30 year old piece of equipment operating pretty much flawlessly for
that entire period. VCC and VEE on the 1448 is +/- 15 volts and the
chip is overheating..... even with inputs and outputs disconnected the
chip still overheats(130 F). I noticed that the manufacturer's sets
the MAX power supply voltages at +/- 15 and understand this was
probably designed on the hairy edge of failure but like I said its
been working for 30 years and replacement chips work no better, what
gives. Power supply can not be adjusted and there are other chips on
the board that require the +- 15. d BTW cooling the chip makes it
work. operating the chip from an external +- 12V power supply makes it
work but modifying the circuit may not be an option. I saw where there
are some CMOS versions of the 1488, I was wondering if they would
handle the +- 15 volts better.


TIA
Jimmie

30 year old piece of equipment operating pretty much flawlessly for
that entire period. VCC and VEE on the 1448 is +/- 15 volts and the
chip is overheating..... even with inputs and outputs disconnected the
chip still overheats(130 F). I noticed that the manufacturer's sets
the MAX power supply voltages at +/- 15 and understand this was
probably designed on the hairy edge of failure but like I said its
been working for 30 years and replacement chips work no better, what
gives. Power supply can not be adjusted and there are other chips on
the board that require the +- 15. d BTW cooling the chip makes it
work. operating the chip from an external +- 12V power supply makes it
work but modifying the circuit may not be an option. I saw where there
are some CMOS versions of the 1488, I was wondering if they would
handle the +- 15 volts better.


TIA
Jimmie


I would hang a small PC fan in there, and call it a modification

On 7-26-2011 20:34, JIMMIE wrote:
30 year old piece of equipment operating pretty much flawlessly for
that entire period. VCC and VEE on the 1448 is +/- 15 volts and the
chip is overheating..... even with inputs and outputs disconnected the
chip still overheats(130 F). I noticed that the manufacturer's sets
the MAX power supply voltages at +/- 15 and understand this was
probably designed on the hairy edge of failure but like I said its
been working for 30 years and replacement chips work no better, what
gives. Power supply can not be adjusted and there are other chips on
the board that require the +- 15. d BTW cooling the chip makes it
work. operating the chip from an external +- 12V power supply makes it
work but modifying the circuit may not be an option. I saw where there
are some CMOS versions of the 1488, I was wondering if they would
handle the +- 15 volts better.


TIA
Jimmie

Can you cut the circuit trace of the voltages (Vcc, Vee) feeding the IC
and strap in a pair of diodes (in series) such as IN914 types in each
supply line? Each diode drops about .7V, so you would end up with about
+/- 13.5V at the IC. If you want even lower voltage at the IC, add in
another diode or two in each supply line. Ensure proper polarity...in
the Vcc supply lines, the diode cathodes would go toward the IC and the
Vee diodes would have the anodes toward the IC. Just a thought. Or, if
you know how much current the device draws through each supply (Vcc and
Vee), you could place a single zener diode in series with the supply
voltages to the IC and the polarities would be opposite of using 1N914
diodes. Just find a zener of about 2.5-3V that is rated at about twice
the current the IC draws from each supply.



N0EDV

On Jul 26, 4:34*pm, JIMMIE wrote:
30 year old piece of equipment operating pretty much flawlessly for
that entire period. VCC and VEE on the 1448 is +/- 15 volts and the
chip is overheating..... even with inputs and outputs disconnected the
chip still overheats(130 F). I noticed that the manufacturer's sets
the MAX *power supply voltages at +/- 15 and understand this was
probably designed on the hairy edge of failure but like I said its
been working for 30 years and replacement chips work no better, what
gives. Power supply can not be adjusted and there are other chips on
the board that require the +- 15. d BTW cooling the chip makes it
work. operating the chip from an external +- 12V power supply makes it
work but modifying the circuit may not be an option. I saw where there
are some CMOS versions of the 1488, I was wondering if they would
handle the +- 15 volts better.

TIA
Jimmie

Hey OT
cmos will handle +- 15volts but runs hot, if it's flawless rail to
rail you won't have a problem they will run hotter if not taken all
the way down town.

