Does the teletype print correctly in local mode? Could it be a problem with the receive mechanciam in the Model 33? Can you correctly read charactes from the Model 33 keyboard on the PDP11? If you can't get hat working, you'll almost certainly havve problems with the reader too, the serialiser is the same device (the rotating 'distributor' at the rear right corner of the Model 33 tpying unit. But anyway, let's get the reader working too... Let's being with how the reader control should work. There's a little electromagnet (the 'trip coil') on top of the typing unit at the rear right side. When it is energised, it releases the trip lever. This engages the transmit clutch and the distributor disk rotates. It also closes the little switch contacts just in front of the trip coil (black and wihite wires with faston terminals IIRC). This then energises the larger solenoind in the reader itself, causign the sense pins ('peckers', at least over here) to rea the tape. The electical outputs from the switch contacts operated by the sense pins are serialised by the distributor contact. At theend of the character (one revolution of the transmit shaft), the trip lever is mechancially restored by a cam on the shaft. This opens the contacts, de-energising the reader soloid, which lowers the sense pins and advnces the tape for the next character. If the trip coil is still nergised, the trip lever is not latched at this point, and the cycle repeats, reading successive chracters from the tape. If the trip coil is deenergised, then at the end of the current caracter, the trip lever is latched in the idle position, disengaging the transmit clutch (and stopping the distributor) and holding the contacts open so that the reader soleoid is not energised. The power fro the reader solenoid comes from a PSU module that is often mounted in the stnad. Note that this is not isolated from the mains (power line) But there;'s no need to modify the wiring in that part of the circuit. The trip coil is pweered from an isolated (mains transformer) supply in the call control unit. All reader control is done through this coil. The orioginal wiring was to simply connect the reader on/off switch and tape-out contacts (in the reater itself) in series with this coil. When the reader switch was turned on, the trip coil was energised, and the reader read the tape as I've just descibed. There was an 'official' Teletpye versio nwith automatic reder control. This detected 2 control chreactters using levers in the 'stunt box' under the platen. These operated swithc contacts (there may well have been a latching relay involved too) to control the trip coil circuit. This version is not at all common (at least not over here). However, most computer manufcaters had their own modification which involved adding a relay contact to the trip coil circuit. The relay coil was controlled by the computer interface. The idea was that the computer could turn on the trip coil, then when the first bit of the chracter was received, the trip coil was denergised. Of course this meant the reader would stop after the chracter and wait for the computer to request the next one. It basically gave a single-stip control of the reader. Althoug hthis was not an official Teletype modification, it appears that most computer manufacturrs did it in essentially the same way. The modifications used by DEC, Intel and HP are all much the same. The first thing I would do is have the machine running in Local mode with the covers off and a piece of tape in the reader. Press down the armature flap on top of the trip coil. If the reader now runs (and the tape cotnents are printed out on the Model 33), then the reader and the mechancial side of things ae all working properly, and any problems are in the trip coil circuit (most likely) Could this be a relay (possiblty a reed relay or even a mercury-wetted relay), not a transformer? It would be conventional to put the contacts in sieres with the trip coil circuit and feed the coil connections out fo the machine and back to the computer. I would invetigate thsi some more. What is the DC resistance between the 2 connections that go to the reader circuit (with those wires disconnected from the rest of the teletpye)? If inifinite, this does suggest a relay contact. Does anyhting happen if you apply 24V (or so) between the 2 wires coming out of the machien from thsi device? If the resistance drops to 'very low' then it really does sound like a relay. Reconnect it, Apply 24V, and see if the reader runs now. No. The high pseed reader is totally different thing, with its own (parallel) interface. The DEC connecotr has 6 pins used, 2 each for the transmit currnet loop, receive current loop and reader run relay. The last will drive a small relay coil directly. Has this Model 33 ever been used on a PDP11? If so, it's likely to be vertsion of the normal DEC modification and you can just connct up the relay coil wires to the 2 remaining pins on the mate-n-lock. -tony