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Newly aquired Tandy 6000HD! Lots of questions to follow...

Chromedome45 said:
well found a short near one of the PALS. Seems like the 12 ohm reading is normal. Still getting bughlt no68k even after swapping the CPU. Reseating all socketed chips. Cleaned edge connector etc. So no one out there has seen this problem before. Please help I really need it on this one.
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Check for a shorted capacitor, possibly one or both of the electrolytics (C54 and C55, both 100 microfarads 16V). These might possibly be tantalum caps, in which case those are known to short out in this age range. Typically they'll show some physical fault, though. The PALs being U6, U36, U40, and U48: three of those are near C54 and C55.

Also, while it would be rare for them to fail shorted, it could possibly be one of the 0.1uF bypass caps scattered all over the board. But I'd start with the two electrolytics.
 
::Lowen. Check for a shorted capacitor, possibly one or both of the electrolytics (C54 and C55, both 100 microfarads 16V I did check these they are good. Also how would I check the PALS? I do not have an O'scope all's I can do is look for shorts on the pins which I doubt would be there.

I will have a look at the bypass caps.
 
Ok now I am confused once more. I thought the 256/1 Meg memory board required 128 cycle refresh RAM? Well what is in there and how I got it was with NEC 41256 chips which are 256 Cycle! But it did work with that RAM in it. So what does it actually require? the Service Manual says the Refresh circuit in the 1 - 2 jumper position generates 128 Cycle. :confused:
 
Chromedome45 said:
Well according to Modem 7's page on 256k RAM chips looks like all of them are 256 cycle. Hmm
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That board can handle either 64K chips or 256K chips, and the jumper is for 128 cycle refresh on the 64K chips. As far as I know there are no 128 cycle 256K RAMs. If it worked at any time then it means the board works with those chips, and you should leave the jumper where it was when you started, since it worked (it just simply would not have worked at all ever if it was set to 128 cycle).
 
Chromedome45 said:
:... Also how would I check the PALS? I do not have an O'scope all's I can do is look for shorts on the pins which I doubt would be there. .
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Pull each socketed chip one at a time in turn until the short goes away (or until you've pulled all of them and it doesn't go away, at which point you have a choice as to whether you want to tackle a repair attempt or not without a scope or a logic analyzer). A dead short will generate a good deal of heat, so check for a really hot chip or other component.
 
Ok back to the 68k Board. I really am at a loss as to why it acting like it is. 98% of the time I try to boot Xenix and I get the bughlt no68k but on occasion I will attempt to boot then it throws a kernel panic. So even when it try's to work it doesn't really.

Anyone have a spare 68k board? Short version? Or the PAL chips that go to this board. Maybe one of them is going bad.
 
See page 16 of the 6000 service manual. 68k board should be in the top slot, followed by memory board(s), then video/keyboard, then graphics (if present), then multi-terminal interface, then hard drive, and finally Arcnet (if present). It isn't quite clear about whether cards should be top-justified and/or bottom-justified when there are open slots.
 
I finally bothered to take the top cover off of my Model 6000. Boy, is it dusty in there! Extricating the power supply to check for incendiary Rifa caps is going to be a chore. I seem to recall that it was a chore in my Model 12, and it didn't even have a card cage in the way.
 
Chromedome45 said:
On the 6000 does it matter if the memory board is above or below the 68K CPU board??
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Memory board goes below 68 k board. I don't think its physically possible to put the memory above the cpu board with the standard 68k cables.
 
Pete: Oh it can go on top. That's the way mine is set up.

Have a look at the notejump for the 6000. It says CPU then memory in top 2 slots from bottom to top. So there is my confusion point.

Mark: remove 2 small screws at the front of the power supply lid they are sitting in a slot just loosen them.
On the top edge behind the fan is a black #6 screw and to the left side of that cover is another one remove them. This will enable you to see the power supply board and have a look at the Rifa's. Mine were cracked so I took a pair of needle nose pliers and just broke them by twisting. And then removed the left over chunks. So my 6000 actually is missing the rifa's I am using a surge protector so I think they are not needed. But that is me. You may do what you think is right.
 
Thanks for the pointer! I'll replace mine with new non-paper-dielectric safety-rated caps. I'm a ham radio operator, so EMI is important to me. So, my supply will be coming all the way out if the expected Rifa caps are present.
 
Cool I wish you luck. Oh there are 5 or more of them in there I think. Yeah one day I will get the needed Rifa's and replace them. I just wanted them out quick for testing purposes. Also they are in the little Model III power supply that is powering the HD drive. And EMI is not welcome when around Ham radio gear!

And as you stated Memory than CPU according to the service manual. Will try that. Thanks for the pointer.
 
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NF6X said:
See page 16 of the 6000 service manual. 68k board should be in the top slot, followed by memory board(s), then video/keyboard, then graphics (if present), then multi-terminal interface, then hard drive, and finally Arcnet (if present). It isn't quite clear about whether cards should be top-justified and/or bottom-justified when there are open slots.
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The only spaces should be between the last Z80 card and the first 68K card. The Z80 cards are supposed to go in a very specific order, since the card order sets the IRQ priority in the Mode 2 interrupt daisy chain. Also, there must not be any spaces between any Z80 boards that are part of the IRQ chain, since the IRQ continuity is maintained by the cards themselves. Hans01 has dealt with this on his board for the lo-tech IDE interface, and perhaps he might comment.
 
Oh I am well aware of what EMI can do. Try chasing down interference with a radio near an HF listening post! I will put the caps back in it was just for testing purposes as mentioned to see if this 6000 would power up.

Anyway back to the subject may have found an anomaly with my 68k board. U3 and U50 are supposed to be MCM3482 latches according to the service manual. In U3 is a 74F373 and in U50 is a MCM3482. Looking at NF6X pictures his U3 is also a 74F373 but his U50 is a 74AS533. So my question is which chip is the most compatible with the MCM3482? and could this be causing my problems I am having with Xenix?
 
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Do you know what revision CPU board you have? The 6000 tech bulletins have a boat load of reliability mods for earlier 6000 68k boards.
 
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