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Agent Orange
June 23rd, 2014, 05:04 PM
While playing with one of my 286 machines a short while ago C7 (tantalum) on my VTI-XTB VER 2.0 controller left our world. I can't believe such a little guy could put out so much stink and smoke. I'm wondering if anyone might have this board in their collection and if so, could provide me with the value of C7. Thanks in advance for looking.

Mikorians
June 24th, 2014, 06:31 PM
DO NOT blame me for this, but many TINY capacitors are filter capacitors (esp. from that era and earlier)
If it's at the head of a socket, check adjacent sockets.
Most TINY caps are for hi-freq noise and CAN be somewhat range tolerant.
And (once again, don't blame me) common values are selected to save cost.
I'd try a .1uf cap if it isn't polarized (no +/- sign)
The only other common filter cap size I can think of is .1pf (does almost nothing)
This is all I can offer you (from distant, foggy memory)
All this-- IF the card still functions.
If it is dead, you might have a deeper problem.
I'd ask myself why the cap blew, and I'd be hesitant to ruin a motherboard putting it back in...
So there you are.
Oh and I forgot how many volts DC- the chips require 5VDC.
I don't remember the cap size, I assume 5V also.

-this ancient wisdom applies only to old TTL roach chips (DIP), NOT to anything VLSI (square chips)

Mikorians
June 24th, 2014, 06:48 PM
Also- an aside note- kerpow, huh?
Sounds like quite a current load, the cap may have actually SHORTED and killed what it was attached to.
I'd remove its corpse first if it didn't blow into a million pieces!

But ya know, even if you fix this somehow...

Flaky circuitry doesn't do you any favors...
Don't pass it on to someone else...

Agent Orange
June 24th, 2014, 08:16 PM
Also- an aside note- kerpow, huh?
Sounds like quite a current load, the cap may have actually SHORTED and killed what it was attached to.
I'd remove its corpse first if it didn't blow into a million pieces!

But ya know, even if you fix this somehow...


Flaky circuitry doesn't do you any favors...
Don't pass it on to someone else...


Thanks for your theories and concern. I've been dabbling in electronics for over 50 years now, so I'm not exactly a newbie to the repair game. It's not used as a filter in this application. I've more or less determined that it is part of the controller's activity lamp circuit. I'm probably never going to see a schematic for the thing, so I'll try a 47 MF 25v and see what happens. Fortunately caps are cheap. The nature of a tantalum cap is that they normally short when they go. BTW, I will sell this 8-bit IDE controller board down the road. The reason that the forum's own IDE-XT controller took off was a dire shortage and the absurd prices of the 8-bit IDE controllers at the time (if you could indeed find one). I consider this card and others like it to be in very short supply and the demand is relatively high.

Late edit: The cap is definitely 10v 10uf (wife's eagle eyes) :thumbsup:

mikey99
June 25th, 2014, 05:57 AM
I found some discussion about this same card with some pictures in an older forum post:

http://www.vintage-computer.com/vcforum/showthread.php?15819-VTI-XTB-IDE-card

Agent Orange
June 25th, 2014, 07:22 AM
I found some discussion about this same card with some pictures in an older forum post:

http://www.vintage-computer.com/vcforum/showthread.php?15819-VTI-XTB-IDE-card

Thanks for that Mikey. I saw that post when I did a search. Hopefully, I'll have the controller up and running in a day or so. BTW, its tied to a Miniscribe 8450 40MB.

mikey99
June 25th, 2014, 11:18 AM
Looking at the pictures of the card from the other thread, capacitor C8 looks physically the same size.
I would say there is a very good chance its the same value as C7.

Agent Orange
June 25th, 2014, 01:06 PM
Looking at the pictures of the card from the other thread, capacitor C8 looks physically the same size.
I would say there is a very good chance its the same value as C7.

You are correct. They're both 10v 10uf. There was just enough left on the popped cap where you could make out 10uf (not my eyes, hers). Just got back from the only local electronics supply outlet on my side of town and the dang place was padlocked. So, I'll have to go through all my stuff tonight and see what I've got. Failing that, I'll go to JAMECO.

mikey99
June 25th, 2014, 01:52 PM
I've used an electrolytic as a replacement for a tantalum a few times and it seemed to work okay.
Tantalum caps are hard to find and somewhat expensive. ebay seems to be the best place to
obtain tantalum caps lately.

Agent Orange
June 25th, 2014, 02:29 PM
I've used an electrolytic as a replacement for a tantalum a few times and it seemed to work okay.
Tantalum caps are hard to find and somewhat expensive. ebay seems to be the best place to
obtain tantalum caps lately.

Just ordered a pack of 10 ea. 25v 10uf tantalum's from JAMECO for $11.37 delivered. Heck of lot easier than pawing though all my stuff looking for the little buggers. I'd really like to get this thing up running in a week or so because I plan to sell it. There will be a large 'hew and cry' when I list it. There are those on this forum who think that its outrageous to ask the going price for vintage gear. Since I'm not a dealer/retailer and just an occasional seller, it really doesn't bother me. Assuming the controller comes up as expected, I plan to offer it with a working 8450 Miniscribe and cables.