seem to need a replacement, as you confirmed, so that was a waste of time.
I was confident that pursuing the voltage specifications like we did would lead to the solution but that was inconclusive.
I'll use the multimeter method too but I'll Q7 next too.
Since output voltage is high, I interpret Table 5-5 to say the issue is likely Q6, Q7, CR11, etc.
I decided to check Q6; then I got trying to figure out what specs Q6 had. Failing that, I
found them as NOS for $14 apiece or so.
Don't seem to need a replacement, as you confirmed, so that was a waste of time.
I was confident that pursuing the voltage specifications like we did would lead to the solution but that was inconclusive.
I'll use the multimeter method too but I'll Q7 next too.
I managed to break a lead on CR11 while taking it out. The TC1 tester shows uF=570mV, c=275pF, Ir=6nA
The solder sure seems hard to melt. HP says to heat from the top but I sure don't see how for a lot of the components.
The solder all the way through the board maybe makes it harder? idk
I ordered the Hakko FR-301 desolder tool. Hopefully that will cut down on damage. 🙂
The solder sure seems hard to melt. HP says to heat from the top but I sure don't see how for a lot of the components.
The solder all the way through the board maybe makes it harder? idk
I ordered the Hakko FR-301 desolder tool. Hopefully that will cut down on damage. 🙂
I believe CR11 is a generic diode to protect Q6 from reverse voltage; assuming it's not a high-current device, a 1N200X should suffice.
You have my sympathy. We can try in-circuit trouble-shooting again if you wish. What you're experiencing is why I'm loathe to remove a component unless I'm extremely suspicious it's faulty--- I've been there, more times than I care to think about.
You have my sympathy. We can try in-circuit trouble-shooting again if you wish. What you're experiencing is why I'm loathe to remove a component unless I'm extremely suspicious it's faulty--- I've been there, more times than I care to think about.