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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 26th Feb 2017, 6:21 pm   #21
lightfoot
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Default Re: Help required to repair vintage computer. FIC 486 G10 VT2.

Hello again, first the clock settings do not save nor the date or any other settings, when I do a tear tomorrow and rebuild outside the case I'll check the voltage on pin 24 (RTC) unfortunately the original award sticker has removed and replaced with a small blue sticker with HP4.BIN so with this on it I would assume that as flashable EE as for a different fashion I do not know, as the entered settings are not saved to the Bios device I can only suspect that the cmos battery circuity is the fault as to use the external reset J7 in this case causes the password cleared to appear and request to remove afterwards..
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Old 26th Feb 2017, 9:17 pm   #22
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Default Re: Help required to repair vintage computer. FIC 486 G10 VT2.

The BIOS device number will be etched onto the chip itself, not as a 'label' - which will have to be removed to see the actual device number.

If the RTC and BIOS aren't retaining data they may either not be 'receiving the data' in the first place (meaning a chip select signal error), losing the data thereafter (battery retention problem) or not storing it at all (permanent 'clear data' level on the appropriate pin). The highest level of failure would be potential EEPROM 'failing' but the fact that the RTC also loses data makes this situation somewhat less likely.

Each potential problem can be tested using basic equipment (with the chip select one being the most difficult, requiring a means of analysing the CS (or CE) line with a storage scope or data analyser) but the battery and 'clear data' events are simple tests via multimeter.

If you can get me the BIOS device number I'll be able to develop a simple schematic that illustrates the principles of operation and make understanding of what is happening clearer.
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Old 27th Feb 2017, 10:31 am   #23
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Default Re: Help required to repair vintage computer. FIC 486 G10 VT2.

When you try to 'save' the info does it actually say it has been saved?
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Old 27th Feb 2017, 1:04 pm   #24
lightfoot
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Default Re: Help required to repair vintage computer. FIC 486 G10 VT2.

Good morning Kellys eye, I have now followed your instructions and have come up with the following :
Number 1 large diode measuring it left to right (+ to -) reading on diode 377, number 2 smaller diode again as before (+to-) reading on diode 659. measuring from + terminal of coin battery to RTC pin 24 with multimeter set at 2000m with power off reads 16 at 200m 18.9 at 20v .02. with multimeter with power on at 20v reads 3.24v don't know if these reading are any good for you to pinpoint the fault ...me I'm lost the diodes appear to work correctly one way, but the readings mean nothing to me same with the RTC. I trust that you can make sense of it as you are my only hope in getting this sorted.
I would like to thank you again with you patience with me you have been great.
pps.replacements for any parts are not to hand also what kind of values if required are also not known. !?
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Old 27th Feb 2017, 6:38 pm   #25
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Default Re: Help required to repair vintage computer. FIC 486 G10 VT2.

amendment to the last message that is where the reading taken by the multimeter at 20v on it was taken from the - (negative) on the motherboard which showed 3.24v on p[n 24 on the RTC this is the same when running the motherboard with power, therefore the battery is supplying to the RTC but somehow not in circuit to the setup utility hope this will help in analysing the fault, as mentioned before when running with mains power and in he cmos setup utility the clock is running which to me means that the RTC and the crystal are working as they should.
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Old 27th Feb 2017, 8:41 pm   #26
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Default Re: Help required to repair vintage computer. FIC 486 G10 VT2.

chearfulcharlie in answer to your question about whether it says it has been saved, box out askes save y or no answer y cmos setup closes and pc reboots then if you go back into the setup it still remains the same as it was before,
Kelly eye... removed the lable that you mentioned earlier, I removed and this is the result : TMS JL 27C512-15 BLU89418316 THAILAND.
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Old 27th Feb 2017, 9:24 pm   #27
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Default Re: Help required to repair vintage computer. FIC 486 G10 VT2.

OK, your BIOS is in a standard CMOS EPROM memory device (generic 27C512 type) which means the BIOS settings (such as clock, HDD type etc) are backed up to the spare RAM in the RTC chip which itself retains the data during power-down via the coin-cell battery and the steering diodes.

I need a close up hi-res pic of the battery and RTC chip area to confirm any suspicions I have but there is a tantalum capacitor in the vicinity that may be the source of the problem. I cannot be any more specific without inspecting the board.

The fact that Vbat doesn't seem to change value when switching the system power on/off is also perplexing - it should be around 4.4V when running on mains power, falling to 3V with the power off.

Please do what you can to upload (or email me) a picture of the board (around the battery/RTC and BIOS chip) - clarity/focus is essential though!
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Old 28th Feb 2017, 10:27 am   #28
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Default Re: Help required to repair vintage computer. FIC 486 G10 VT2.

