Echoplex EP3 won't record

[Tech. Tom]

Hello:
I am trying to fix this unit. I have never worked on one before.
I can get a signal through it but there is no echo. All I have is a new blank tape
so I put a signal generator probe near the playback head and I get a signal through it.

I originally found 2 electrolytic capacitors wide open so I changed them and 5 others
for good measure. All the heads read ok resistance wise. The schematic calls for 37VP-P
and I only had 13VP-P so I adjusted the bias and now it is correct. The manual says the
frequency is 100KHZ but I read 72KHZ. I don't know if that's a problem or not.

All DC voltages on transistors read good except Q4. It calls for 14.3 on the collector and I have
13V. It calls for 2.2V on the base and I have 2.6V. The emitter calls for 16V and I have 2 volts.

I changed the transistor even though it checked ok.
I have attached the schematic.


Thank you.
Tom

[52 Bill]

All DC voltages on transistors read good except Q4. It calls for 14.3 on the collector and I have 13V. It calls for 2.2V on the base and I have 2.6V. The emitter calls for 16V and I have 2 volts.

Have you tested the components connected to the emitter of Q4?

If you send an audio signal into the input can you trace it through Q3 and Q4 to the record head?

There are specific directions on how to adjust the bias trimmers. They are all based upon signal levels and not so much in voltage readings. Once you get it working, I'd suggest that you reset the trimmers to match the specs.

[km6xz]

When you say you get signal through it, you are talking about dry signal but no recovery from the head at all?
I would not bother with voltage measurements yet, but signal path. Isolate whether the fault is in the record amp/head or repro head. Don't measure the head windings with an ohm meter unless you know it sources very little current. The wire inside the head can be burned by a DC current from the ohmmeter.
When you say it is a new tape, original or a repack. If the latter the simplest cause of the problem could be the tape is backing against the head. Cart tape is different than reel tape, cart tape is what is needed since it has lubricant to allow the supply reel to also be the take up reel by pulling the tape from the interior of the tape pack against the hub, and the outer wrap is the take up return.. To do that reliably it has lube on both sides of the tape. Cart tape was usually low flux type, less than 185 nanoweber/m^2 and later reel audio tape was high flux density 250-385nw/m^2. It is not going to record if the tape is flipped. Do you see the audio modulating the bias using a scope probe on the record head? You should see a clean signal with little bias signal when viewing the collector of Q4.