Topfield SD PVR Power Board Circuit Diagram
Testing the Power PCB
You want to measure the voltages
with the board in place and connected as it would be in normal use. This ensures
that the correct load is placed on each voltage rail and you don't get false
readings. You can measure the voltages, under load with the PVR running, by
touching your multimeter probes to where the wires enter the connector as shown
in the picture on the left. Connect the
negative probe to the black wire on the large connector and use the positive red
probe to test each of the white wires in turn (except the GND ground wires). A zero
voltage could mean that the metal tip of the probe is not contacting the metal
inside the connector.
Do NOT touch any of the aluminium heatsinks as they can contain lethal voltages!
Be VERY careful of the 240v side of the power PCB!
The board needs repairing if any
of the measured 'under load' voltages are different to the specified voltages
(on the circuit diagram or as printed on the PCB) by more than +/- 0.2v, or
0.169v for the 3.3v line. If any of the voltages are zero then you'll
need to replace more components than just aged capacitors (or replace the whole
The voltages for all of the wires are printed onto the
top side of the circuit board as can be seen in the picture on the right. Click on the picture
for a full-size image that is easier to read.
Repairing a Faulty Power PCB
If the voltages on your power
supply are out of tolerance it is likely that a few of the critical electrolytic
capacitors have aged and are out of spec. The capacitors that we are interested
usually Samwha RD Series
1000uF 16V 105°C radial types
- or the same spec/type from another brand. It is common to find different
brands of capacitors on the one board. Ideally
you could upgrade the power supply by replacing them with 1200uF 16V capacitors
RS Components pack of 5 that retails for $7.48
get the low ESR
Jaycar (in Australia), as low ESR
give off less heat under load and are rated for higher temperatures.
Unfortunately Jaycar only has 1000uF 16V low ESR electrolytic capacitors, though
this is still an improvement on the original 1000uF 16V capacitors.
The capacitors you will normally
need to replace are C17, C18, C22 and C23. If you buy a pack of 5 you may as
well also replace C19. If you have a 6th capacitor you may as well also replace
C25, though it's normally not required.
If you look carefully at the photo below you can
see the orientation of the capacitors. The circuit board should also have
markings indicating the polarity of the capacitors. Just make sure you fit the
new ones the correct way around.
Photo by Peter Hagarty
Resurrecting a Dead Power PCB
If the power PCB is completely dead, or has more serious problems than just high
and/or low voltages, you will need to replace more than just a few electrolytic
capacitors. After testing the board and components you will then need to source
suitable replacement components using the circuit diagram above and the markings
on the circuit board and the components themselves to determine the type and
Availability and price will
determine whether it is better to purchase a new replacement PCB or repair the
The life-span of the standard -45° to +105°C rated capacitors depends on their average
temperature. At a constant
105°C the capacitor would only last 2,000
hours (12 weeks if left on 24/7). At 55°C the capacitor would only last 32,000
hours (96 weeks or 1.8 years, if left on 24/7). Not surprisingly many Toppys'
power supplies fail after only 1.5 years.
If you only leave your toppy turned on for 8 hours a day the capacitors could
fail after 5.4 years.
Power Board Connectors
If you intend purchasing a replacement PCB you need to be aware
of the different connector styles that Topfield has used in various vintage SD
Sometime between June 2005 and April 2006 Topfield changed the type of the connectors used where the Power PCB
connects to the Main PCB. The new type of connector has a retaining clip that
requires you to squeeze the clip towards the plug to remove it from the socket
on the Main PCB. The Power PCB has 2 cables that connect to the main PCB (one
small and one large). They are keyed to only fit in one orientation (though you
can force them to fit in the wrong way) and all wires are white except for one
black wire at one end of the connector. This black wire is at the top in the
If you are ordering a replacement Power PCB, or Main PCB, you need to order one
of the correct vintage to make sure that the connectors match your existing
mating part. Of course if you order both a new Power PCB and a new Main PCB then the
type of connector does not matter as you will be buying matching PCBs with the
new connector type.
Mix & Match?
Old type plugs will fit, with a bit force, into new type sockets. But new type
plugs require modifying to fit into old type sockets. Be aware that unmatched
connectors may work loose if you transport the Toppy to a different location.
If required you can unsolder both existing cables on a new Power PCB and solder
in the old type cable from your original Power PCB. In a worst case scenario you
can even cut off the retaining clip and the 2 lugs (on the same side as the
clip) on each end of a new Power PCB's cables' plugs to make the plugs fit into
old type sockets on an old Main PCB.
240v can kill! Be very careful when working inside any 240 Volt appliance. Double check that
you have unplugged the power cord before starting. And do NOT reconnect the
power cord until the top cover has been securely re-attached. Keep children and
pets away while working with electricity or electronics. Beware that for some
time after you remove the 240 volt power source the 240 volt side of the power
board circuit (especially the very large capacitor) can still contain a charge
large enough to injure or kill you. Pressing the Standby button on the toppy,
after unplugging the 240 volt power, should be enough to drain the capacitor.
You should only remove the cover of your Toppy if it is no longer under
warranty. If you are not the owner of the Toppy you must get the owner's
permission before you start. If you are under 18yr you must get an adult to
supervise. While all possible due care and thought has been put into the writing
of this guide, ToppyTools, myself, and any business or person associated with me
or ToppyTools, will not be held responsible if something goes wrong. By
following this guide you are accepting this disclaimer and agree that the only
person responsible for your actions is you.