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TonyDuell · 24th Jul 2022, 1:44 pm

This is very odd...

The 8088 on the motherboard is strapped so the pinout is 'minimum'. Like that it can't support a coprocessor. So the Coprocessor card, as well as containing the 8087 contains second 8088 strapped in 'maximum' mode and some interface logic. When you fit the coprocessor card it disables most of the signals from the motheboard 8088 but you have to cut jumper W1 on the motherboard to disconnect the ALE line coming from the motherboard processor. And if you later remove the coprocessor you have to re-jumper W1.

Is this machine known to have worked with the coprocessor fitted?

I know they are very hard to get to, but is the motherboard outputting anything on the Hsync, Vsync and the 2 video pins? Aha, there are some video test points on the motherboard located between the row of LEDs and the beeper. According to the manual they are :

TP8 NFB Actve low full bright video
TP7 SGnd Ground
TP6 CSYNC Composite Sync
TP5 NHB Active low half bright video

Note that according to the schematics, CSYNC is generated along with the hsync and vsync signals by one of the ASICs. I guess it would be possible for it to work and one of the latter 2 signals to have failed. But unlikely

24th Jul 2022, 1:44 pm	#15
TonyDuell Dekatron Join Date: Jun 2015 Location: Biggin Hill, London, UK. Posts: 5,208	Re: HP 150 Touchscreen II repair This is very odd... The 8088 on the motherboard is strapped so the pinout is 'minimum'. Like that it can't support a coprocessor. So the Coprocessor card, as well as containing the 8087 contains second 8088 strapped in 'maximum' mode and some interface logic. When you fit the coprocessor card it disables most of the signals from the motheboard 8088 but you have to cut jumper W1 on the motherboard to disconnect the ALE line coming from the motherboard processor. And if you later remove the coprocessor you have to re-jumper W1. Is this machine known to have worked with the coprocessor fitted? I know they are very hard to get to, but is the motherboard outputting anything on the Hsync, Vsync and the 2 video pins? Aha, there are some video test points on the motherboard located between the row of LEDs and the beeper. According to the manual they are : TP8 NFB Actve low full bright video TP7 SGnd Ground TP6 CSYNC Composite Sync TP5 NHB Active low half bright video Note that according to the schematics, CSYNC is generated along with the hsync and vsync signals by one of the ASICs. I guess it would be possible for it to work and one of the latter 2 signals to have failed. But unlikely Last edited by TonyDuell; 24th Jul 2022 at 1:52 pm.