I "repaired" the counterweight. i removed what's left of the leaf spring. The counterweight have 2 counterweights insisde. a little one suspended only by rubber, and a big one suspended with the leaf spring and a rubber. The rubber that suspended the little counterweight was in good shape, but too soft to hold the 2 counterweight, so i removed it(and put it in a safe place) and replaced with silicone. then i secured the big counterweight to the cage with the screw in the rear. The glued the counterweight to put all in place, but made sure i can dissassemble it again if i got a new leaf spring.
The result is similar to the counterweight on other dual turntables.
I put a AT440mla and tried the turntable. I got sound in both channels, and good tracking. The only problem is the sound is too bright and a little hum and hiss, but i think the culprit is my cheap preamp. I searched reviews of my preamp, and other people got the same results with it.
auto stop sometimes works ok, but other times the tonearm reaches the rest position and lowers, then the turntable shuts off, and then it powers on again, raises the tonearm, and repeat the stop cycle, and then shuts of again. this is an infinite loop until i unplug the turntable and make the platter spin backwards and that sometimes reset the mechanism.
same behaviour with auto start. instead of enter the start cycle it enters the stop cycle in an infinite loop. sometimes when i just reseted the mechanism it works fine once.