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Northstar floating point card
- Thread starter Gary C
- Start date
Gary C
Veteran Member
Ah ha !
Just realised that I had put EN-I to pin 13 of CONP PROM as the N* schematic has the pins the opposite way around to the Kicad symbol. It wouldn't matter from an operational point of view as they are both chip enable lines, however it makes a big different on the PCB and is stopping me from routing the tracks as original.
Was driving me mad trying to work out how they got it to jump over another track !
One more step closer
Also, are there any equivalent to the 74S287 PROMS that use much less current ? the power budget just for the PROMs is about 1A !
Just realised that I had put EN-I to pin 13 of CONP PROM as the N* schematic has the pins the opposite way around to the Kicad symbol. It wouldn't matter from an operational point of view as they are both chip enable lines, however it makes a big different on the PCB and is stopping me from routing the tracks as original.
Was driving me mad trying to work out how they got it to jump over another track !
One more step closer
Also, are there any equivalent to the 74S287 PROMS that use much less current ? the power budget just for the PROMs is about 1A !
Gary C
Veteran Member
Layout completed but needs final QA check (already found one missing track because I didn't put Gnd and Vcc to an IC on the schematic)
Realised though, that it uses about £100 of PROMs ! Will have to look carefully for some value job lots.
Realised though, that it uses about £100 of PROMs ! Will have to look carefully for some value job lots.
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daver2
10k Member
The Signetics 82S27 should be pin compatible with the 74S287. However, these may still be unobtanium...
I did order some AM27S13 PROMs as spares for a certain computer system we run. These are 512x4 (so twice as large as the 74S287) with one of the active low chip select lines (pin 14 /G2) of the 74S287 available as an additional address line. Depending on the use if this pin (I can't read the schematic in sufficient detail) you may be able to use the larger part we have in stock. This may help you, but no one else though...
Dave
I did order some AM27S13 PROMs as spares for a certain computer system we run. These are 512x4 (so twice as large as the 74S287) with one of the active low chip select lines (pin 14 /G2) of the 74S287 available as an additional address line. Depending on the use if this pin (I can't read the schematic in sufficient detail) you may be able to use the larger part we have in stock. This may help you, but no one else though...
Dave
daver2
10k Member
The N* FPB PROM looks to be compatible with the 6301 PROM used on the Apple 1 - and there are modern pinout-compatible FPGA replacements for these on Applefritter.
Just another thought...
Dave
Just another thought...
Dave
Gary C
Veteran Member
A 74S571 looks the best bet. Tristate and same pinout (except the A8 line instead of the gate but my Apple-1 uses the same, just need to ensure the data is in the right, or both halves)
Can get these for a reasonable price
but all in, its not cheap in IC's
Can get these for a reasonable price
but all in, its not cheap in IC's
Gary C
Veteran Member
Anyone know a part number / source of the dual TO-220 heatsink of this style ?
EDIT Ah, Wakefield 680-5220
EDIT Ah, Wakefield 680-5220
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In the interest of making this board "period correct" using a single 5V 3A switching regulator in a TO-3 footprint (ie the EZSBC PSU5) wouid be out of the question?
Gary C
Veteran Member
Gary C
Veteran Member
parts on their way. Found some SN74S571N for peanuts (75p each), just hope they are blank ! (and genuine) and most of the other IC's are ordered from Cricklewood and ones that were >£2 I have found on Ebay
Just need the final, final, final QA check then off to JCL
Bet it doesn't work...
Just need the final, final, final QA check then off to JCL
Bet it doesn't work...
jlang
Experienced Member
The chance of zero errors is pretty slim. It's still worth the effort.
Troubleshooting is going to be .... interesting ;^)
daver2
10k Member
If it was easy, everyone would be doing it...
Dave
Dave
Gary C
Veteran Member
Yes, with the dazzler we found a couple of tracks I had missed to ground, but at least they were an easy fix.
Gary C
Veteran Member
maxtherabbit
Veteran Member
SMPS... YUCK
daver2
10k Member
Ditto - I would stick with the TO220 linear regulators.
A bit more heat, true to the original - but they are 'safe' and still very available.
Dave
A bit more heat, true to the original - but they are 'safe' and still very available.
Dave
Chuck(G)
25k Member
Switch-mode regulators run cooler, are more efficient and generally have better regulation. There are several vendors of drop-in replacements for the 78xx TO-220 jobs. The only downside is a bit of low-level noise at the switching frequency (mostly matters in audio circuits). You can also get rid of that big heatsink.
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maxtherabbit
Veteran Member
if I cared about heat production and efficiency I would not be interested in vintage computing
Chuck(G)
25k Member
That's an odd sentiment--"I like them because they produce component-aging heat". But hey, it's your show--use a dynamotor if that floats your boat.
norwestrzh
Experienced Member
Be careful of EZSBC. I ordered one of those high current TO-3 footprint regulators (quite expensive, BTW) from them a while back to replace the regulator on an ADC Super Six. It failed on first power up. I tried to get help or advice from EZSBC about the problem, but all my communication attempts went unanswered. Not even an offer to replace the failed part. I'll never buy anything from them again. Use Polu (sp?).
Roger