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carlitosbala
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Last Activity: Today, 04:20 AM
Joined: 02-22-2021
Location: XX
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  • I had forgotten about this thread

    Thank you for your reply, I ended up taking the calculator to an electronics repair shop for diagnostic to avoid causing more damage while testing. The guy at least confirmed the power supply board looks OK, but apart from that was unable to find a fault and just told me that IC is bad and I should try to get a replacement.

    I'm tempted to try removing it from the board and powering it, in my mind the best case scenario is the calculator should work and just have one of the digits not showing. If the IC is shorting the circuit to ground...
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  • Elektronika EPOS-73A stuck with fixed display

    Hi,

    I'm hoping I can get some ideas on what to check in this old (1978) soviet-era electronic calculator I got from a flea market, the Elektronika EPOS-73A.

    Got it home and plugged it in. It worked just fine at first, I used it a few times for a few minutes each time, "kid with new toy" style.

    Then I disassembled it to clean the plastic case and the keys. I couldn't separate the lower half of the case from the board because cables are tied to it, so during the cleanup one of the cables going from the power board to the main board detached,...
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  • Re: MS-6590 KT4 Ultra - short on vcore

    The second mobo is an M7VIG 400. Both this and the KT4 Ultra support 200, 266, and 333 MHz FSB CPUs according to their manuals

    The CPUs I have should be supported: the models are
    2 x SDA2200DUT3D (Sempron 2200+, Thoroughbred, 333 MHz FSB)
    3 x AX2000DMT3C (Athlon XP 2000+, Palomino, 266 MHz FSB).

    The one I got to work is one of the Semprons.

    I learned the hard way that the KT4 was actually doing the right thing by shutting down, the M7VIG happily fried (burned plastic smell included) three other...
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  • Re: MS-6590 KT4 Ultra - short on vcore

    Sorry about that. the right link was [url]https://www.badcaps.net/forum/showthread.php?t=38368[/url], the ID I used was for a specific post within that thread.

    In any case, the initial advice I was given here was spot on, and I should have listened to it. As soon as I put a proper heatsink and fan on top of the CPU I got the motherboard to stay on. Live and learn...

    Unfortunately now I don't know if I have a working CPU to test. I got a second motherboard with the same socket, and of the 5 CPUs I have that should be...
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  • Re: MS-6590 KT4 Ultra - short on vcore

    Alright, I did another testing session today and I *think* I have identified a problem with the ATTP1 chip.

    I approached the problem with the idea that it was a thermal shutdown. So I started looking at the signals involved, and searching for "THRM_PSON" led me to [thread=612720]this thread[/thread], which I still need to read in detail as it has a very good description of how this part of the board works. Mine is not the same model, but almost all the components described connect to the same signals, and is similar enough...
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    Last edited by carlitosbala; 06-03-2021, 10:10 PM. Reason: improve description of the problem

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  • Re: MS-6590 KT4 Ultra - short on vcore

    Just as an update: I got some goodies from the US recently that I have been waiting for, including a cheap ESR meter, a cheap PCI test board, and enough capacitors for the motherboards I still think I can fix, like this one. I could have bought locally but the biggest distributor of electronic components in Montevideo charges more or less the same than what I payed at Newark including shipping.

    So I went and recapped this board, and still get the same result. The old caps didn't really show any issues in the esr meter: capacitance...
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  • Re: MS-6590 KT4 Ultra - short on vcore

    I had a bit more time to check this board again.

    I was re-testing what I had already tested, like making sure vcore is actually being generated before the board shuts down, at pin 10 of the U6 chip and in the positive terminal of the capacitors between vcore and ground.

    As I don't want to overload my PSU, I shut it down after every test. After one of the tests I forgot to switch it off while I fixed some issues I had with my monitor, and after a few minutes the fan started spinning again, normally.

    In...
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    Last edited by carlitosbala; 04-06-2021, 09:25 PM.

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  • Re: MS-6590 KT4 Ultra - short on vcore

    Thank you for the follow-up, I did notice the board was a different one (in fact I do have a working board of that model!), but I assumed you referred me to it as an example of the things I could try.

    I started looking at the schematics to find signals to verify, so thanks for the pointers. I haven't had time yet to go back to this board, but will resume the troubleshooting soon.

    Regards
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  • Re: MS-6590 KT4 Ultra - short on vcore

    @dicky96: point taken. Forget about the short

    I don't have a bench PSU yet, I will get one as soon as my budget allows it

    As I mentioned before I'm a beginner, that means I may fail to see a problem more experienced technicians would identify immediately. I have no issue admitting it, but I tend to clarify it so the people I ask for advice doesn't assume that I may have done / checked anything in particular

    I believe I'm quite good at reasoning, and I can read a schematic, so I hope that if...
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  • Re: MS-6590 KT4 Ultra - short on vcore

    I'm about to give up on this one, I don't know what to check, and seriously considered removing each and every capacitor between vcore and ground, but there are just too many of them, and I have never soldered an smd component, so I'll definitely screw up if I go that route. Not that I have anything to lose anyway.

