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Legit Harris 25MHz?

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Reply 20 of 24, by kool kitty89

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I just got 4 of these and all appear to be DOA. I'll deal with the seller/ebay, etc (and probably double-check them in the process).

Tried at 8 (de-turbo) 20 and 25 MHz on my no-name variant of a PCChips M-205 (with Citygate D60 chipset AKA Hedaka D60, CG logo might be fake on mine, but PCChips used CG chipsets earlier on, and there's no 205 mark on my board, even, so might be vanilla markings).

I installed a socket for the oscillator and swapped in a 50 MHz one for the test. The original 20 MHz Harris CPU posts and seems to work fine (no disk drive hooked up currently) at 25 MHz with 60 ns CMOS DRAM installed, though. (I let it run warm for a while, too, and it still posted again; granted these CMOS Harris 286s seem to run fairly cool at high clock speeds ... not like an NMOS Intel 286-12 I nearly burned myself on)

Anyway, since Tiido and some others seem to have gotten working examples, maybe I just got a bad batch. OTOH, if they're remarked, they're also not ideal for what I had planned: trying to push the limits of the D60 chipset (and maybe some others I can get my hands on) beyond 25 MHz, or at least no better than randomly selected original 20 MHz parts would.

Also, most (or all?) real Harris 286 20s aren't engraved, but use white print on a satin/smooth surface finish, not the rough/stippled texture on these. The print is also somewhat larger and covers more of the surface.

Like these 20 MHz ones (apparently from the late 90s)

I'm tempted to try some of these other ones.

Harris part number and looks like the print style and finish of real ones, but missing the Harris logo and name. And from 1991, so long before the 1999 Intersil spinoff company was created, but maybe some were marked like that.

Last edited by Stiletto on 2020-03-02, 05:24. Edited 1 time in total.

Reply 21 of 24, by maxtherabbit

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I'm now convinced the chips in the OP are fake. I ended up grabbing a legit 20MHz part

Last edited by Stiletto on 2020-03-02, 05:23. Edited 1 time in total.

Reply 22 of 24, by kool kitty89

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Those CPUs don't even get warm if left in for several minutes at 25 MHz (and thankfully didn't damage the board at least), so they might be totally fake plastic packages: PCChips fake cache chip style, or something else weird is going on. (maybe remarked chips other than 80286s that use PLCC-68 packaging, like 186s, 188s, 68000s, etc, that might not even complete a circuit when installed in the correct orientation)

I somewhat doubt they're remarked Intersil-era parts, and I also doubt even those would run too cool to notice above ambient temps, at least at 5v and 20-25 MHz. (at 8-12 MHz, my Harris 20 MHz chip is almost cold, though)

At least that original CPU seems to run at 25 MHz (and the board itself does), and now I know the board is almost certainly 1990 vintage, going by the date code. (ie if N9050 means 1990, week 50, that would be December of 1990, or August of 1990 if it corresponds to the US Fiscal calendar)

The BIOS posts with a 1990 date, too. (AMI BIOS, Triple D Development Ltd)

Also

maxtherabbit wrote on 2020-02-23, 15:15:

I'm now convinced the chips in the OP are fake. I ended up grabbing a legit 20MHz part

I actually just went for the 5x offer discount there, mostly in hopes of getting at least one that does better than 25 MHz. (or maybe just 25 MHz if my current one turns out to not be stable)

I'm also going to test the waters with that other 25 MHz listing without the Harris branding.

I know there's actual Intersil 25 MHz parts on ebay too, but they're a good deal more expensive and the benefit of domestic US shipping time isn't a deal-maker for me either. (I might try one at some point if my board seems like it wants to do 30 MHz; I don't think I've seen a working 286 system mentioned above 28 MHz before)

Also note, this board (and I think all the PC-Chips style boards, both this chipset and the later Toshiba one used in the M216/219) doesn't appear to have any wait state adjustment, so it's probably fixed at the IBM style 1 wait state configuration (also probably why it came with 80 ns RAM), so higher clock speeds is the only direction to go for added performance. (I know zero wait state 20 MHz boards usually beat 25 MHz 1-wait-state ones in memory-bound tasks too, but for games and benchmarks that are slow-instruction-heavy and register-register activity heavy, the clock speed should be a win)

Now that I know X-Wing (1993 FD version) actually runs on a 286, that's going to be high on my benchmark list. I'm also going to bet it relies more (or entirely) on multiply/divide instructions for its 3D math and not look-up-table enhancements/tricks like Wolfenstein 3D does. (Wolf3D also makes heavy use of arbitrary shifts, which is one of the reasons it can't run on an 8088 unaltered ... not sure about 186/V30 given those include the added instructions)

Wing Commander is probably a good one to use, too, but I know it's finicky about EMS implementations being strictly 100% MS/Intel/Lotus compliant. (I know the Headland scheme is, but not sure about the D60 ... albeit WC can work fine in just 640k if DOS isn't eating too much of it)

X-Wing also runs in plain MCGA/VGA 13h screen mode vs unchained mode that Wolf3D uses, but I'm not sure how wait states impact that.

Last edited by Stiletto on 2020-03-02, 05:23. Edited 1 time in total.

Reply 23 of 24, by kool kitty89

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No problem getting a refund from the seller. They also mentioned checking with their supplier.

I'll hang on to these, but as far as I can tell they're totally dead and/or not even 286s.

Reply 24 of 24, by kool kitty89

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I realized the 286 board I was testing them in only has a 1/2 divider for the de-turbo mode, so I was trying those duds at 10 or 12.5 MHz (forget what oscillator I was using at the time, probably 50 MHz), so they might still work at 8 MHz. I'll try that at some point, but given they didn't get warm at all, that doesn't seem to be the likely cause. (maybe they're 286s that got resurfaced and a corner was re-cut in the wrong place, so I've been plugging them in the wrong orientation: I've done that once with a real 286 and it stayed cold and didn't seem harmed, but it might depend on just what wrong-way it's inserted)

The fake date code on there also seems possible to be the date they were resurfaced as Chinese remarked chips tend to have that done for some reason (date of 'remanufacture' rather than a plausible counterfeit date).

These appear to have had the original printed markings scrubbed and the surface etched or retextured (sand blasted maybe) and then engraved with a reasonably convincing Harris logo and markings. If Harris actually used engraving, it'd be more convincing, but the technique avoids the simple tests and signs of other remarking methods and obviously won't be affected by acetone or any solvent short of something that can dissolve epoxy resin.

I'm not sure if acetone will take off the original (real) print, but I don't want to try and ruin one of my good ones.

The original 1990 marked 286-20 that came in my M205 seems to be a pretty good overclocker in itself, which is kind of neat. (though tinkering some more and trying 54 MHz oscillators points to the board tolerating 27 MHz, but the CPU not doing so when even moderately warm, and these plastic casings don't have good enough thermal properties to solve that with cooling, I think ... maybe with a thermoelectric cooler stuck directly to it for sub-ambient cooling, but then there's condensation issues)

Heatsinks and/or fans are probably more useful for keeping hot-running NMOS 286s stable (and industrial 286 boards tend to have little sheet metal heatsinks on them). Back when 286-12s were the fastest grade available, that was probably relevant, though soldered-on NMOS 286-16s (and people unwilling to buy another CPU) would be too. A Siemens 286-16 I tried seemed to go OK at 20 MHz until it warmed up to the too-hot-to-touch range, so a little heatsink or good airflow would probably do a lot for that. (and I've seen at least one very late generation 286 board with an NMOS Siemens 286-16 soldered onto it, definitely one oddball PC_Chips looking 'SARC' marked chipset one, but I think a Headland HT12 one as well)