73 OM
de n8zu

hey OT

The National DS14c88 is the cmos replacement the specs take it to
+-13volts, at 15volts it draw more current so the loads on the output
have to be low enough to stay below the Pd of I think it was 1300mw
73 OM
de n8zu

While I still remember with the inputs unloaded the outputs won't go
to the rail so both transistors are half way on, thus consuming loads
of power. And creating high Pd.

To test how hot it gets you should take the inputs to - or + and leave
them there.

73
de n8zu

On Jul 27, 7:21*am, Scott wrote:
On 7-26-2011 20:34, JIMMIE wrote:





30 year old piece of equipment operating pretty much flawlessly for
that entire period. VCC and VEE on the 1448 is +/- 15 volts and the
chip is overheating..... even with inputs and outputs disconnected the
chip still overheats(130 F). I noticed that the manufacturer's sets
the MAX *power supply voltages at +/- 15 and understand this was
probably designed on the hairy edge of failure but like I said its
been working for 30 years and replacement chips work no better, what
gives. Power supply can not be adjusted and there are other chips on
the board that require the +- 15. d BTW cooling the chip makes it
work. operating the chip from an external +- 12V power supply makes it
work but modifying the circuit may not be an option. I saw where there
are some CMOS versions of the 1488, I was wondering if they would
handle the +- 15 volts better.

TIA
Jimmie

Can you cut the circuit trace of the voltages (Vcc, Vee) feeding the IC
and strap in a pair of diodes (in series) such as IN914 types in each
supply line? *Each diode drops about .7V, so you would end up with about
+/- 13.5V at the IC. *If you want even lower voltage at the IC, add in
another diode or two in each supply line. *Ensure proper polarity...in
the Vcc supply lines, the diode cathodes would go toward the IC and the
Vee diodes would have the anodes toward the IC. *Just a thought. *Or, if
you know how much current the device draws through each supply (Vcc and
Vee), you could place a single zener diode in series with the supply
voltages to the IC and the polarities would be opposite of using 1N914
diodes. *Just find a zener of about 2.5-3V that is rated at about twice
the current the IC draws from each supply.

N0EDV- Hide quoted text -

- Show quoted text -

Thanks Scott, that was my first thought but I am not allowed to
modify the board... I was hoping the CMOS version of the old chip may
work at the elevated voltage level. Im thinking the one that has
worked all these years was a cherry picked mil spec device, its PN is
751448

Jimmie

On Wed, 27 Jul 2011, JIMMIE wrote:

On Jul 27, 7:21*am, Scott wrote:
On 7-26-2011 20:34, JIMMIE wrote:





30 year old piece of equipment operating pretty much flawlessly for
that entire period. VCC and VEE on the 1448 is +/- 15 volts and the
chip is overheating..... even with inputs and outputs disconnected the
chip still overheats(130 F). I noticed that the manufacturer's sets
the MAX *power supply voltages at +/- 15 and understand this was
probably designed on the hairy edge of failure but like I said its
been working for 30 years and replacement chips work no better, what
gives. Power supply can not be adjusted and there are other chips on
the board that require the +- 15. d BTW cooling the chip makes it
work. operating the chip from an external +- 12V power supply makes it
work but modifying the circuit may not be an option. I saw where there
are some CMOS versions of the 1488, I was wondering if they would
handle the +- 15 volts better.

TIA
Jimmie

Can you cut the circuit trace of the voltages (Vcc, Vee) feeding the IC
and strap in a pair of diodes (in series) such as IN914 types in each
supply line? *Each diode drops about .7V, so you would end up with about
+/- 13.5V at the IC. *If you want even lower voltage at the IC, add in
another diode or two in each supply line. *Ensure proper polarity...in
the Vcc supply lines, the diode cathodes would go toward the IC and the
Vee diodes would have the anodes toward the IC. *Just a thought. *Or, if
you know how much current the device draws through each supply (Vcc and
Vee), you could place a single zener diode in series with the supply
voltages to the IC and the polarities would be opposite of using 1N914
diodes. *Just find a zener of about 2.5-3V that is rated at about twice
the current the IC draws from each supply.

N0EDV- Hide quoted text -

- Show quoted text -

Thanks Scott, that was my first thought but I am not allowed to
modify the board... I was hoping the CMOS version of the old chip may
work at the elevated voltage level. Im thinking the one that has
worked all these years was a cherry picked mil spec device, its PN is
751448

So?

It's a line driver, not ttl. It would start with "75" from some
manufacturers.

