VOGONS


First post, by jarcher1701

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Hello. Hoping some knowledgeable folk might be able to help.

I purchased a 386/486 combi motherboard on eBay along with a ATX to AT power supply adapter. I'd powered it on previously, hooked up via VGA to my 1080p monitor, and I just got a black screen. The 486 DX CPU was powering/heating up, along with other components. I tried again today with a different VGA cable and this time, after leaving it a while, a tantalum capacitor blew up (my eyes were a safe distance away thankfully).

I'm using a 10 year old (approx) ATX 250W power supply. I haven't — although probably should have — tested with a mustimeter first.

I have a Cirrus Logic GD5428 in the VLB slot. I bought it untested, so it could be the issue, but it looks absolutely fine.

I have a PS/2 keyboard (with adapter) connected. Before the capacitor blew, the keyboard was being powered and I was able to enable and disable num lock.

Photos are below of the board and blown cap. Any advice regarding the black screen and next steps regarding the blown cap? Many thanks in advance.

https://photos.app.goo.gl/wS9HopHL74Pw8uEw5

Edit - I also removed the battery. It had leaked slightly, with only minor green corrosion nearby which mostly came off. No damage to tracks. Would a lack of battery result in a black screen? I'm doubtful.

Last edited by jarcher1701 on 2022-08-16, 08:04. Edited 1 time in total.

Reply 1 of 16, by TrashPanda

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Tantalums throw tantrums ...I hope it didn't take other stuff with it when it went, angry pixies take no prisoners.

Oh noes, the cap let the shmooo out 😁

Reply 2 of 16, by kixs

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Replace the cap.

Always use tested parts so you only have one unknown. Now you had two - VGA card and motherboard.

If the num lock worked, then the VGA card has some issues. Probably needs a good clean of the contacts. But first solve the cap.

Requests also possible

Reply 3 of 16, by mkarcher

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jarcher1701 wrote on 2022-08-16, 07:55:
[..,] a tantalum capacitor blew up (my eyes were a safe distance away thankfully). […]
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[..,] a tantalum capacitor blew up (my eyes were a safe distance away thankfully).

I'm using a 10 year old (approx) ATX 250W power supply. I haven't — although probably should have — tested with a mustimeter first.

I have a Cirrus Logic GD5428 in the VLB slot. I bought it untested, so it could be the issue, but it looks absolutely fine.

I have a PS/2 keyboard (with adapter) connected. Before the capacitor blew, the keyboard was being powered and I was able to enable and disable num lock.

Photos are below of the board and blown cap. Any advice regarding the black screen and next steps regarding the blown cap? Many thanks in advance.

Remove the remaining pieces of the cap. The cap is just a "power supply stabiliation cap", and the computer will most likely work without it, but being slightly less tolerant to ripple or marginal contacts at the AT power connector. Replace it in the long run. If you can't find the value of that cap, use a 10µF cap with a voltage rating of 10 or 16V if it is connected to 5V or -5V, or a voltage rating of 16V or 25V if it is connectected to 12V or -12V. The higher voltage rating provides more margin before the replacement cap will explode.

I don't expect your power supply to be the real cause of the blown cap, because most supplies have an integrated "emergency shutdown" if any output voltage rises too high. Old tantalum caps often fail all by themself, so there need not be a different failure that made this cap explode. I had all tantalum caps on +12V and -12V on a Compaq server mainboard blow up one after the other when I started using a machine that was in storage for 20 years. The power supply in that machine is fine.

Being able to toggle NumLock proves the mainboard to be very likely good. I recommend you to try with a proven ISA VGA card first, as corroded VL contacts (as already mentioned in this thread) are oftentimes causing VGA issues on old 486 mainboards.

Reply 4 of 16, by jarcher1701

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mkarcher wrote on 2022-08-16, 11:25:

Being able to toggle NumLock proves the mainboard to be very likely good. I recommend you to try with a proven ISA VGA card first, as corroded VL contacts (as already mentioned in this thread) are oftentimes causing VGA issues on old 486 mainboards.

Thanks kixs and mkarcher.

I will be sure to replace the cap. Thanks for the advice.

I don't have another ISA VGA card lying around, so I suppose my only option is to purchase a cheap 'working' one from eBay.

I have included a photo of my current card. It was purchased untested, but a visual inspection suggests everything looks okay including the edge connector contacts that look very good. You're right though; this needs to be eliminated as the problem.

https://photos.app.goo.gl/wS9HopHL74Pw8uEw5

Reply 5 of 16, by mkarcher

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jarcher1701 wrote on 2022-08-17, 07:50:

I don't have another ISA VGA card lying around, so I suppose my only option is to purchase a cheap 'working' one from eBay.