Thanks for the follow up and now feeling that we may solve this, but with regard to the 3rd sentence regarding the vbat I have made a mistake when testing this and have confused you as a result, the voltage at pin 24 with power off is as I stated 3.24 but the error I made was the test with the coin battery removed and the powered on in this test the voltage at pin 24 is 0v "is this the fault?" if this is so I don't have this skill to remove the RTC and replace it as the solder areas are too small for me if this is the case, I will try and photograph the area in question and get back to you when ready.
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Old 28th Feb 2017, 11:41 am   #29
lightfoot
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Default Re: Help required to repair vintage computer. FIC 486 G10 VT2.

Kellys eye have sent a private message with the requested hi-res photo which resides in my album, hope I have do this the right way as I've not had to place attachments before. lightfoot.
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Old 1st Mar 2017, 7:23 pm   #30
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Default Re: Help required to repair vintage computer. FIC 486 G10 VT2.

Have sent an email to you with the requested hi-res photo, after the non receipt from my album will have to try that again as I think I made a mistake as I inserted It twice and perhaps you tried both listings...hopefully can come to a conclusion, I've tried to find a circuit diagram of the cmos but had to give up as I was getting nowhere as a summery we have two diodes 6 resistors in the first bank then a further 2 across from the external battery pin ups a transistor followed by small capacitors and the one silver looking capacitor with a marking KDS40 before you get to the RTC, will await for your help.

Last edited by lightfoot; 1st Mar 2017 at 7:25 pm. Reason: spelling mistake
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Old 2nd Mar 2017, 10:14 am   #31
lightfoot
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Default Re: Help required to repair vintage computer. FIC 486 G10 VT2.

Kellys eye , have resent the requested photo today just in case you have not received it or that it's gone into your spam box and you haven't noticed.
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Old 2nd Mar 2017, 6:24 pm   #32
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Default Re: Help required to repair vintage computer. FIC 486 G10 VT2.

Hi, I got the photo thanks.

Unfortunately it doesn't reveal anything I can point a finger at.

So, back to basics! Referring to the datasheet for the RTC chip, it advises that the user refers to the DS12887 device for details of the major factors determining its operation and, when you do so, it is very specific about the supply voltage being above 4.25V else the 'write' function cannot be implemented.

So - checking the DS12885 at pin 28 (Vcc) ensure it is as close to 5V as possible. Many older motherboards suffer voltage problems due to failing capacitors and this is the most likely cause of potential failure to retain data - most of the rest of the board won't notice a degeneration in the 5V logic supply so will operate 'normally' as far as you're concerned but the RTC device uses the 4.25V level to detect a potential power-down situation and shuts off any 'write' process thereby denying the potential to save BIOS settings.

Since Vbat (pin 24) is satisfactory we can stop looking in that area for problems.

The only other potential problem area would be the RCLR pin (RAM clear, pin 25) which is normally pulled high by an internal pull-up resistor so should measure 5V during normal operation. This pin is normally 'unconnected' leaving the reset pin high and shorted to ground by moving the shorting link to deliberately clear the RAM (BIOS) settings so check there isn't anything maintaining a logic 'low' on this pin.

If you get the right voltages at all points mentioned above then we will have to declare the RTC device as defective and look to replace it.
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Old 3rd Mar 2017, 10:10 am   #33
lightfoot
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Default Re: Help required to repair vintage computer. FIC 486 G10 VT2.

Thanks for getting back to , as you said that the voltage on Vbat pin 24 is ok! I have check the voltages randomly prior to your last messages but now you have given me direction I will check and get back to you with the outcome on checking the Vcc pin 28 and also RCLR pin 25. one thing keeps nagging me is in the past with all FIC motherboards and others 486's that when you reset the bios in bios setup utility as well as setting the time and date you have to (already mentioned previously) enter the hard drive perimeters, on starting the setup utility on bootup on this motherboard the perimeters for the first drive is entered automatically which would never happen on a 486 and only this drive (the first) is recognised, I'm wondering if the bios has been corrupted when it was flashed with that HP4.BIN that was on the sticker and that's the reason why it acts this way ie not able to save as it's fixed if so can this EPROM bios chip be flashed on the motherboard as I've done in the past or will it need to be done using an EEPROM copier.
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Old 3rd Mar 2017, 12:57 pm   #34
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Default Re: Help required to repair vintage computer. FIC 486 G10 VT2.

Most EPROM programming uses CRC as error correction when programming - but I'm only assuming 'most' - not all. For there to be an error it would mean deliberate disregard for any error message generated in the programming procedure and given how simple it is to RE-program a device I wonder at the methodology of allowing such an error to be carried through?

