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HP 6632B PSU showing CV and CC at the same time
Hi!
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I recently repaired a 663120A where the crow-bar just kicked in and did it's job. The trouble was to find the right soldered in mini-fuse that was half way hidden under the interface board.
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So I hoped for an easy fix on my 6632B too but no. I tried to follow the failure diagrams in the service manual and just got the info to replace the interface board. But the signals on the interface to that board do show a lot of good and only a few out of range values. Especially the signals that should make the display show CV and CC are active, so the interface board is right.
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The fault itself is, that I can enable the output of the unit as long as I program 0V. As soon as I try to program more then about 0.7V the system shows CV + CC at the same time and no output voltage.
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The measured voltage on the VFD is close to my multimeter, so the ADC seems to work.
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One thing I recognized is, that the input bus voltages are all high. But I double-checked that the transformer ist configured for 230V. But the (+) rail has 45V compared to the service manual saying it should have 39V. The (-) 9V rail has -12V. Is there anything known about a faulty series of transformers or a bug in the wiring diagram?
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73 de Ulrich
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Re: Tantalum Capacitors
I think Adrian is doing a good job in going slowly through the analysis. Sometimes you get the wrong way and that happens to all of us. Making interesting episodes is one thing, but having to repair something in time as the customer is waiting outside is another one.
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Like Usagi and others channels, as an old guy sitting in front of the screen, there are these moments where you scream at them, telling "There is the fault right in front of you!" but the guy on the screen is going the whole wrong way. But that is part of the fun.
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Back to the capacitors I have successfully replaced Tantalum types by Aluminum Polymer. These combine the benefit of being dry and having a low ESR. Even dry electrolyte sounds great and you want to replace all caps by this type, there are problems. You can replace Tantalum bei Al-Poly as the PSU is prepared for low ESR caps or there are small resistors in front of them (sometimes there are coils in front that filter but also add enough serial resistance)?
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Replacing Al-Electrolyte with Al-Poly will result in a big punch on the PSU on power-on but not as hard as if you replace low value AL-Electrolyte by MLCC ceramics. So the PSU needs to be prepared for that. And there is no way to replace Al-Electrolyte with AL-Poly in signal related places except you adapt surrounding inductance or resistance values.
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In any smaller test equipment like power-meters and such, especially when the supply is linear regulated, Al-Poly is good. But if you replace all more than 300 Al-Electrolytes by Al-Poly in a Stabilock 4031, you might trigger overload on power on of the PSU.?
But again, if you replace the 10uF caps on the 4031 CPU and secondary CPU board by 1uF Al-Poly or MLCC, that should work absolutely fine, as the series resistance is much lower and the energy required is transferred much faster. But the punch on the PSU is shorter and lower because of the reduced capacity. The Al-Poly will not go up in flames like to original ones and not peeing on the board like wet caps and eating the traces.
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And then again, replacing all SMD electrolytes in the small Stabilock 4015 by Al-Poly will cost over 170€ and may introduce different problems. Using Automotive or Aerospace certified Al-Electrolytes from the best brands you can get, will cost less then 80€ and make the unit work again for the next 40 years. And there is still hope, that modern Al-Electrolytes do not leak and eat your traces from the PCB, as the capacitors from the 2000'ds do when the capacitor plague was a thing.?
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73 de Ulrich
DC3AX / AG1U / OE3UPR
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Re: HP141T with multiple sections
Many thanks David and Gary, so I guess best not take any risk, I'm going to power up my HP141T with one full set of section: 8552B and 8553B plus the great active probe 1121A which I've forgot to mention. Let's hope its stoarge for more than 2 years will not affect any PSU, electrolytic power cap and so.
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In the mean time, I was looking in our forum for HP141T key words then found this very interesting old comment on LCD retrofit kit
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Looked briefly to what was done on the ? it is suddenly mind blowing how the 70's HP141T has been colorized, other display possibilities, this is awesome.
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Suppose I remove the CRT unit and electronics from my HP141T to replace with a LCD kit, do you know how much weight in kg would be saved and power consumption gained ?
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I saw on the Rohde&Schwarz forum someone who used the same LCD-FPGA demo board kit to replace a CRT unit, not sure where I saw this but it is the same situation with TD500/700 oscilloscope and Advantest R3261/R3361/R365/R3365/R3271/R3371, the cost or impossible to find old CRT => the challenge to LCD retrofit which permits to colorize, add new function if proper hacking of the legacy board.
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Re: HP141T with multiple sections
This depends on the age of the mainframe, late ones have a interlock connection & relay in the power supply, to prevent operation with no plug-ins fitted.
But for testing something in unknown condition, I prefer to make sure the power supply rails are correct before fitting plug-ins, this also applies to the 18x series mainframes.
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David
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On Tue, Dec 3, 2024 at 09:42 AM, tantratron wrote:
My first question: since the HP141T was not run for more than 2 years, is it possible to run the HP141T alone with no section added. |
DC3AX
Anders
tantratron
RubenRubio
factory