Currently, I feel like there are no real "cheap" working graphics cards on ebay. I remember times where you could pick cards based on a TVGA8900B or a OAK OTI-067 chip for nearly free from a heap of "trash", and now they are often sold above 30$/30€. Don't use these model numbers as recommendations to buy. These cards were already known back in the day to be bottom of the barrel, but good enough to produce a picture if performance doesn't really matter.

Your card looks OK to me, too. My experience with VL is that contact issues are common, especially on old boards. Before you invest a serious money into a low-end ISA graphics card, try replugging the Cirrus card multiple times. Try the other VL slot. Try powering the board with the card lifted out of the VL slot by a couple of millimeters (a tenth of a inch). That's basically the standard procedure I do with systems with misbehaving VL video systems. If you happen to have anti-corrosive contact cleaner spray, you might want to spray it into the VL slot.

Reply 6 of 16, by jarcher1701

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mkarcher wrote on 2022-08-17, 08:30:

Currently, I feel like there are no real "cheap" working graphics cards on ebay.

Yes, a quick check suggests the cheapest is £30 GBP for a non-VLB card. And they all seem to be the same seller.

Thanks for your advice. I'll do what I can to test the current card before buying a new one.

Reply 7 of 16, by jarcher1701

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mkarcher wrote on 2022-08-16, 11:25:

If you can't find the value of that cap, use a 10µF cap with a voltage rating of 10 or 16V if it is connected to 5V or -5V, or a voltage rating of 16V or 25V if it is connectected to 12V or -12V. The higher voltage rating provides more margin before the replacement cap will explode.

The blow cap looks the same as two nearby, and they read '4μ7 followed by 16'. I take it that this means 4.7 µ farads and the 16 refers to the max 16v voltage rating. I found some replacements and they've been ordered. Thanks!

Reply 8 of 16, by mkarcher

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jarcher1701 wrote on 2022-08-17, 19:05:
mkarcher wrote on 2022-08-17, 08:30:

Currently, I feel like there are no real "cheap" working graphics cards on ebay.

Yes, a quick check suggests the cheapest is £30 GBP for a non-VLB card. And they all seem to be the same seller.

Based on your currency, I checked ebay UK. I saw a realtek ISA graphics card for £20 + shipping. That's neither a great price, nor a great card, but generally good enough as a basic test card and not exceedingly expensive.

The ISA stuff is still cheap compared to the VL graphics cards, though. For example an Advance Logic card (generally considered subpar, IIRC) for £69 "for parts only". Oh come on...

You interpreted the tantalum cap correctly. Your replacement should work perfectly.

Reply 9 of 16, by Thermalwrong

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There's an ACUMOS AVGA 2 up there as well for £30, that's one of the fastest ISA cards there is for games and worth it imo.

ISA graphics cards and VLB graphics cards do come up for sale cheap sometimes but usually as part of a lot these days. Sadly the supply of VLB cards seems to have dried up or people got better at identifying them and started raising prices accordingly.

Reply 10 of 16, by jarcher1701

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Thermalwrong wrote on 2022-08-17, 22:46:

There's an ACUMOS AVGA 2 up there as well for £30, that's one of the fastest ISA cards there is for games and worth it imo.

ISA graphics cards and VLB graphics cards do come up for sale cheap sometimes but usually as part of a lot these days. Sadly the supply of VLB cards seems to have dried up or people got better at identifying them and started raising prices accordingly.

Thank you for this suggestion. I managed to get it for £25. It's listed as 'tested' and I'm tending to believe that as the seller seems to be a reputable retro hardware shop on eBay. Most of the ISA/VLB cards seem to be sold by him/her in the UK.

I have replaced the blown cap, tried the VLB card again and I'm still getting a black screen. The keyboard numlock and caps lock continues to work. I'm going to assume it's the card that's faulty even though it looks pristine. I tried both VLC slots. I'll keep you guys posted. Thanks for your help.

Reply 11 of 16, by evasive

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If you get the motherboard to work, can you please dump the bios for this page:
https://theretroweb.com/motherboards/s/unknown-v3486ef

Would be greatly appreciated.

Reply 12 of 16, by Ydee

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Maybe not help, but it is free: if I can see right, both J11 and J12 jumpers on your VLB are closed. In this thread is stated, that the card did not work with this setting for another member: Help with jumpers on Cirrus Logic VLB card
Try to set them up as they state further in the thread (J11 closed, J12 open or both open work for him) and see if anything changes.

Reply 13 of 16, by jarcher1701

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Ydee wrote on 2022-08-22, 06:35:

Maybe not help, but it is free: if I can see right, both J11 and J12 jumpers on your VLB are closed. In this thread is stated, that the card did not work with this setting for another member: Help with jumpers on Cirrus Logic VLB card
Try to set them up as they state further in the thread (J11 closed, J12 open or both open work for him) and see if anything changes.

