My A500 doesn´t display image on some demos, why ?

[scannercf]

 recently have bought an Amiga 500, and I found a little problem that i can´t fix out.
 
The computer doesn´t show image when I try to run some demos, while the audio runs perfect (if the machine don´t hang up).
 
This is my Amiga ...
 
Motherboard rev. 5
Agnus 8372a
Eureka 512 in trap door
Supra Drive 500XP with 2 Mb.
1010 disk drive.
1084 monitor connected through RGB cable.
PSU 110v.
 
Sysinfo tells this :
 
DMA/Gfx : ECS Agnus 1 meg.
Mode: PAL
Display: Std. Denise
CPU/Mhz: 68000
FPU: NONE
MMU: N/A
VBR: N/A
Horiz Khz: 15.72
Eclock: Hz: 715909
Ramsey Rev: N/A
Gary Rev: N/A
Card Slot: NO
Vert Hz: 60
Supply Hz: 60
 
I found some there that doesn´t fit the standards ... the processor runs a NTSC speed , the frecuency is the NTSC frec., but the machine is in PAL mode, maybe this is the problem, but I don´t know how to fix it.
 
I you can ... please hel me !!!
 
Thank you very much.
 
 
Claudio

[scannercf]

I found the solution !!

I found two little programs incluided into the Kill2090.lha archive in Aminet.
These programs are called "ResetPAL" and "ResetNTSC", what they do is force the 8372a to PAL or NTSC mode, and when I run the "ResetPAL" the machine changes to 50 Hz,  7.09 Mhz 68000 ... and the demos works ok.

Thanks to everybody who tried to help me !!!

Claudio