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Upgrading IBM 5162 XT/286 to 8 MHz

haglebu

haglebu

Experienced Member
Joined
Nov 22, 2018
Messages
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Location
Germany, Lower-Saxony, Hildesheim
Based on research here in the forum, I upgraded my IBM 5162 XT/286 to 8 MHz as follows:

1. crystal Y1: 12 MHz to 16 MHz
2. BIOS: AMI 1989 / WINBOND W27E257-12
3. RAM 0-512: 15ns to 10 ns
4. RAM 512-640: switched off, as I don't have 10 ns chips; but it will be upgraded.
5. NPU: not yet installed

I only switched ON the converted 5162 for max. 1 minute and tested it with CHECKIT: The frequency changed from 6 to 8 MHz without further action.

Now my question: Are further adjustments necessary for continuous operation?
 
Typically the 6MHz AT boards overclock to 8MHz without much of a fuss, even if you don't change anything.
If you want to play it safe, you can also replace the 82284 clock generator, and 82288 bus controller (the ones installed may already be rated for 8MHz though).

I have also overclocked my XT-286 board, but I have mine running at 10MHz and it seems to handle it pretty well. I replaced the same parts you did, as well as the 82284 and 82288. I also tested at 12MHz, and it seemed to handle it a lot better than the 5170 AT boards I tried...though the AT bus will run at 12MHz, so you need to make sure you expansion cards are up to the job.
 
In my XT/286 the clock generator Siemens SAB 82284P is installed at U79. According to the Siemens manual the SAB 82284P generates a system clock up-to 16 MHz for SAB 80286 Processors.
 
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I don't think I've ever seen 100ns 41256 or 4464 chips... Are you sure you can't use 120ns ones though? Usually expansion boards with 120ns memory will work fine in 8MHz AT's... Although if not, would that be due to the fact that the 5162 is 0 wait state and the 5170 is 1 wait state?
 
Yes, in the range from 512KB to 640KB I have installed memory chips from NEC (D41464C-10), see picture.

IMG_1616.jpg

Probably 120ns chips are also sufficient. According to „minuszerodegrees“ in the motherboard of the 5170 (Type 3, 8MHz), only 150ns RAMs are installed by default. But I didn't have 120ns RAM at hand, so I used 100ns.
 
Addition: According to the users manual of the AST Rampage 286, which was made for the IBM XT/286 and the IBM 5170:

„The RAM chips used with the Rampage 286 board must be 120-nanosecond access time or faster (such as 100-nanosecond).
User's manual, p. 1-3, 1986“

rampage-286.png
 
I would like to share my experience with overclocking the IBM 5162. After replacing the BIOS with a modified one, my unit ran at 8 MHz without any problems. After replacing the RAM with a faster one, I was able to achieve stable operation at 10 MHz. Longer tests, however, showed that at 10MHz the original HDD/FDD controller does not work properly and does not allow the HDD to be formatted. The optimal speed turned out to be 9MHz, at which HDD formatting works properly and the system runs absolutely stably without replacing the RAM with a faster one.
 
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