Discussion in 'Retro Gaming and Vintage Computing' started by Duke, 3 Feb 2019.
I use an Ark Logic card in my 486 machine. Pretty good DOS performance
Well I got to testing my 486 motherboard tonight. No activity on post card and seemingly nothing I could fiddle with would change that. After a while I did notice a couple of things.
The CPU was still stone cold but the cache/bios/chip set were all warming. I then tried the voltage regulator and that was also stone cold. So I thought I would try a 5v CPU instead and:
Now I need to hope I can replace this:
It has C3420 written on it. Does anyone know where I can source a replacement?
Looks identical to the one I had to replace on my M919. I’ll dig out the part I replaced it with for you @LewisRaz
EDIT: You can use a BD131 NPN transistor, that’s what I used. Plenty on eBay for a couple of quid, UK stock.
Is this the one? https://www.ebay.co.uk/itm/BD131-Tr...p2349624.m46890.l6249&mkrid=710-127635-2958-0
That would do the trick, yes!
Just picked this AST Pentium desktop up for £25. Will make a nice little project
@cee-S-dee looks good.
My 40 quid PC update:
The LG monitor is good but is dark on the display, even with the brightness up to the max, you struggle to see Doom. Duke3D has a software brightness setting and this works well.
The PC itself is a tidy AMD 2500 with 256 MB RAM. It's in a lovely beige case with 2 HDDs, 2 CD drives and a floppy drive. The motherboard is an NForce2. Inside was remarkably tidy. No dust. Not used as an ashtray. I'm pleased.
@cee-S-dee looks a nice buy that. Great price!
@paradigm I ordered this one in the end as its a half the price https://www.ebay.co.uk/itm/132471960633?hash=item1ed7f1b439:g:798AAOSwO41aRmSY The "BD131"
Also noticed by accident that this motherboard seems happy with my 2 32mb EDO sticks. My last 486 pci motherboard had an absolute fit when I tried to use them. Although I am likely to just use 16mb for the final build.
So long as it’s a BD131 NPN transistor then it’ll be fine. Can’t wait to see you get it fixed
Cheers for your help mate! I must say I am quite confused by all of this tho! I thought transistors increased voltage!!? But this is making a 3.3v from 5v?
I was comparing the datasheets for the C3420 and BD131 and they look quite different but I cant really decipher what means what.
Capacitor and resistor values are so much easier to understand!
Transistors can be used to increase voltage, along with a buck converter circuit, but by switching slower they can also reduce voltage. Imagine a 5v rail that’s only “on” 50% of the time, once smoothed out, the resulting voltage would be roughly 2.5v, this is how switched mode power supplies work.
Ill admit that I’ve not checked the data sheets of the original and the BD131, but I got the recommendation from someone who’d already done the same on VOGONS.
Ah thank you. I have just tested the one in this board and there is continuity between the collector and the base so it is definitely a dead part!
Removed the old one without completely destroying the board
Also found your thread about your one which has helped a lot!
The vias look a bit mangled on the back of the board (or is that flux residue?), just make sure you get a good solder contact on the top side of the board to compensate!
Its just flux residue this time I went mad with the flux as I was worried about repeating what happened to that 386
Haha. Your soldering does look like it’s getting neater! Installing the new transistor is the easy bit so you should be golden now.
I think it helped that I pre heated the entire board with the hairdryer so the soldering iron was not trying to heat up massive chunks of copper traces by itself.
I also used your thread to properly work out the transistor as the pinout online had base in the middle which made my test very wrong. Then I was reading your thread considering looking at the transistor the same way up it is in my pic when in fact the other poster was talking about it as if the pins were coming out of the top. Got there in the end tho and now I think I understand it much better.
Preheating the board does make a noticeable difference, as does using good flux.
So when comparing your pinout to mine, is yours the same?
I’ve just received another M919 that was “faulty”, it too seems to be fine with 5v CPUs, so I need to order a couple of BD131s! Should be a quick fix and flip purchase.
Yes on mine the BASE was the right pin when looking at it from the angle in my photo above. This was a bit confusing as the person on vogons was mentioning it as the left pin, then I realised he was talking about it as looking from the other direction.
Found these, thought they were long gone! Ordered some LR44 batteries to see if they still work
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