The screen of my SPX-90 yamaha reverb is showing weird symbols and the unit does not operate anymore. Any idee od the problem? Thank-you

To reinitialize the IS-SPX-1000 unit to its factory default settings:
1.
Unplug the unit from the power.
2.
Push the reset button and keep it pressed.
3.
Power up the IS-SPX-1000 unit.
4.
Wait with the reset button pressed for at least 8 seconds.
5.
Release the reset button.
6.
The IS-SPX-1000 unit will now boot in the factory default mode.

To reinitialize the IS-SPX-1000 unit to its factory default settings:
1.
Unplug the unit from the power.
2.
Push the reset button and keep it pressed.
3.
Power up the IS-SPX-1000 unit.
4.
Wait with the reset button pressed for at least 8 seconds.
5.
Release the reset button.
6.
The IS-SPX-1000 unit will now boot in the factory default mode.v

To many possibilities. The reverb unit or the reverb preamp or the reverb output amp.

Here is a link to the schematic drawing
http://www.prowessamplifiers.com/schematics/fender/ps160.pdf

items to check are
1-the footswitch and plug
2-the reverb unit ,usually found at the bottom of the box
3-the reverb unit is plugged in to the amp
4-V6 a 7025 valve
5- the reverb switch is in the on position

Hope this helps

Len

Best advice would come from Yamaha itself. Here's the link to Customer Service-
Contact Us Support Yamaha United States

One of the 'plate' type reverbs is usually best on vocals. Preset 16, 19 or 26 should be suitable.

Sch: http://www.schematicx.com/schematic/fender-acoustasonic-junior-jr-guitar-amplifier-schematic/

Microphonic tubes can be detected by tapping them lightly with a pencil. I cannot find if this uses a spring reverb, but if it does, vibrating the cabinet will get a clanky type sound from the reverb tank. This MAY use a digital reverb however which is immune to that. Next thing is to make sure your guitar can't "hear" the output sound of the amp because the strings can pick up the sound and resonate feeding back into the amp. You can detect if this is happening by quickly dampening the strings and see if ringing gooes away. You probably need 6 to 10 feet of clearance between the guitar and the amp OR put your body between the amp and the guitar. ALWAYS set sound level at safe levels. Get a sound meter and go no higher than 90 Db. I know a lot of near deaf musicians whose careers are near over because of hearing loss using too high level.