GUBBINS@RADC-TOPS20.ARPA (Gern) (02/01/88)
Zenith H/Z-100 Upgrade Series Part 3 26-JAN-88
Gern
It is well known that the overall quality of electronic equipment is in
direct proportion to the capability of the power supply.
The Zenith Z-100 Power Supply
-----------------------------
The Z-100 power supply provides regulated voltages for the Z-100 main
system components and the S-100 expansion bus. The power supply comes in
two basic external designs, one for the All-In-One (Z-120) and one for the
Low Profile (Z-110). The two power supplies look different on the outside,
but internally they are identical.
The power supply of the Z-100 is a Switching Power Supply. In this type of
power supply, the rectified line voltage is switched on and off at a very
high frequency. The resulting squarewave is then filtered into a DC
voltage. This type of a design results in a power supply that is very
efficient and much lighter in weight than linear supplies.
The Z-100 Power Supply is rated at 240 Watts. It will operate from 120VAC
or 240VAC (switchable) line input at 50Hz or 60Hz. It has its own internal
high capacity cooling fan (which makes it rather noisy in quite
environments). By comparison, the power supply rating of the IBM-PC is 65
Watts, IBM-XT is 135 Watts, Zenith Z-150 is 165 Watts, IBM-AT and Zenith
Z-248 is 200 Watts.
ZDS states that the power supply is not considered to be field serviceable.
If it ever becomes defective, it should be exchanged or returned to an
authorized service center. The current going rate to replace the Z-100
power supply through ZDS/Heath/Factory Service is about $280.00.
[ ZDS does not provide any internal information or schematics on the Z-100
power supply. However, I have obtained complete schematics and the circuit
description. I will provide the schematic as part of the promised
H/Z-100-info-packet USnailing and I will place a file containing the
Circuit Description into the PD Library. The complete theory of the Z-100
power supply operation can be found in this file. ]
Z-100 Power Supply Outputs:
---------------------------
VDC Variance Amps Max Max Ripple
--------------------------------------------------
+5VDC +3%,-3% 12 100mV pp
+12VDC +5%,-5% 5.2 120mV pp (Requires +5V@6 Amp Load)
+8VDC +10%,-5% 8 120mV pp
+16VDC +20%,-10% 1 150mV pp
-16VDC +20%,-10% 1 120mV pp
+12VDC +5%,-5% 1.5 50mV pp (Z-120 Supply Only)
Unofficial Notes on the Z-100 Power Supply:
-------------------------------------------
Both the Z-110 and Z-120 power supplies are internally the same, however
there are different versions of each. The Z-120 (All-In-One) contains an
extra +12VDC connector to power the video monitor. The case of the Z-110
supply is a rectangle, whereas the case of the Z-120 is like a small
triangle on top of a flat rectangle. The Z-120 supply case is made not to
conflict with the space used by the video monitor (a Z-110 would conflict).
The Z-110 supply case is designed not to conflict with the space used by
the disk drives (the Z-120 would conflict).
I am not very familiar with the history of the Z-120 supply, however, there
are three different versions of the Z-110 supply. The original Z-110
supply case was Black with no extra power connector for the winchester
controller board. This +5VDC connector can be easily added to the Black
unit for use with the ZDS winchester controller card (use the same gage
wire!). The second version had a brass colored case and included the
winchester card connector. The current Z-110 supply is silver in color. I
am not aware of any functional differences from the brass version. The
only Z-120 supplies I have seen have been brass in color. A Z-120 or Z-110
supply can be converted to the other simply by changing cases and
transfering the +12VDC video connector.
Self Field Repair
-----------------
The Z-100 Power Supply IS repairable. I am not an expert in Z-100 power
supply repair and it is sometimes best left to capable service technicians.
However, supplies that die/fry after many hours of faithful operation seem
to fail in similar ways and are usually repairable by anyone slightly
skilled in the use of a soldering iron. These are my collective repair
notes:
The Z-100 power supply is quite safe if unplugged and disassembled. This
is providing R1-R4 properly discharge C5 and C6 (the two big capacitors).
Play it safe and make sure C5 and C6 are discharged with a meter and/or
discharge them through a resistor. I DO NOT RECOMMEND WORKING WITH THE
SUPPLY POWERED ON UNLESS YOU REALLY KNOW WHAT YOU ARE DOING WITH THE PROPER
TOOLS AND ARE VERY CAREFUL. There are several hundred volts and several
Amps at various points - it can easily KILL. DO NOT WORK WITH IT POWERED
ON IF YOU ARE ALONE!