I can't thank you enough. You solved the problem and I would never have thought to check the jumpers. I opened both J11 and J12 and the VLB Cirrus Logic 5428 now works fine. Photos of the boot screen and bios are included in the link below.

https://photos.app.goo.gl/wS9HopHL74Pw8uEw5

Quick question about extended memory count in the photos. This shows 7168KB. There are 8 banks. Does that sound right? Or should it be 8*** something?

I also received the ACUMOS AVGA 2 card and this also works fine - so it would seem I have a working 386/486 motherboard.

My question now relates to the best way to get DOS and games installed. I don't really want to purchase an old IDE hard disk or a floppy drive. I'm aware I need an ISA disk controller. I haven't seen many controllers on eBay for a decent price. For the 'drive' I was thinking about an IDE/SD adapter, such as the one below. I also have a 1GB CF card so a CF adapter might be an option if recommended.

https://www.ebay.co.uk/itm/204061837612

Any thoughts on options here?

Thanks again for your help guys.

Reply 14 of 16, by mkarcher

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jarcher1701 wrote on 2022-08-24, 14:29:

Quick question about extended memory count in the photos. This shows 7168KB. There are 8 banks. Does that sound right? Or should it be 8*** something?

8 Banks (with the standard 1MB modules) provide 8192KB of RAM. Depending on configuration, you typcially lose 128, 256 or 348KB of that for shadowing, SMM RAM or just plain unavailability as it occupies the same address space as the classic IBM PC video RAM/BIOS extension/MMIO/BIOS area. So values of 8064, 7936 or 7848 KB of RAM at the memory test are perfectly fine. 7168 is considerably lower (in fact, it is 7 Megabytes) and might indicate that one of the modules in the second bank is bad.

Try swapping the two banks. If you get 3072 insted of around 8192 that time, you know that one of the modules you swapped is bad.

A bank needs to be equipped with 4 identical modules and is 4MB in size. The detection of 3MB in a bank does not necessarily mean: "3 modules good, one module bad", because the modules are kind-of interleaved. A single missing module would cause detection of that bank as being completely absent.

Reply 15 of 16, by Ydee

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jarcher1701 wrote on 2022-08-24, 14:29:

I can't thank you enough. You solved the problem and I would never have thought to check the jumpers. I opened both J11 and J12 and the VLB Cirrus Logic 5428 now works fine.

I'm glad it helped you, but that wasn't me, it was Uncle Google and the vogoner who shared his experiences.

Quick question about extended memory count in the photos. This shows 7168KB. There are 8 banks. Does that sound right? Or should it be 8*** something?

As far as I know, it should be fine. Megabyte is 1024 kilobytes, so 8x1024 is 8192kB. POST shows you 640kB base memory, 7168kB extended memory and there's 384kB left that's probably used for shadowing as mkarcher writes higher up.

My question now relates to the best way to get DOS and games installed. I don't really want to purchase an old IDE hard disk or […]
Show full quote

My question now relates to the best way to get DOS and games installed. I don't really want to purchase an old IDE hard disk or a floppy drive. I'm aware I need an ISA disk controller. I haven't seen many controllers on eBay for a decent price. For the 'drive' I was thinking about an IDE/SD adapter, such as the one below. I also have a 1GB CF card so a CF adapter might be an option if recommended.

https://www.ebay.co.uk/itm/204061837612

Any thoughts on options here?

Thanks again for your help guys.

I'm not advising here, I'm using the old real hard drives:)

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Reply 16 of 16, by mkarcher

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mkarcher wrote on 2022-08-24, 21:44:
jarcher1701 wrote on 2022-08-24, 14:29:

Quick question about extended memory count in the photos. This shows 7168KB. There are 8 banks. Does that sound right? Or should it be 8*** something?

8 Banks (with the standard 1MB modules) provide 8192KB of RAM. Depending on configuration, you typcially lose 128, 256 or 348KB of that for shadowing, SMM RAM or just plain unavailability as it occupies the same address space as the classic IBM PC video RAM/BIOS extension/MMIO/BIOS area. So values of 8064, 7936 or 7848 KB of RAM at the memory test are perfectly fine. 7168 is considerably lower (in fact, it is 7 Megabytes) and might indicate that one of the modules in the second bank is bad.

This is nonsense. I expected you were talking about the final number of the memory test ("XXX KB OK"), which is expected to be 7848, 7936 or 8064. But that's not the case here. Instead you are talking about the "extended memory size" in ths "system configuration summary". 7168KB is perfectly fine at that point, as Ydee explained. You might get some kilobytes extra if your board supports "memory relocation" and you enable it in the chipset configuration setup, but the 128KB you might get extra are usually not that important. Most games that run fast enough on a 386 system work with just 4MB RAM installed, so squeezing the last byte out of 8MB is not important.