Delta-S Soviet Sinclair Spectrum clone - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

jay_oldstuff · 8th Jan 2016, 3:01 pm

The pics I posted in post 17 are with the scopes ground connected to a good ground point on the computers PCB. the pics I posted in post 18 are with the scopes ground connected to the video ground. I will see if I can dig out my other scope probe and see if it makes any difference.

Jay

dragonser · 8th Jan 2016, 3:12 pm

Hi,
just a thought, probably wrong I hasten to add....
I wonder if none of the pins on the din socket are ground, and they might have used the case of the din plug as the ground ?
I wonder if you checked with a dvm on resistance range to see which pins were connected to the ground point on the computer.
I can't remember which early computer ( cpm based one ? ) I had to make up a lead to go between the monitor and the computer, it did use din plugs, and they did use the shield on the din plugs as a separate ground connection.
regards Peter B

SiriusHardware · 8th Jan 2016, 8:11 pm

It looks to me as though that last batch of measurements was made with the scope input mode set to AC - if not, then with a X10 probe with its compensation setting out of adjustment.

Were the most recent measurements with the probe on X1 and with the scope input mode set to DC? If not, can you try it again that way?

jay_oldstuff · 8th Jan 2016, 10:24 pm

all measurements taken have been with a X1 probe (has no X10 function) and all taken with the scope set to DC.

Jay

jay_oldstuff · 9th Jan 2016, 12:18 am

I cant find my other scope probe at the moment but have tested this one has continuity and although the ground looks good from crock clip to BNC outer the probe itself measures 169 ohm from probe tip to BNC inner. Is this normal? or is my probe goosed and that's why I'm getting the readings I am.

Jay

dragonser · 9th Jan 2016, 11:34 am

Hi, I think the scope probe should work ok with the 169 resistance from probe tip to inner bnc connection.
But I wonder if there might be a broken ground connection on the din socket on the computer itself ? [ or even on the scart cable you made up. there may be more than one ground connection required to different pins on the scart ? ]
nice to see a picture of the computer on youtube !
regards Peter B

8th Jan 2016, 3:01 pm	#21
jay_oldstuff Octode Join Date: Jan 2005 Location: Hyde, Greater Manchester, UK. Posts: 1,074	Re: Delta-S Soviet Sinclair Spectrum clone The pics I posted in post 17 are with the scopes ground connected to a good ground point on the computers PCB. the pics I posted in post 18 are with the scopes ground connected to the video ground. I will see if I can dig out my other scope probe and see if it makes any difference. Jay __________________ The light at the end of the tunnel is probably the headlight of an oncoming train

8th Jan 2016, 3:12 pm	#22
dragonser Heptode Join Date: Aug 2009 Location: Carshalton, Surrey, UK. Posts: 735	Re: Delta-S Soviet Sinclair Spectrum clone Hi, just a thought, probably wrong I hasten to add.... I wonder if none of the pins on the din socket are ground, and they might have used the case of the din plug as the ground ? I wonder if you checked with a dvm on resistance range to see which pins were connected to the ground point on the computer. I can't remember which early computer ( cpm based one ? ) I had to make up a lead to go between the monitor and the computer, it did use din plugs, and they did use the shield on the din plugs as a separate ground connection. regards Peter B

8th Jan 2016, 8:11 pm	#23
SiriusHardware Dekatron Join Date: Aug 2011 Location: Newcastle, Tyne and Wear, UK. Posts: 11,571	Re: Delta-S Soviet Sinclair Spectrum clone It looks to me as though that last batch of measurements was made with the scope input mode set to AC - if not, then with a X10 probe with its compensation setting out of adjustment. Were the most recent measurements with the probe on X1 and with the scope input mode set to DC? If not, can you try it again that way?

8th Jan 2016, 10:24 pm	#24
jay_oldstuff Octode Join Date: Jan 2005 Location: Hyde, Greater Manchester, UK. Posts: 1,074	Re: Delta-S Soviet Sinclair Spectrum clone all measurements taken have been with a X1 probe (has no X10 function) and all taken with the scope set to DC. Jay __________________ The light at the end of the tunnel is probably the headlight of an oncoming train

9th Jan 2016, 12:18 am	#25
jay_oldstuff Octode Join Date: Jan 2005 Location: Hyde, Greater Manchester, UK. Posts: 1,074	Re: Delta-S Soviet Sinclair Spectrum clone I cant find my other scope probe at the moment but have tested this one has continuity and although the ground looks good from crock clip to BNC outer the probe itself measures 169 ohm from probe tip to BNC inner. Is this normal? or is my probe goosed and that's why I'm getting the readings I am. Jay __________________ The light at the end of the tunnel is probably the headlight of an oncoming train

9th Jan 2016, 11:34 am	#26
dragonser Heptode Join Date: Aug 2009 Location: Carshalton, Surrey, UK. Posts: 735	Re: Delta-S Soviet Sinclair Spectrum clone Hi, I think the scope probe should work ok with the 169 resistance from probe tip to inner bnc connection. But I wonder if there might be a broken ground connection on the din socket on the computer itself ? [ or even on the scart cable you made up. there may be more than one ground connection required to different pins on the scart ? ] nice to see a picture of the computer on youtube ! regards Peter B