January 29, 1975
SB-634							Bulletin
No:
Station Console						SB-634-1

	                    Mismatch When Using 600 Ohm Input

Change the phone patch control to a 200K/1500/10 Ohm control, [PN 13-16].
Parts available in June 1975.
--------------------------------------------------------------------------------------------------------------------
			February 10, 1975
SB-634							Bulletin
No:
Station Console						SB-634-2

		      Phone Patch Control Miswired

In the first run of SB-634's, the phone patch control is wired with the
front and middle sections interchanged.  This can be corrected by
interchanging the wires going to lugs 2 and 5, and interchanging the
wires going to lugs 3 and 6 of the control.

A mailing is being made to all SB-634 owners that will provide them with
rewiring information.
-------------------------------------------------------------------------------------------------------------------
			June 6, 1975
SB-634							Bulletin
No:
Station Console						SB-634-3

		                 Schematic Error

The connection points K, L, M, N, P and R on the SB-634 schematic are
reversed from their proper order.  For example, point K should be R, etc.
-------------------------------------------------------------------------------------------------------------------
			October 28, 1975
SB-634							Bulletin
No:
Station Console						SB-634-4

		Use of Wider Toleranced Clock Chips

The [PN 443-601] clock chips have been selected for minimum flicker.
The [PN 443-601] is a hand selected version of the [PN 443-687].

With the following changes, hand selection is no longer necessary:

Change C201 from 30 pF to 51 pF [PN 20-190].
Change R237 from 15K to 18K Ohm [PN 1-162].
Change [PN 443-601] to [PN 443-687].

(NOTE:  Either clock chip can be used witht he new value resistor and
capacitor.)
------------------------------------------------------------------------------------------------------------------
			February 2, 1977
SB-634							Bulletin
No:
Station Console						SB-634-5

	                Large Display Tube Part Number Change

+ + + + Information not yet available + + + +
-------------------------------------------------------------------------------------------------------------------
			March 14, 1978
SB-634							Bulletin
No:
Station Console						SB-634-6

		Display Counts Twice Each Second

Check the brand of [PN 443-7] IC's used at IC204.  If it is a TI brand,
replace it with a Fairchild brand.

The TI brand of IC was found to be causing a small glitch on the
positive-going input of IC204 as the signal reached 1 volt, causing one
count from the glitch.  Replacing with a Fairchild brand IC corrected the
problem.

All Replacement Parts stock of [PN 443-7] IC's are now Fairchild brand.
--------------------------------------------------------------------------------------------------------------------	
+ + + + SB-634-7/8/9 are not yet available + + + +  [Sorry]
--------------------------------------------------------------------------------------------------------------------
			November 16, 1984
SB-634						Bulletin No:
Station Console					SB-634-10

		         Dual Electrolytic Capacitor NLA

The 2 x 20 uF electrolytic [PN 25-270] at C211A/B is no longer available
from Heath Parts Replacement.  Two 22 uF electrolytic capacitors [PN
25-955] are used as a replacement.

After the old capacitor is removed from the circuit board, use a sharp
pointed tool and enlarge the negative (-) hole so both negative leads of
the replacement capacitors will fit into the hold.  Bend the leads of the
replacement capacitors so they fit flush with the board.  [[The negative
leads form the bottom of the 'triangle' that is made when the two (+)
leads are placed in their respective holes]].
-------------------------------------------------------------------------------------------------------------------

			August 31, 1989
SB-634							Bulletin
No:
Station Console						SB-634-11

	Minutes or Hours Digits Count Twice As Fast As Seconds

When the minutes or hours display sometimes advances just as if SW2
minutes Set switch [PN 60-6] or SW3 Hours set switch [PN 60-6] were
activated, a high resistance path may have developed across the Set
switch contacts.  Replace the appropriate switch to correct the problem.
--------------------------------------------------------------------------------------------------------------------
That's all I have on the SB-634 [1966-89].  Enjoy!
--------------------------------------------------------------------------------------------------------------------