I just got to say this is quite an undertaking and I am happy somebody took the time to put this wonderful computer down in a replica PCB. I was helping another member on the Spectrum For Everyone FB Group, who ran into this issue, It appears the footprint for D17 and D15 are actually DO-35 instead of DO-41.
as you can see the inside measurement of the through hole is .55 mm.
The MIC datasheet for the BA157 specifies the standard diameter of the pin (and footprint) as DO-41 which is .77 mm +/- .7mm (included below for your review)
I see you state in your live BOM that the BA157 from MIC fits -- I am wondering if that diode that you installed on yours is a mislabeled (or relabeled) .5 amp fast recovery diode of some manufacture? The interesting thing about that is - that most fast recovery DO-35 Diodes recover (significantly) faster than 1A diodes. The minimum recovery time for the BA157 - 159 seems to be 500nS, as were most 1/2 Amp rectifiers recover much much faster. A 1Kv .5A rectifier will also most likely perform just fine as a rectifier at 110Khz (if I recall correctly the speed of the oscillator in this particular inverter). Additionally, if the board is built using a modern SRAM replacement for the lower 16K, or 5v Equivalents such as 4164 or 41256 the likelihood of the video amp even exceeding 200mA is low. I did calculations on the 4116's a few weeks ago when I was rebuilding the DC-DC converter on my issue 4 -- the most the ram chips can draw functioning normally is 240mA. The video amp is less than 100mA ... meaning the diodes in the circuit are oversized by ~50%. That's not a bad thing and I would say its common practice in a power circuit to err on the side of caution always.
But in this case I think its most likely going to be well below 500mA if only using 5v rail for the ram chips, and 12v for the Video amplifier.
At any rate. I provide the footprint specifications below if you would like to update the footprint on your PCB. And it might be prudent to update your live BOM.
Thanks for doing all the leg work on this wonderful PCB! I think its great we can get a top masked PCB with the latest revison 48k Spectrum in 2024.
Hello,
I just got to say this is quite an undertaking and I am happy somebody took the time to put this wonderful computer down in a replica PCB. I was helping another member on the Spectrum For Everyone FB Group, who ran into this issue, It appears the footprint for D17 and D15 are actually DO-35 instead of DO-41.
as you can see the inside measurement of the through hole is .55 mm.
The MIC datasheet for the BA157 specifies the standard diameter of the pin (and footprint) as DO-41 which is .77 mm +/- .7mm (included below for your review)
I see you state in your live BOM that the BA157 from MIC fits -- I am wondering if that diode that you installed on yours is a mislabeled (or relabeled) .5 amp fast recovery diode of some manufacture? The interesting thing about that is - that most fast recovery DO-35 Diodes recover (significantly) faster than 1A diodes. The minimum recovery time for the BA157 - 159 seems to be 500nS, as were most 1/2 Amp rectifiers recover much much faster. A 1Kv .5A rectifier will also most likely perform just fine as a rectifier at 110Khz (if I recall correctly the speed of the oscillator in this particular inverter). Additionally, if the board is built using a modern SRAM replacement for the lower 16K, or 5v Equivalents such as 4164 or 41256 the likelihood of the video amp even exceeding 200mA is low. I did calculations on the 4116's a few weeks ago when I was rebuilding the DC-DC converter on my issue 4 -- the most the ram chips can draw functioning normally is 240mA. The video amp is less than 100mA ... meaning the diodes in the circuit are oversized by ~50%. That's not a bad thing and I would say its common practice in a power circuit to err on the side of caution always.
But in this case I think its most likely going to be well below 500mA if only using 5v rail for the ram chips, and 12v for the Video amplifier.
At any rate. I provide the footprint specifications below if you would like to update the footprint on your PCB. And it might be prudent to update your live BOM.
Thanks for doing all the leg work on this wonderful PCB! I think its great we can get a top masked PCB with the latest revison 48k Spectrum in 2024.
you can view the datasheet here: http://www.cnmic.com/DesktopModules/HT/BLOB/BA157%20THRU%20BA159.pdf
You can view the DO-35 specification here: https://www.mouser.com/PCN/Microsemi_Corporation_DO_7_to_DO_35_customer_letter.pdf
and lastly the DO-41 specification here: https://www.diodes.com/assets/Package-Files/DO-41-Plastic.pdf