Heathkit IP-18 Power Supply Use and Repair

Not being one to read the manual (RTFM) I bought a used IP-18 and tried to use it to charge a gel cel - don't do this!  Q4 will catch on fire!  Q5 will be crispy too! Flames and smoke come out of the case!  Q4/Q5 are 2N3393 which don't seem to be available any longer.  I substituted them with some MPSA06RLRAG somewhat generic NPN amplifier transistors.  The pin-out is different so observe any  change.

As I have two of these units I compared the working and non working voltages and resistances until they were about the same.  Here is the final chart of the 'stock' and the repaired units with Q4/Q5 replaced.

They both seem to be working at this point.

Heath HP-18

Some Voltage and Resistance Readings

Stock Repaired unit

Q3
E .7-16.1 .6-18.1
B 1.1-16.5 1.0-18.6
C 29.2 29.2



D5 + .6 .6
D5 -    .7              .6

#3(open) 20.1 21.1   Terminal Strip shorting bar removed

Q4
E O 0
c 18 1.5-18
b .6 .6


Q5
E .7-16 .6-18.1
C .6-17.1 1.5-19
B .7-16 16.6-16 .6-18 (4.1-18 CURRENT POT)

Q2
E 1.2-16.5 1.0-18.6
C 29.2 26.6
B 1.7-17 1.4-19.4

D3
- 23.9 22.7 OK
+ 19.6 18.0

D4
- .8 3.4
+ 19.3 17.6
ACCROSS 20.1 21.1    OK

Q1
G 1.7-17 1.5-19.2
D 28.6 26.2
S 1.7-17 3.5-21

AC REF
GR-GR 34AC 32AC OK


RESISTANCE
METER ON 200K
Q3
RED TO +
BLK TO

E 0 0
B 4 (VARIES) 4.2 (Varies)
C 22.4 23.4

RED TO -
BLK TO
E 3.5 2.2
B         (VARIES)      (VARIES)
C 23.4 23K (VAR)


Q4
RED TO +
E 3.4 3.4
B 7.4 5.7-11
C 23.4 VARIES UP