echoplex ep-4, major rebuild, help, questions

[spgjmf]

hi folks, first post on this forum. I have an ep-4 plex which has seen better days.
I bought a new tape cart from orbit electronixs and fired it up. motor runs. direct signal is load and clear, but no echo. all I get from the echo side is a white noise rumble noise.
not hissy. I checked the heads - erase is 29ohms, but the rec and play back don't read at all ( open) - so it seems like they are bad - right? how can I confirm, double check them??

are replacement head available? what else could I test/measure and confirm the heads are bad. of interest, the unit is an ep-4, but it has no compressor board and the circuit as compared to the schematic looks like a late ep-3. hmm.

well, any suggestions as to the next step are very welcomed.

best to all,
Jeff Foster ( Oakland CA)

[Enzo]

Here is a place to start:
Regis's Echoplex Page

[spgjmf]

thanks enzo,
yeah I have read the info there, I have all the docs and schematics. right now it appears I have an open record and playback head. both read )0ohms on the meter, while the erase head reads 29ohms.... I am next going to test the recovery amp and make sure its work correctly. inpout amp seems good - I get a nice direct signal...

I wish the ep-4 schematic had voltages and test point like the ep-3. I measures 24 volts, which is correct, but I don't know what the voltage to the bias osc board should be ( the one next to the motor? I get 3 volts on the red wire. I'll try a test tone on the play back lugs and see if I get out put. any one know where to test for voltages or other points, let me know...

I'll check back for updates....

thanks for any suggestions

Jeff