-------------------------------------------------------------------------------------------------------------------
			June 12, 1967
HP-23							Bulletin No:
AC Power Supply						HP-23-1D

                                                   Increase Fuse Capacity

Increase the fuse capacity from 3 Amps [PN 421-2], to 4 Amps SLO-BLO [PN
421-5].  This will avoid needless failure in use and will not overtax the
fused circuits.
--------------------------------------------------------------------------------------------------------------------
			May 23, 1974
HP-23 & HP-23A						Bulletin
No:
AC Power Supply						HP-23-1

	         	    HP-23 & HP-23A Service Guide

Check the resistance to ground at the power plug pins:

	PIN 1		48K OHM
	PIN 3		50K OHM
	PIN 4	                 100K OHM
	PIN 7		ZERO RESISTANCE
	PIN 11		 11K OHM

The filter choke L1 has a resistance of OF 100 ohms.

The silicon diodes used in the HP-23 are standard power diodes rated at
500V PIV & 705MA.

Make forward & reverse resistance measurements on the diodes D1 through
the diode, a resistance reading through the diode, a resistance reading
of about 10 ohm in one direction is correct.  Reversing the leads should
show a reading of 
infinity for a normal diode.  Should the readings be more or less, it
would indicate an open or shorted diode.

Following are the resistance of the transformer windings as measured with
a 11 Megohm VTVM:

	Black to Black	 		  1 OHM
	Red to Red Yellow 			12 OHM
	Brown to Brown Yellow		1.4 OHM
	Brown Yellow to Blue		4.5 OHM
	Green Yellow to Yellow	                     .2 OHM
	Green Yellow to Green	                     .1 OHM
	Green to Yellow		                  .1K OHM

Should you experience fuse blowing, this could be caused by the surge
charging of the filter capacitors.  In the early HP-23 supplies, a 30 AMP
fuse was used.  Now the supply is furnished with a 4 Amp Slo-Blo fuse. 
Note: HP-23A uses circuit breaker.

Check for loose hardware, intermittent solder conections & check ground
connection between the capacitor mounting tab and metal mounting wafer.
--------------------------------------------------------------------------------------------------------------------
			June 21, 197
HP-23A, B						Bulletin No:
AC Power Supply						HP-23-2

	Failure of Power Connector When Used In Service
			
Failure of the HP-23B power connector wiring will occur when the HP-23B
is used on the Service Bench, caused by pulling on the power cable to
disconnect the plug, or as a result of repeated rotation or movement of
the cable while units are being serviced.

These failures can be reduced by changing the 11-pin plug cap to a cap
with cable clamp [PN 440-8].  The clamp prevents lead seperation caused
by the cable rotating in the cap as the unit is being serviced, and will
relieve some of  the strain placed on the connector when the connector is
removed by pulling on the power cable.
-------------------------------------------------------------------------------------------------------------------
			Sept 20, 1976
HP-23B							Bulletin
No:
AC Power Supply						HP-23-3

	          PN 57-27 Replacement Diode Leads Too Short

QA now cuts the leads of diodes to remove them from a strip on which they
are received.  This results in a diode lead length about one inch shorter
than the older diodes.

To use this shorter lead diode at D7 of this power supply, it is
necessary to splice wire onto the leads.

The next producton run of these kits will have the AC switch S1 rewired,
so D7 connects to a switch lug next to the terminal strip; permitting use
of the shorter lead diodes.  The screening of switch S1 position on the
chassis will be changed so that the LV 250 DC and LV 300 DC are
interchanged.

(This change will be in 04 level kits)
--------------------------------------------------------------------------------------------------------------------
			October 13, 1978
HP-23 Series						Bulletin No:
AC Power Supply						HP-23-4

		               Intermittent Operation

Ripple and voltage variations on the DC output lines when the supply is
bumped or vibrated may cause intermittent operation.

Check the twist tab connections on C2 and C4 which may be making poor
connection to the grounded mounting wafer.

Be sure the metal twist tabs are soldered to the wafer.  Also, you may
want to add a wire from lug 4 of terminal strip H [Ground] to the
grounding tabs on capacitors C2 and C4 to insure proper grounding.
------------------------------------------------------------------------------------------------------------------
