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Vintage Computers Any vintage computer systems, calculators, video games etc., but with an emphasis on 1980s and earlier equipment.

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Old 24th Feb 2017, 1:05 pm   #1
lightfoot
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Default Help required to repair vintage computer. FIC 486 G10 VT2.

Can anyone help me in repairing this computer as it is still required to be used as a server and also for the use of existing hardware, fault is that the cmos setup will not save entered settings (battery "new" has been changed) also it auto sets the hard drive (one only) which on a correctly working 486 would only have "user" and numbered types offered, I bought this to replace a previous motherboard as "working" which of course with it crippled is of no use so I'm looking for someone to help me out by posting an address of someone trustworthy in Wales preferably to get the motherboard repaired.
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Old 24th Feb 2017, 2:27 pm   #2
kellys_eye
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Default Re: help required to repair vintage computer fic 486 g10 vt2

Check the link beside the CMOS battery/BIOS device. It may still be in the 'clear BIOS settings' position.
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Old 24th Feb 2017, 3:23 pm   #3
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Default Re: help required to repair vintage computer fic 486 g10 vt2

Have you checked the voltage of the new battery? Faulty examples do exist, see the recent thread about lithium cells on the forum.
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Old 24th Feb 2017, 3:27 pm   #4
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Default Re: help required to repair vintage computer fic 486 g10 vt2

Thanks for your reply however J7 which is use to clear the bios setting was checked so this is not the problem. Being as you replied may I explain further. When I received the motherboard from the seller (no returns excepted) the motherboard was not as advertised. Two differences being that there was no cmos battery, and the original sticker on the bios chip had been removed with a small sticker with HP4.Bin, meaning to me that the chip had been flashed. It would seem that the previous user when the cmos setup stopped working had flashed creating a bootable no unalteratable single hard drive pc.
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Old 24th Feb 2017, 3:30 pm   #5
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Default Re: help required to repair vintage computer fic 486 g10 vt2

Nickthedentist, Thanks for your reply, yes did check this and tried a few more and tested them all with my multimeter.
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Old 25th Feb 2017, 1:53 am   #6
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Default Re: Help required to repair vintage computer. FIC 486 G10 VT2.

How about the bios itself- can you re flash it?
Although finding the software for it might be a problem now, but some MB manufacturers have archive files going back a long way.
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Old 25th Feb 2017, 8:24 am   #7
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Default Re: Help required to repair vintage computer. FIC 486 G10 VT2.

Given the BIOS can be 'entered' (in order to change-but-not-save settings) I suspect the BIOS itself to be OK but the 'external' settings are saved to CMOS which is patently not maintaining content either through a faulty chip (unlikely) or some defect in the battery backup circuitry.

An inadvertently reverse-installed battery could destroy the steering diode associated with maintaining the memory-retention voltage which would be the first area of the circuit I would be looking at for a fault of this type.

The next area would be to look for a defective supply decoupling capacitor on the CMOS device supply rail.

Last edited by kellys_eye; 25th Feb 2017 at 8:30 am.
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Old 25th Feb 2017, 8:42 am   #8
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Default Re: Help required to repair vintage computer. FIC 486 G10 VT2.

Another thought - sorry if this one seems too 'simple' - are you using the correct key combination to make the changes 'stick'?

If the BIOS has been flashed it may result in the 'usual' keystrokes being changed to something different - and force-of-habit 'hit F10 to save changes' (or whatever) may no longer apply. Long shot but worth checking.
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Old 25th Feb 2017, 11:33 am   #9
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Default Re: Help required to repair vintage computer. FIC 486 G10 VT2.

The bios update is available, cheefulcharlie and have downloaded in case I can solve the reason why the cmos battery is not supplying the voltage required for the cmos setup utility to work as described by Kellys eye also regarding the keystokes ie F10 to save changes I have saved from within the setup utility which indicates that the change has taken it is only when you revisit the setup utilty on bootup that you then notice that nothing has been changed which brings me back to the circuitry which unfortunately my ablity to find this fault is limited hence the request for help from someone else.
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Old 25th Feb 2017, 1:13 pm   #10
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Default Re: Help required to repair vintage computer. FIC 486 G10 VT2.

Can you post a close up picture (hi-res) of the area around the CMOS battery. Worst case we could try to point to the device(s) to make basic tests on and if you can't replace the device yourself then it would be an easier task to find someone to do the actual replacement.
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Old 25th Feb 2017, 8:00 pm   #11
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Default Re: Help required to repair vintage computer. FIC 486 G10 VT2.

Thanks Kellys eye will try to get the best picture I can and if i can't do what is required hopefully someone can help in finding someone to do the replacement of the part or parts.
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Old 25th Feb 2017, 8:21 pm   #12
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Default Re: Help required to repair vintage computer. FIC 486 G10 VT2.

Have a problem regarding the picture as I don't know how to place it within a message...can I use the link to ebay where an identical motherboard is on offer as I see there is provision to attach a link, hope I'm right as I'll try it and see what happens. http://www.ebay.com/itm/FIC-486-GIO-...-/181643382202 let me know if I got it right,Thanks again for your help.
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Old 25th Feb 2017, 8:32 pm   #13
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Default Re: Help required to repair vintage computer. FIC 486 G10 VT2.

