My Sansui 7070 receiver broke a few years back and I have recently
started looking into repairing it. I purchased the schematics for this
system. The two fuses for the rectifier on the F-2625 power supply
board are both blown. I am worried about replacing them and powering
up the system with out knowing why they are blown in the first place.
I do not want to damage the system any further. Any ideas on how to
proceed?

Thank you in advance for your time.

Sincerely,

Marc

Dear Sir,

Thank you for your response. I have been studying the schematics and I
am familiar with the placement of the components on the F-2625 power
supply board and the F-2624 driver board.

My troubleshooting skills are minimal. I was going to check the listed
voltages at various points on the power supply and driver boards i.e.,
output from driver board, voltage across power transisters.

I can check individual components. I am just not sure if you can check
them on the board or if they should be removed and then tested.

I have not noticed any parts that look burnt.

Age and heat probably led to the failure. I stored the equipment in a
stereo cabinet but it did not have proper ventilation.

Any advice or instructions would be greatly appreciated. I have owned
the receiver since 1978 and it has sentimental value.

Sincerely,

Marc

Meat Plow wrote:
On Wed, 10 Jan 2007 15:32:57 -0800, Marc Has Frothed:

My Sansui 7070 receiver broke a few years back and I have recently
started looking into repairing it. I purchased the schematics for this
system. The two fuses for the rectifier on the F-2625 power supply
board are both blown. I am worried about replacing them and powering
up the system with out knowing why they are blown in the first place.
I do not want to damage the system any further. Any ideas on how to
proceed?

Thank you in advance for your time.

Sincerely,

Marc

Check the rectifier for shorts? Know how to do that? Anything else look
burnt? What led up to the fuses blowing? What are your troubleshooting
skills? Would you like detailed instructions on how I would go about
servicing this unit?

--
Pierre Salinger Memorial Hook, Line & Sinker, June 2004

COOSN-266-06-25794

Marc wrote:
Dear Sir,

Thank you for your response. I have been studying the schematics and I
am familiar with the placement of the components on the F-2625 power
supply board and the F-2624 driver board.

My troubleshooting skills are minimal. I was going to check the listed
voltages at various points on the power supply and driver boards i.e.,
output from driver board, voltage across power transisters.

I can check individual components. I am just not sure if you can check
them on the board or if they should be removed and then tested.

I have not noticed any parts that look burnt.

Age and heat probably led to the failure. I stored the equipment in a
stereo cabinet but it did not have proper ventilation.



Probably you are going to need to bring it up on a current limited
bench supply, depening on how many different voltage supplies there are
in the box. The solid state power amps that have a plus and minus rail
are easiest. These things aren't made for easy servicing, making it
tough to unhook unneeded subsystems for test in many cases.

The caps should be tested separately if they can be isolated without
unsoldering from a board. If they come up to rated voltage and hold it,
they should be checked to hold the charge for a long time. Sometimes
bringing them up, letting them sit, and sudden discharge (use wires so
as not to arc the terminals) does them good-or kills them.

There's a case for changing every lytic on the box if it is old enough
to be President.

Fuses usually don't blow without a reason, and the usual cause on solid
state amps is shorted output transistors. The output transistors are the
ones mounted on the big heatsink. If you aren't experienced in electronics
repair, I recommend taking it to someone who is, as someone else said these
can be a very tricky repair. Especially if the outputs blew as a result of
excessive DC bias, a tough problem even for an experienced tech to track
down.

"Marc" wrote in message
oups.com...
My Sansui 7070 receiver broke a few years back and I have recently
started looking into repairing it. I purchased the schematics for this
system. The two fuses for the rectifier on the F-2625 power supply
board are both blown. I am worried about replacing them and powering
up the system with out knowing why they are blown in the first place.
I do not want to damage the system any further. Any ideas on how to
proceed?

Thank you in advance for your time.

Sincerely,

Marc