The Z-100 supply will not turn on without a proper load.
The Z-100 power supply (as well as other ZDS computer supplies) appear to
have many failures due to poor/cold solder joints. Even worse, these bad
solder connections in the high power circuits have caused arcing and
burn-throughs. Also, some supplies have shown burn-throughs in the high
power circuits induced by surges and other nasties. Inspect the components
for damage (heat scoring, broken leads, etc). Inspect the PC Board for
cold solder joints (dull looking solder connections), heat scoring
(common!), and traces damaged by heat and arcing. I have seen a couple of
supplies that in the same corner had heat/arcing damage that ate the PC
board trace and/or component connection completely away. Repairing the
damaged trace(s) and connections fixed the supplies. Heating more solder
to cold solder joints have repaired other supplies as well.
If the supply was blown by an external cause such as shorting an output,
usually only the output regulator 'double-diodes' need to be replaced.
If the fuse blows after replacing, then Q1 and/or Q2 are fried and must be
replaced. This usually means the supply is in serious trouble and IC1
and/or IC2 and/or a pair of output diodes are fried as well. I can only
wish you the best of luck. Borrow a known good supply and using a
multimeter compare the internal resistances of all leads of the
semiconductors (diode forward bias test preferred). Q1, Q2, and the output
'double-diodes' can only be properly diode tested when removed from the
circuit, but comparison in the circuit with values from a good supply can
zero in on a problem.
The Z-100 Power Supply Fan Noise
--------------------------------
The Z-100 Power Supply has its own internal high capacity cooling fan. It
is rather noisy especially in quite environments. It is the biggest point
of discontent of Z-100 users. After some research and experimentation, I
had hoped that I could make a satisfactory recommendation to reduce or
eliminate the noise level. These are my findings:
The Z-100 power supply fan is a Panaflo FBP-08B12H made by Panasonic. The
relevant specs on it are 12VDC normal, 4.5 mmH2O Air Pressure, 0.8 m^3/min
Min Air Flow (32.9 CFM - Cubic Feet per Minute), 39dBA typical - 45dBA Max
Acoustical Noise. This is for the Z-100's 240 Watt supply.
By comparison, the Z-150 power supply fan is a Panaflo FBP-08B12L made by
Panasonic. The relevant specs on it are 12VDC normal, 2.6 mmH2O Air
Pressure, 0.55 m^3/min Min Air Flow (27 CFM), 32dBA typical - 37dBA Max
Acoustical Noise. This is for the Z-150's 165 Watt supply.
The Z-100 supply is 240 Watts of output power. That is a lot of power that
can be generated for the size of the supply and a proportional amount of
heat that must be removed. Excessive heat destroys components (especially
sensitive are semiconductors). Zenith would have used a quieter fan if
they could. Therefore I must recommend maintaining the 32 CFM air flow
rating of the fan. To provide any less airflow MAY greatly shorten the
operating life of the power supply.
What Can Be Done To Reduce The Fan Noise
----------------------------------------
Bend the vent blades on the back of the computer so that the blades are
straight out and do not impede the flow of air.
Cut out the vent areas in the power supply case and replace with screen
wire or other wire fan guards. This actually increases the air flow.
Attach a large flexible hose (clothes dryer type, etc...) to the back of
the Z-100 and route the noise elsewhere (under a desk, etc...). [ I think
this is a little silly. ]
You could build/buy a large and heavy linear supply that is capable of the
same outputs. These were common in most S-100 computer 'mainframes'. It
would probably require no fan at all. [ I'd wait until I couldn't get any
broken Z-100 power supplies repaired.]
The fan can be replaced with a 32 CFM, 3.14 inch square, AC fan. I tried
the Radio Shack #273-242 at 32 CFM, 38dBA. Unplug (hard if glued) and
remove the DC fan and replace with the AC fan. The AC fans are usually a
bit thicker and may not fit if used with the plastic ring in the supply.
Be Creative! The Radio Shack fan was somewhat quieter, it had a completely
different 'whoosh' to it that was lower in pitch and most people should
find more preferable. Solder the AC fan leads directly to the power
switch. The fan will run even if the supply has shut down due to a fault.
Note that Radio Shack #273-243 is a 3.14 inch, DC fan, 34dBA, but only 27
CFM. I would not recommend this, but it is much quieter, physically fits
in the space of the Z-100 fan, and plugs into where the Z-100 fan did.
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Next: The Z-100 Boot Monitor Upgrade.
INFO-HZ100 is a ]]] FORUM [[[ of discussion of Zenith Z-100 topics. If you
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Cheers,
Gern
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