    I was looking at the board and found these FM points, listed in page 46 of the schematic, what are they? Can I use them to diagnose parts of the board?
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  • Re: MS-6590 KT4 Ultra - short on vcore


    Well, I've bought several boards to play with, all in the 486 - Pentium4 range, and my idea is to restore at least one of each generation, including a complete recap for the ones that I can get to work. So replacing those is part of the grand plan

    Noted. I do have a heatsink I put on top of the cpus I'm testing when I turn on the power, so I'm not letting it overheat (I hope). I've only had this board+cpu for a couple of months and to be honest I can't be sure the CPU is OK, my only kind-of-assurance is that I have...
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  • Re: MS-6590 KT4 Ultra - short on vcore


    Attached a photo. Any part you want me to show in more detail?

    Could you please explain this a bit more? I mean, i know you mean removing the chokes and testing, but I'd like to learn the background behind the suggestion and what test do you want me to do

    Regards...
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  • Re: MS-6590 KT4 Ultra - short on vcore

    The resistance without CPU doesn't increase, it stays at that value.

    I forgot to mention something: if I measure the voltage on pin 2 of the 6022 (PWM2) and turn on the board, I get to read a voltage of 1.8V before the board shuts down.

    And just to clarify: I'm not seeing the usual "fan moves for a split second and you miss it if you blink", what I see is the board turning on for a full second or so and then shutting down.
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  • Re: MS-6590 KT4 Ultra - short on vcore

    Without: 27.3 Ohm, with: 13.2

    Measured it from the chokes in the VRM to a ground point from one of the screws
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    Last edited by carlitosbala; 03-24-2021, 08:26 AM.

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  • MS-6590 KT4 Ultra - short on vcore

    Hi,
    I continue my journey trying to learn how to repair a motherboard, I still have a few after the Netvista ended up working

    I am trying to fix an MSI MS-6590 KT4 Ultra, that I discovered has a short on Vcore.

    The board turns on without issue if the cpu is not installed, but it turns off after a few seconds with the CPU on.

    After analyzing the schematics (attached) I found the vcore output in page 39 (Voltage Regulator Module) is shorted to ground. I took every component referred to in that page out of the board for testing and they are all...
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  • Re: IBM Netvista 6790 - not booting

    Thanks, piernov, for your advice.

    I had put the machine in storage before creating this thread, after spending around 6 hours (couple hours each day for a few days) looking at it and trying to find documentation. I set it aside because I have other boards to play with and this one was not fun anymore.

    Yesterday night, after your suggestions, I again opened the machine, prepared the board for yet another check with just the power connected, and started checking with my multimeter around the *bridges. I did find the voltages...
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  • Re: IBM Netvista 6790 - not booting

    Thanks for the tips. I should have looked at it: I'm ashamed that I thought sSpec was a typo lol

    P4
    1.8GHz/256/400 1.75V SL5VJ <- I'm quite sure this is the one the machine had, but it has been a while since I dissassembled it.
    2.40GHz/512/800 SL6WF

    Celeron
    2.40GHz/128/400 SL6VU
    1.7GHz/128/400/1.75V SL68C
    1.80GHz/128/400 SL876

    I tried three different PSUs, with the same result. There are no beeps without the RAM.
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  • Re: IBM Netvista 6790 - not booting

    They all come from machines that weren't mine and I don't have a working 478 board, so for all I know they might be dead.

    3 of them are Celerons: 1.7/128/400, 1.8/128/400, and 2.4/128/400.

    Two are P4s: 2.4GHz/512/800, and 1.8/256/800.

    The 1.7 Celeron and the 1.8 P4 also say 1.75V
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    Last edited by carlitosbala; 02-24-2021, 06:15 PM.

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  • IBM Netvista 6790 - not booting

    Hi All,
    I'm new in BadCaps, so I hope this is the right forum to make my question.

    I come here because I have an IBM NetVista 6790 that doesn't boot.

    I have always liked to tinker with PCs but only recently started trying to get into component repair, so I know how to check a PC but I'm at a loss without schematics on what to check when things are not obvious (i.e. a shorted mosfet). Also, I am sure there are a lot of symptoms that for someone experienced will point directly to the issue, but I don't know how to identify.

    So this machine doesn't...
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  • Re: New Members - please post your introductions here

    Hi, my name is Carlos and I'm from Uruguay. I work with infrastructure in AWS and pc repair is a hobby I am trying to get a bit deeper into. Glad to join the community
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