[TenTec] Corsair II UV EPROM failure

Jerry Haigwood jerry at w5jh.net
Fri Feb 14 20:24:30 EST 2014

     The MC68705 is a microprocessor and not an EPROM.  It does two 
functions.  It counts the frequency and along with some other parts, 
displays it.  And, as you said, it is also a memory keyer.  The MC68705 is 
prone to failure.  A while ago, Steve Hunt, G3TXQ, designed a replacement 
board using two PIC devices.  One is the display and the other one is the 
keyer.  I kitted several of these boards and sold them to Corsair II owners. 
If you ask, you might still find someone on this list who is willing to part 
with their kit.  The kit is a drop in replacement for the TenTec board 
except you do not have any memories in the keyer.  If you want to see what 
one of these looks like, you can peruse Steve Hunt's web page.
Jerry W5JH
"building something without experimenting is just solder practice"

----- Original Message ----- 
From: "A R" <raf_3 at msn.com>
To: "tentec" <TenTec at contesting.com>
Sent: Friday, February 14, 2014 6:43 PM
Subject: [TenTec] Corsair II UV EPROM failure

> My recently acquired Corsair II has a failed logic board UV eprom 
> (MC68705P3S) that prevents me from operating CW. The eprom failure is the 
> keyer "dit" input stuck close enough to a "low", that about 30 minutes 
> after power-up, the eprom temp reaches 50C, and the "dit" input is  low 
> enough that all I have is a continuous, uninterruptable transmitted string 
> of dits. Unfortunately, the architecture doesn't have provision to defeat 
> the keyer function in CW mode. The eprom temp reaches the 50C temp after 
> about 30 minutes, with an ambient temp of 22C.
> I've talked to Garry Green at TenTec, but they don't have any proms for 
> this ancient Corsair II. But, the unprogrammed MC68705P3S's are available 
> elsewhere, and Garry agreed to search the TenTec operation to see if they 
> have the programming fixture and the Corsair II program. I'm hoping that 
> Garry can find the fixture and the program. But, I'm not very optimistic 
> he'll be successful.
> So, my options are to either find a "surplus" programmed CORSAIR II 
> MC68705P3S (anybody have a spare or surplus one?), or modify the Logic 
> Board enclosure to provide forced air cooling in an attempt to keep the 
> processor temp below the critical 50C.......and hope the processor "dit" 
> input doesn't further deteriorate.
> Does anyone have a spare or "surplus" programmed processor for the CORSAIR 
> II?
> Thoughts on cooling/controlling the temp of the processor? Forced air may 
> get the job done (maybe in combination with a dip heatsink bonded onto the 
> processor). But I recall (from a former life) that ss heat exchangers for 
> dips may be a solution that's not as messy as shoe-horning a 25mm pc fan 
> onto the logic board enclosure, but would necessarily contribute a slight 
> ? temp rise in the CORSAIR's interior.
> Any help or suggestions welcome.
> 73,
> Allen---W7GIF
> _______________________________________________
> TenTec mailing list
> TenTec at contesting.com
> http://lists.contesting.com/mailman/listinfo/tentec

More information about the TenTec mailing list