If it's worked all this time, then look at it from a different angle. The
IC has gone bad in such a fashion that it works at lower voltages.
Replace the IC, and likely it will go back to working. The heat issue may
be that it's bad, not because it's receiving too much voltage.

After thirty years, don't suddenly think the issue is too much voltage.

If the IC was working and doens't now, then I wouldn't trust it even at
lower voltages. But if you're fussing over supply voltage, then reveal
what else uses the +-15v lines, chances are good they aren't fussy either
(whereas the voltages to the line driver define the RS-232 levels and
someone may have deliberately chosen to go for the maximum RS-232 voltages
rather than lower voltages that may not be so obviously high and low.

Michael VE2BVW

On Jul 27, 8:35*pm, Michael Black wrote:
On Wed, 27 Jul 2011, JIMMIE wrote:
On Jul 27, 7:21*am, Scott wrote:
On 7-26-2011 20:34, JIMMIE wrote:

30 year old piece of equipment operating pretty much flawlessly for
that entire period. VCC and VEE on the 1448 is +/- 15 volts and the
chip is overheating..... even with inputs and outputs disconnected the
chip still overheats(130 F). I noticed that the manufacturer's sets
the MAX *power supply voltages at +/- 15 and understand this was
probably designed on the hairy edge of failure but like I said its
been working for 30 years and replacement chips work no better, what
gives. Power supply can not be adjusted and there are other chips on
the board that require the +- 15. d BTW cooling the chip makes it
work. operating the chip from an external +- 12V power supply makes it
work but modifying the circuit may not be an option. I saw where there
are some CMOS versions of the 1488, I was wondering if they would
handle the +- 15 volts better.

TIA
Jimmie

Can you cut the circuit trace of the voltages (Vcc, Vee) feeding the IC
and strap in a pair of diodes (in series) such as IN914 types in each
supply line? *Each diode drops about .7V, so you would end up with about
+/- 13.5V at the IC. *If you want even lower voltage at the IC, add in
another diode or two in each supply line. *Ensure proper polarity...in
the Vcc supply lines, the diode cathodes would go toward the IC and the
Vee diodes would have the anodes toward the IC. *Just a thought. *Or, if
you know how much current the device draws through each supply (Vcc and
Vee), you could place a single zener diode in series with the supply
voltages to the IC and the polarities would be opposite of using 1N914
diodes. *Just find a zener of about 2.5-3V that is rated at about twice
the current the IC draws from each supply.

N0EDV- Hide quoted text -

- Show quoted text -

Thanks Scott, that was my first thought but I am not allowed *to
modify the board... I was hoping the CMOS version of the old chip may
work at the elevated voltage level. Im thinking the one that has
worked all these years was a cherry picked mil spec device, its PN is
751448

So?

It's a line driver, not ttl. *It would start with "75" from some
manufacturers.

If it's worked all this time, then look at it from a different angle. *The
IC has gone bad in such a fashion that it works at lower voltages.
Replace the IC, and likely it will go back to working. *The heat issue may
be that it's bad, not because it's receiving too much voltage.

After thirty years, don't suddenly think the issue is too much voltage.

If the IC was working and doens't now, then I wouldn't trust it even at
lower voltages. *But if you're fussing over supply voltage, then reveal
what else uses the +-15v lines, chances are good they aren't fussy either
(whereas the voltages to the line driver define the RS-232 levels and
someone may have deliberately chosen to go for the maximum RS-232 voltages
rather than lower voltages that may not be so obviously high and low.

* *Michael VE2BVW- Hide quoted text -

- Show quoted text -

But the new chips behave the same as the old, I got it working by
mounting a cooling fan over it.


Jimmie

I suspect you unintentionally shorted one output. While these are
short-protected, they do run hot when this happens.

Check the output volgate on the outputs: pin 3, 6, 8, 11 (this is from heart,
pls verify). If it is either +15 or -15 you're OK, if it is
significantly different you found your root cause.
Pls also check voltages with the chip removed (socketed?).

Typical cause for this is an incorrect serial cable and/or broken serial
connecter (bent pins?), or bad internal connector (flatcable incorrect).
The art to make correct serial cross cables has been largely lost in
30 years and I suspect that's your cause.

73,

Geert Jan PE1HZG