The close-up picture of the coil cell shows two diodes at the 2 o'clock position which are used to 'steer' the battery voltage hither and thither and should be checked (power off, battery removed) using a test meter set to it's 'diode check' range (the instructions with the meter should tell you all you need to know about testing diodes in this way). I suspect one of the (the larger of the two) is open circuit.

Unfortunately the pictures of the area closer to the BIOS and CMOS memory aren't in the enlarged images so I can't be more detailed about anything else at this time.

Before doing the electrical test, have a REAL CLOSE UP look at the larger diode and give it a gentle 'poke' to see if the body has cracked - such diodes are easily damaged if the battery is 'dropped' onto it or pushed against it due to misalignment or accident.
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Old 26th Feb 2017, 1:02 am   #14
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Default Re: Help required to repair vintage computer. FIC 486 G10 VT2.

How about resetting the date to 1997 or something ..see if there is an issue with built in obsolescence?
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Old 26th Feb 2017, 10:50 am   #15
lightfoot
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Default Re: Help required to repair vintage computer. FIC 486 G10 VT2.

in answer to you cheerfulcharlie the cmos setup utility when opened up has the date 1/1/94 and any time is zero'ed and the clock restarts , any date or time saved reverts back to this and any other alterations like hard drive parameters for the second drive, as already mentioned the first drive is auto detect and shown as USER once loaded again. back to kellys eye have already checked the diodes mentioned and both seem to be undamanged, thougth that it might be a dry joint and resoldered them from the other side of the board without success, with the battery in no output from both diodes ? at this I'm stuck!
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Old 26th Feb 2017, 11:13 am   #16
lightfoot
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Default Re: Help required to repair vintage computer. FIC 486 G10 VT2.

may I thank both of you for helping me here, perhaps with your help we will be able to sort this out either with you both our at the last resort someone that has been recommended off site.At the moment the board is installed in the case and will need to remove it and set up on test bench to go back over it again though at this point I'm feeling quite despondent.
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Old 26th Feb 2017, 1:31 pm   #17
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Default Re: Help required to repair vintage computer. FIC 486 G10 VT2.

If you Google for Motherboard CMOS back up battery schematic (or some such) you'll see various examples of how they are (generally) wired and gain some idea of what you need to be looking for.

The basic process is the CMOS connected to the backup supply pin via a pair of 'wired-OR' diodes - one diode prevents the 5V feeding into the backup battery (since, when the PC is powered up, the cathode is at 5V and the anode at 3.2V thus reverse-biasing it) and another stops the CMOS battery voltage feeding back to the 5V line when the power is off.

You should be able to identify the CMOS memory device and, from the easily-available datasheet for it, identify the 'keep-alive' voltage pin.

Measure this supply with the PC powered on (should be around 5V less the forward drop of the diode) and with it powered off (where it should revert to the CMOS battery voltage - less the volt drop of its isolating diode - probably only a small drop as this diode tends to be a low volt-drop version).

If the battery and CMOS memory are fairly adjacent then tracing the track - even if you have to revert to a continuity check - should be straightforward.

If you suspect dry joints anywhere in the area then resoldering ALL joints is simpler than isolating the dodgy one.
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Old 26th Feb 2017, 1:39 pm   #18
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Default Re: Help required to repair vintage computer. FIC 486 G10 VT2.

I think I could see the RTC chip number (DS12885) in the eBay image and the pinout for it is as shown in the attached picture where you can see the Vbat pin (24) as the point you need to measure to see if the backup battery is reaching that chip.

Not sure how the CMOS backup is implemented on that board but there is some general purpose RAM within the RTC device that may be the area where setup details are saved therefore losing the supply to this device will lose the CMOS setup details.

If you measure Vbat (with power on and off) and it is within acceptable limits then check for a signal from the crystal. If this is similarly ok then the chip may be dud. It's difficult - but not impossible - to replace this device given it's not as small as modern SM stuff! using 'cut the leads, desolder the mess and fit a new one' method.
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Old 26th Feb 2017, 3:02 pm   #19
lightfoot
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Default Re: Help required to repair vintage computer. FIC 486 G10 VT2.

Thanks again for your prompt follow on. i have prior to this reply spent about an hour looking for a cmos schematic without luck, as my ablity is some what limited I'm feeling somewhat confused as your technical description is not getting through to this old head of mine, I understand that with power on the boards voltage would be 5v and on battery 3v where I'm lost is where you say "If the battery and cmos memory is adjacent" ..cmos memory where? you went on to say about the RTC and Vbat pin 24 I believed that as in the cmos setup utilty under the psu voltage is is marking time meaning it is working.
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Old 26th Feb 2017, 5:12 pm   #20
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Default Re: Help required to repair vintage computer. FIC 486 G10 VT2.

Just to qualify this process - do the clock settings 'save' ok? If so then the backup battery circuitry is ok.

If not then you need to check that the retention voltage appears on pin 24 during (a) power down (3V) and (b) power up (5V).

If you can identify the BIOS chip device itself and let me know its device number then we can determine if the data is stored on it as EE (electrically-erasable) or in a different fashion.

If the settings are saved to the BIOS device itself then by eliminating the external reset circuitry as the potential cause of it 'permanently clearing' the content we can determine if the BIOS chip itself is defective.
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