Netherlands + IC99

[Architect]

Meanwhile the kit arrived in the Netherlands. It really looks great. A job well done, Grant. [Actually, it was there already last Tuesday but it had to fight its way through Customs.]

I studied the LOGIC SCHEMATICS in detail and found that IC99 is not used anywhere. The diagrams I downloaded before (sheet 01) said "CORRECTED 9-20-72". IC99 is also not attached to anything at all on the PCB. I assume it was there in an earlier design but John changed it.

Could that be the reason it runs hot (190 F) as Grant noticed (page 28)? I think it is possible to take out IC99 without changing anything whatsoever. Of course I will try that once I assembled everything, but perhaps you guys can already check that.

[Geoff Harrison]

Originally Posted by Architect

I studied the LOGIC SCHEMATICS in detail and found that IC99 is not used anywhere.

You're absolutely right. You have good eyes.

Could that be the reason it runs hot (190 F) as Grant noticed (page 28)?

My Kenbak has been running continuously for 4 days now with the top on and IC99 is not particularly hot. It is warm, as are all of them, but I can keep my finger on it with no discomfort.

[Grant Stockly]

That heat might have been due to a marginal part.

My incandescent bulb Kenbak has the 190F chip.

My LED Kenbak is just regular warmth.

I don't see any connections (other than power) to the chip either. That's weird.

It doesn't get much more clear than this:

[Architect]

The reason I found out about IC99 is that I made a cross reference table for the ICs because I found myself continuously scanning through 24 diagrams to look for a particular IC. See the attachment.

[Grant Stockly]

Originally Posted by Architect

The reason I found out about IC99 is that I made a cross reference table for the ICs because I found myself continuously scanning through 24 diagrams to look for a particular IC. See the attachment.

Thanks for that list! If there is anything I can do to help you let me know.

I know I promised earlier, but I will have the searchable PDF files uploaded soon.

[Grant Stockly]

Originally Posted by Architect

Could that be the reason it runs hot (190 F) as Grant noticed (page 28)? I think it is possible to take out IC99 without changing anything whatsoever. Of course I will try that once I assembled everything, but perhaps you guys can already check that.

I've been thinking about this more and I can't find a good reason. I can guarantee one thing, it IS hot. Maybe the probe was reading wrong, but I couldn't keep my finger on it.

I thought maybe it was because the inputs were floating and maybe the chip was oscillating. But I am pretty sure the inputs are stable when left unconnected.

When I get a chance I will swap the chip out (on the board that gets hot) and see if it also gets hot.

When do you plan to start construction of your Kenbak?