WHTSCSI Missing IC

[Shift838]

My boards only has one GAL the other was replaced with the daughter board.

 

i don’t have the code to reprogram it.

[RickyDean]

Just now, Shift838 said:

My boards only has one GAL the other was replaced with the daughter board.

 

i don’t have the code to reprogram it.

Gotcha, just don't rule it out in the process.

[Shift838]

1 hour ago, RickyDean said:

Gotcha, just don't rule it out in the process.

going to reach out to Richard.

[Shift838]

I'm really thinking the ICs on the card are not getting enough power to perform their functions.  I tested every IC on the board.  All the IC's have a minimum voltage requirement of 4.75v, but a majority of them are getting less than that.  The only ICs getting at least 4.75v are: SRAM, EPROM, 74LS259's,SCSI Controller IC, the rest are getting lower than the minimum voltage required to power the chip correctly.  

 

I have tested all the capacitors and the IC's and annotated them in the attached photo of what they are getting in voltage.  for the voltage regulators the value is the output voltage.  The main capacitors near the voltage regulators are getting right at 5v and the regulators are delivery very close to 5v.  I do see one tantalum that is only at 4.44v. 

 

Suggestions?

 

Edited November 24, 2023 by Shift838

[RickyDean]

41 minutes ago, Shift838 said:

I'm really thinking the ICs on the card are not getting enough power to perform their functions.  I tested every IC on the board.  All the IC's have a minimum voltage requirement of 4.75v, but a majority of them are getting less than that.  The only ICs getting at least 4.75v are: SRAM, EPROM, 74LS259's,SCSI Controller IC, the rest are getting lower than the minimum voltage required to power the chip correctly.  

 

I have tested all the capacitors and the IC's and annotated them in the attached photo of what they are getting in voltage.  for the voltage regulators the value is the output voltage.  The main capacitors near the voltage regulators are getting right at 5v and the regulators are delivery very close to 5v.  I do see one tantalum that is only at 4.44v. 

 

Suggestions?

 

I'd say that the regulators are close to tolerance, it appears that the voltage drops from right to left, mostly, so your losing a half volt, maybe deteriorating components? About the tantalum, is that on the output side? If so, suggest that it should be changed, unless in circuit it's supposed to lose that .6 volts, by design? Could that be drawing the voltage down from the other IC's? I know that on one of the SAMS card I built, I installed a Traco TSR 1-2450 and it would not operate correctly, measured around 4.75 ish (been a couple of years), and when I changed out to a 5volt regulator, it woke up and started working.

[Shift838]

I changed the voltage regulators a few

days ago.

[+OLD CS1]

My first thought is a short somewhere.  Not a complete short, but a failing capacitor would fit the bill.  Did you say you already re-capped?  (If I go back a page I lose my post, and I am too lazy to copy-n-paste.)

[Shift838]

45 minutes ago, OLD CS1 said:

My first thought is a short somewhere.  Not a complete short, but a failing capacitor would fit the bill.  Did you say you already re-capped?  (If I go back a page I lose my post, and I am too lazy to copy-n-paste.)

I have replaced all the ICs that I could replace with the exception of the GALs, replaced the regulators.  I have the caps to recap so that's my next step.

[+FALCOR4]

16 hours ago, Shift838 said:

I'm really thinking the ICs on the card are not getting enough power to perform their functions.  I tested every IC on the board.  All the IC's have a minimum voltage requirement of 4.75v, but a majority of them are getting less than that.  The only ICs getting at least 4.75v are: SRAM, EPROM, 74LS259's,SCSI Controller IC, the rest are getting lower than the minimum voltage required to power the chip correctly.  

 

I have tested all the capacitors and the IC's and annotated them in the attached photo of what they are getting in voltage.  for the voltage regulators the value is the output voltage.  The main capacitors near the voltage regulators are getting right at 5v and the regulators are delivery very close to 5v.  I do see one tantalum that is only at 4.44v. 

 

Suggestions?

 

Maybe start at the regulator where you see +5v and start going down the power path to see if you find a flaw in the +5v trace?  It almost sounds like there might be a point of high resistance somewhere that is causing a voltage drop to all of the subsequent ICs?

[humeur]

You need both 74ls125 otherwise the card does not work.

To check, put for example your card in vintage 1200 with Minimen easy bug type C then C1200 then 1 point to exit and M4000 the return must be AA start of the DSR.

 

 

 

Il faut les deux 74ls 125 sinon la carte ne fonctionne pas.

Pour vérifiez mettre par exemple sa carte en cru 1200

avec Minimen easy bug taper C puis C1200 puis 1

point pour sortir et M4000 le retour doit estre AA debut de la DSR