EMT 244 Cyclic Noise

[plimousse]

Hi All,
A customer of mine came in with the device.
A constant, cyclic noise, speed vary with reverb time.
I have service manual, but without digital section ???
If any have an idea.
Many thanks,
Cheers,
Pascal

 

[radardoug]

Cyclic noise normally is caused by bad ram chips.

 

[plimousse]

Thanks,
I will check that.

 

[plimousse]

Hi all,
The bottom row is loaded with 14 TMS4044 (4096x1), the top row is loaded with 16 AM9102 (1024x1)...
LSB on the left, MSB on the right of the pcb.
Logically, if we follow the service manual, we must have 16 bits (?), why only 14 TMS ?
On each side(2 left, 3 right), ICs have been erased, difficult to trace anything.

Any help would be welcome, because if we remove the memory ICs one by one, the noise stops, then, after a variable delay, starts again

 

[plimousse]

Hi,
Another point,
Without input signal, I have the red led "Register" always ON ?
Not documented section ...
Regards,
P.

 

[radardoug]

Register light being on indicates bad data, so just telling you what you already know. Check the erased chips for continuity to the memory bank, most of the memory bank chip pins will be paralleled, so pretty easy to work out if they are part of the memory bank. If you pull out all the chips, you should have no noise. Then put in MSB, then put in starting from LSB. MSB is sign, so you need that or you cant get +- waveform.