Of course such an error would potentially do as you state as far as the BIOS settings are concerned and re-flashing the device is a simple method to alleviate any potential problems in that direction however given the age of the board I would still be checking - potentially replacing as a matter of course - the capacitors associated with on-board smoothing and their associated risk to the required logic levels.

Either way I hope you keep the thread informed of progress as such information is always beneficial to the collective knowledge when it comes to faults as you have encountered.
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Old 3rd Mar 2017, 4:19 pm   #35
lightfoot
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Default Re: Help required to repair vintage computer. FIC 486 G10 VT2.

Hello Kellys Eye, sorry I'm late getting back to you with the readings I can now do this and they are on Vcc pin 28 it is 5.2v and on RCLR pin 25 it's 3,66 not the 5v you mentioned the pin 25 is soldered to the board, can you tell me how I can check further (unconnected) mentioned. Can you confirm that yes I can re-flash the bios as your answer left me unsure, as I have already paid an amount already for this board I'm hoping that with your help we can solve this as this board is of the spec is required to use the cards (daugtherboards) and software on the hard drives from the previous motherboard as the difficulty of finding another board and incurring the same or extra cost, I'm prepared for some cost if we can just get this fixed.
Am I reading this right that you cannot help further as I felt that we were near finding a conclusion and really appreciate the help you have given so far and a conclusion will be helpful to every who reads this thread in the future.

Last edited by lightfoot; 3rd Mar 2017 at 4:23 pm. Reason: additions
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Old 3rd Mar 2017, 8:55 pm   #36
kellys_eye
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Default Re: Help required to repair vintage computer. FIC 486 G10 VT2.

Any further tests/checks would involve the use of data bus analysis equipment and, with the possibility of device replacement (RTC), the appropriate hot air rework tools (or some delicate chop'n'solder techniques).
Much as I'd like to progress this on a hands-on basis I no longer use such equipment so cannot help.

As you infer, fitting a replacement BIOS chip is the easiest route if such equipment/techniques aren't available and we have to take the most appropriate route with what we have at hand.

The only other potentially successful path would require a full schematic of the board - these are very hard to come by but perhaps there is a forum dedicated to these obsolete motherboards that can assist in greater detail or with replacement parts - I certainly seem to be able to find 'any' forum I've had a passing interest for!
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Old 4th Mar 2017, 11:36 am   #37
lightfoot
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Default Re: Help required to repair vintage computer. FIC 486 G10 VT2.

Thanks for coming back to me as you are electronically proficient than I am as i just get by with small things and this is technically a bit to much, as the reading on pin 25 RCLR is 3.66v and the reading on pin 24 Vbat is 3.24v could it be that as the voltage is higher on pin 25 that this causes the alterations in the setup utility to be lost at the new boot up just the same as a battery that has run down.
thought that maybe you could remove & replace the RTC for me chop'n & solder (see private message) with this changed maybe the problem would be solved then afterwards the bios could be flashed as doing it before could mean me losing the one hard drive I currently have.
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Old 4th Mar 2017, 12:11 pm   #38
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Default Re: Help required to repair vintage computer. FIC 486 G10 VT2.

Just thinking outside the box -
but have you tried running the board without any hardware attachments (floppy.HD cards etc) ?

What do you need this computer to do? - as someone might be able to suggest a piggy back that enslaves the original board.
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Old 4th Mar 2017, 1:58 pm   #39
lightfoot
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Default Re: Help required to repair vintage computer. FIC 486 G10 VT2.

Yes i have it it boots to the graphic card then memory count then I press del to enter setup, hard drive on this bootup is zero'ed as expected, entry of date & time on reboot are still on default..cmos not held...as for what I what this computer for was explained at the beginning of this tread however I'll explain again that this was until the last fic board failed used as a server running win 3.11 with printers and scanner needless to say I wish if possible to maintain this because of the software & hard drives. Oing back to the hard drive with the current problem motherboard when attached the setup utility is installed with all the parameters it acts as if the setup utility is using the iDE HDD auto detection that's part of setup. the size of any hard drive is auto detected up to 528MB.

Last edited by lightfoot; 4th Mar 2017 at 2:01 pm. Reason: addition to thread
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Old 9th Mar 2017, 4:32 pm   #40
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Default Re: Help required to repair vintage computer. FIC 486 G10 VT2.

Have you considered migrating the applications to new hardware?

If you dont then the next thing to die might be your hard drive and then you're in a bit of bover?

Presumably if you had backups of the drive you would want to restore to more reliable server hardware anyways?
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