Msg: 6755 *Conference*

08-12-96 14:14:52

From: RON WIESEN

To : MIKE LANE

Subj: REPLY TO MSG #6751 (REPLY)

Well Mike I'm a bit surprised at the results.  Your last message, quote "I did
hear the click for OUT160,1 but nothing whatsoever for OUT160,0 OUT178,12 and
OUT178,12", is probably a typo error regarding the (duplicate) OUT178,12
commands.  I'll assume you meant "I did hear the click for OUT160,1 but nothing
whatsoever for OUT160,0 OUT178,12 and OUT178,4".
 
Your additional info about a "dedicated" phone jack helps.  With a dedicated
jack then I assume you do not attach a telephone instrument (to the GREY cable)
when you use the M100 modem.  Therefore, the first relay can't be at fault
(fails to disconnect the telephone instrument).  But I'm puzzled.  You say you
hear the "CLICK" for OUT160,1 so this relay pulls in (to disconnect telephone
instrument).  But you don't hear "CLACK" for OUT160,0 so the relay doesn't
release.  Perhaps you did OUT160,0 by itself without OUT160,1 beforehand, in
which case the relay was already released so no "CLACK" would be heard.  This
doesn't account for the line seizure however, so I'll ignore this curiousity.
 
As to the second relay, it looks like we've found the problem.  Or at least
we're real close to it.  If OUT178,12 gives no "Tink" sound, then the second
relay either won't pull in or it's already pulled in.  If it won't pull in,
that doesn't account for the line seizure.  If it's already pulled in, THAT
WILL SEIZE THE TELEPHONE LINE ANY TIME THE DIRECT CONNECT MODEM CABLE IS
ATTACHED TO THE LAPTOP!  Perhaps the relay is permenantly pulled in due to
"welded" contacts (took a heavy line surge in a storm) or a mechanical
obstruction.  I recommend that you use your good laptop and do the OUT178,12
test so you get accustomed to what the "Tink" sounds like.  Then do the
OUT178,12 test on the failing laptop.  If you hear "tink" on the good laptop
but not on the other laptop, it most likely that the second relay is
permenantly pulled in.
 
Here's a schematic that shows the circuitry relevent to permenant line seizure
problems.  You or someone with basic electronics experience can diagnose the
component failure.  Note that D18 may be damaged (a surge event triggered D18
but still welded relay contacts) such that it's DC resistance is low enough to
seize the telephone line.  So if you find that the relay has "welded" contacts,
check D18 after you remove the relay but before you install a replacement
relay.
 
.                                                    A25
.                                              +--------------+
.                                 RTS(not)     |              |
. +----------------------------------------------Port B bit 7 |
. |                               RS232C(not)  |              |
. |     +----------------------------------------Port B bit 3 |
. |     |                                      |              |
. |  +-----+M34                                +--------------+
. |   \NOT/
. |    \ /                    Gnd-+
. |     v  M26                    |e
. |     | +----                +--|-+
. |     +-|    \               | |/ |
. |       |NOR  >----+---R49-----k  | T7
. +-------|    /     |        b| |\ |
.         +----     R48        +--|-+
.                    |            |c
.               Gnd--+    RY2     |
. Phone                 +------+  |
. Connector             |      |  |        OT1
----------+     +6VDC-----uuuu----+     +--------+
.         |             |      |        |        |
.   pin 7 o---------+-----o  o-----+------b II d---
.         |         |   | ==== |   |    | b II d |
.         |        D18  +------+  D24   | b II d---
.         |         |              |    | b II d |
.   pin 3 o---------+--------------+------b II d---
.         |                             |        |
----------+                             +--------+
.
.
.  +-----------+--------------------+-------------------------+
.  | Component | Description        | Radio Shack part number |
.  +-----------+--------------------+-------------------------+
.  | D18       | Surge Absorber     | ADX-1864                |
.  | D24       | Surge Absorber     | ADX-1863                |
.  | RY2       | Relay              | AR-8159                 |
.  | T7        | Transistor         | AA-2SC2603              |
.  | M26       | Integrated Circuit | AMX-5811                |
.  | M34       | Integrated Circuit | AMX-5809                |
.  | A25       | Integrated Circuit | AMX-5807                |
.  +-----------+--------------------+-------------------------+
 
In normal operation, the TERMinal mode of TELCOM asserts RTS (Request To Send)
and deasserts RS232C by setting Port B, respectively, bit 7 as ZERO and bit 3
as ONE.  This satisfies NOR-gate M26 which biases transistor T7 to conduction.
Current through the solenoid of relay RY2 pulls in it's contacts.  The contacts
connect the low DC resistance of the outboard winding of transformer OT1
directly across the telephone line which is attached at pins 7 and 3 of the
Phone Connector.  The low resistance is a line seizure where it persists long
enough.
 
For pulse dialing, TELCOM interrupts and then restores the current through the
solenoid of relay RY2 to form digit-pulse trains at a rate consistent with
dial-pulse requirements.
 
Let me know how you make out Mike.  If you need more help, send more messages
but note that I may not check in daily this week because I'm on the road
through Friday.  I'm sure I'll get a chance to check in at least one more time
this week however.