Troubleshooting help - Ampex 351-2 won't go into Record

IronWine

Member
Hey guys
I've spent the last few months refurbishing 351-2 model made by Ampex. many hours have been put into it , including refurbishing the transport, recapping, replacing bad R's and cleaning it down to the screw..

This week I finally assembled it all, starting testing it out. The preamps exhibits good in's and out's and nice headroom. the machine playback tapes nicely. Unfortunately I am unable to engage the record mode on both preamps. tape is spinning, but not recording..


Schematics suggests that the K-1 Relay that sits on the power supply pcb suppose to be engaged when I hit the record, but no 'click' sound or any life sign from the relays. I doubt that both relays had gone bad and they both shows good resistance. I was unable to locate any shorts in the circuits.

I assume that the signal that suppose to "inform" the relays that the transport is playing is not making it's way to the preamps.
I think next step is to disassemble the Control Circuit board of the transport..

any suggestions? may I have missed something? had any one refurbished that machine and can give some input?

thanks!
 
When you try to engage REC, hold the REC button and measure the voltage at the coil of the relay. I believe it should be close to +24V.

Dont just start disassembling stuff. I’m not familiar with the 35x machines at all...don’t have a manual handy. You have one, yes? If there is a Theory of Operation section, read that. It should walk you through exactly what happens when you press that record button, down to identifying the components that respond and how and why. That will give you all sorts of suggestions of things to test. You just follow the narrative theory of how it’s supposed to work...follow along and when it say x does y you test and make sure that is happening. That should identify the problem. But yes it could be no power is reaching the relay coils in order to latch the relay contacts, or the voltage is too low to power the relay coil enough to close the contacts and latch the relay.
 
Ooo! Nasty.

Not related but another observation? I see 12AX7 and 12AU7 in there, do not get them mixed. the U7 position will likely bugger an AX in short order. A 12AU7 will likely burn out AX components.
I dare say on gear of that quality the valve positions are marked on the chassis? If not get the Dymo out.

Best of,
Dave.
 
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