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Identifying XT clone mainboard

MCbx

Experienced Member
Joined
Jan 27, 2007
Messages
75
Location
Poland, Cracow
Hello
Recently I restored an old XT mainboard, it's a 5160 clone with a bit different ROM selection circuit, and I wonder who made such boards, what for (was there a system?) and when, in my unit components are from 1984-85 (chips are made by TI and Nec). It does not look like a simplified Taiwanese clone. In typical clones, chips were soldered into board and in best cases the only info on silkscreen was type of ROMs.
201810270142041.jpg
In this mainboard, all chips are in sockets, types are printed on silkscreen, component values (including passives and connector types!) and DIP settings are printed too. There is also some breadboard in a corner. Making such board is far from a cheap clone.
The ROM is a modified 08/16/1982 IBM's burned to EPROM (came without sticker, so no info from it). There is a logo behind NPU socket which looks like stylish S with a resistor symbol in it.
201810270142042.jpg
And the male ISA connector on the edge of the board - what is it, is it for some kind of riser?
ROM circuit allows to connect not only ROM, but also to connect /MEMW to some sockets R/W pin like for SRAM. Additionally IRQ2 can be connected to ROM socket pin 2 (usually A12). Was there a configuration involving RAM in ROM area?
Thanks in advance
 

T-R-A

Veteran Member
Joined
May 17, 2009
Messages
524
Location
Western NC
And the male ISA connector on the edge of the board - what is it, is it for some kind of riser?

Likely a "diagnostics port" used only in production/test of the motherboard. It's a common practice in several PCB's.
 

MCbx

Experienced Member
Joined
Jan 27, 2007
Messages
75
Location
Poland, Cracow
Thanks for reply!
It is certainly ISA expansion as it has all signals for it, tested it with ohmmeter.
I got some more information and there indeed was such option to connect SRAM in ROM area, but it was not compatible with anything except some specialized software.
 

MCbx

Experienced Member
Joined
Jan 27, 2007
Messages
75
Location
Poland, Cracow
That's it! And I also have a IBM BIOS copy. My unit has holes for reset button, but no button soldered in, only reset jumper which is not present in another unit. There is also no logo, so it may be an early one, late one or clone, but it's generally this design.
Knowing the name I found a nice assembly information in a PC Mag article.
Thank You for this information!.
 

Hebowyr

New Member
Joined
Oct 4, 2018
Messages
9
Location
VA, USA
Very similar in shape and design to my 8088 board in a "wedge technology" clone. Only difference is the chip manufacturer being a mix of AMD, Intel, and Mitsubishi rather than NEC,
 
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