Restoration of Marconiphone tape recorder.

[goldenfleece]

Just working on this machine, dating from about 1966 I think. This deck was branded as Marconiphone, Ferguson as well as HMV at the time. Semi-functional when I received it, ground to a halt at slowest speed, and lots pitch variation on middle speed but top speed was stable. No tape counter movement, crackly rotary controls, and no playback on two of the four tracks, just a buzzing hum. No recording inputs picked up at all but playback OK.

Simple fix to hum, wire broken from playback head on two track sets, that sorted it.
Noticed a rubber band had been attached to the tape counter drive, which was stuck and just stuttering the supply reel, causing a lot of wow and flutter on playback and no movement at slowest speed. Removed the offending rubber band, pitch variation now gone. Slowest speed was still stationary, no torque at all so decided to clean the main metal drive with next in line with rubber wheel. Problem sorted as a fair bit of grease came off which was preventing torque at low speed.

Rewind and FF all fine and strong, playback now perfect on all three speeds and all four tracks good. Crackly controls cleaned up and all perfect now

But recording, hmmm, nothing at all from microphone, radio IN and AUX din sockets. Have to look at this tomorrow, any ideas what could block every input to record? Erase head working fine, but records nothing, and no monitor sound from input channels either.

No visible signs of electrical problems, but not gone through it all yet in depth.

Is it still possible to get tape counter drive belts for these decks? The rubber band on it was hilarious, far too tight and thick

[AndiiT]

Originally Posted by goldenfleece

.....any ideas what could block every input to record?....

Hi, check the output valve screen grid decoupling capacitor, usually around 16 to 32 uF and often housed in a can with the main smoothing capacitor and output valve cathode bypass capacitor, to be fair these will probably also need replacing anyway.

These machines use the output valve as the Erase/Bias oscillator on record (as is the case with many machines of this type) and a failed/low capacitance screen grid decoupler will cause recording issues.

Regards

Andrew

[dazzlevision]

The photo in post 1 shows a Thorn DC43 deck and the electronics uses a separate bias oscillator valve (ECC82).

[dazzlevision]

If the recorder is totally "dead" in record mode, but works normally in playback mode, I would firstly check that the mechanical linkage from the red record key to the slider switch on the printed circuit board is operating correctly.

If it is, then it's surprising there is no output from the speaker when you connect an input to any of the input sockets (MIC, Radio, PU and PU2).

The crystal microphone that was supplied with this recorder may well be faulty now, giving no output at all.

Do not leave it plugged into the MIC socket whilst testing the other input sockets at the rear of the recorder (RADIO and PU2), as they are automatically disconnected when a mike is plugged in (apart from the "PU" DIN socket).

[goldenfleece]

I don't seem to have the original microphone. Further investigations will follow, as it is possible my current one and only DIN lead is faulty

[dazzlevision]

Originally Posted by goldenfleece

I don't seem to have the original microphone. Further investigations will follow, as it is possible my current one and only DIN lead is faulty

Do a simple hum test. With the machine set to record and with pause key pressed, set both record level controls to maximum and volume to mid range setting. If you press a finger onto the MIC socket, you should hear a 50 Hertz hum, which will get a lot louder if you actually insert a short length of bare thin solid core wire (or a very small screwdriver) into pin 2 or 4 of the MIC socket (these have the two visible metal contacts that are separated when the microphone is plugged in).

Alternatively, in record mode and with all rotary controls fully clockwise and speed set to slowest, you should hear a distinct hiss and some hum from the speaker. This will give a good indication that the record amplifier is working, if not the bias oscillator. You can test if the bias oscillator is working by trying to erase a short section of a previously recorded tape - if you have one.

[goldenfleece]

yes deffo got a loud buzz/hum when touching the mic and LINE sockets, so that's a good sign. Also tapes are being erased fine, I think I must just have a dodgy DIN lead.....