Sunday, November 23, 2014

Unpacking a new mainspring

Waiting for the new rubber grommets as feet for the #2 Portable. What did however arrive in the meantime was a new mainspring for the HMV102 portable gramophone.

A couple of months ago it started to have trouble keeping speed. At first only on some louder passages, but then on any record. Even after re-greasing the spring it was painful to listen to the false notes as the motor struggled and failed to keep speed. This meant that probably the mainspring was just spent and needed replacing.

Luckily and amazingly newly manufactured mainsprings are readily available, so an order was placed and duly received. It arrives tightly wound and held by a steel wire.


Unpacking a new mainspring is a bit tricky. To contain the force of the spring uncoiling and prevent the inch-wide steel spring from inflicting injury, it was first wrapped in a rag. With the spring in the rag the steel wire was cut, immediately followed by a roar and rumble as the spring expands against the rag. Slowly releasing the rag then gives a controlled uncoiling of the new mainspring (without injury).


For the HMV102, disassembly and taking out the spring is very clearly and helpfully described at a blogpost at Project Repair. Following those steps, the old spring was taken out again. Ultimately the new mainspring needs to be packed tightly again into this drum, but first it needs to be greased all over. Then its end needs to be hooked over the peg inside the drum wall. Can be done but the new straight spring makes this harder than it was with the old one.

Re-packing the new spring into the drum made clear that the old spring was spent. The new spring put up much more of a fight over being forced into the drum than the old spring. Again: do NOT let go of it when halfway.


Going through the steps in reverse order assembles the whole thing again. Hardest step is fitting the drum back on the centre shaft again, this is a very tight fit and the new spring centre hole does not centre over the drum opening. Several tries and some tweaking gets it back on however.

With the new mainspring fitted the HMV102 now keeps speed again.

Analog and fixable machines :)

2 comments:

  1. Where did you acquire said mainspring?

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    Replies
    1. Got it from De Zwarte Schijf (www.zwarteschijf.nl).

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