Dynatron cavalcade music centre (SRX30D). Broken switch

[indigo.girl]

Hi everyone,
I have a tape recorder unit that is integrated into a Dynatron cavalcade music centre (SRX30D). The on/off switch is broken and will not stay on. I have dissembled the parts to get to the switch and I think I can see where something has snapped off. My question is can I buy a modern switch that would do the job for a replacement. If not is it OK to bypass the switch so power goes to tape recorder when the music centre is switched on. I can't see how the separate tape recorder switch is required because nothing works until the stop / play / FF buttons etc are pressed.

Many thanks,
Nicola

[Nickthedentist]

Have a look at TV mains switches. There used to be a massive range of replacements available by companies such as Lorlin. May be available NOS.

is it OK to bypass the switch so power goes to tape recorder when the music centre is switched on

Yes, it will be no problem, just a small increase in power consumption.

[Michael Maurice]

I think the reason for the power switch in the first place was because the recorder was available as a stand alone unit for which there needed to be a power switch.

Dynatron would have bought these minus the case and without labels so they could fit their own.

[indigo.girl]

I decided to just connect the wires and remove the switch - it was fairly hidden so doesn't really matter that its gone.

I did a quick test last night and play and stop button work but I don't seem to have any sound or FF or REW. Is there a useful sticky anywhere that I can read that covers the basics of tape recorder function and repair? First time I've tackled one of these.

Thanks,
Nicola

[ms660]

You say the play and stop buttons work, do the cassette spools revolve when the play button is engaged?

Lawrence.

[indigo.girl]

Yes, I can see them rotate when I press play. Nothing happens for REW or FF

[ms660]

It's lots of moons ago since I worked on cassette decks, 40 years plus but check any belts/idlers etc, wish I could be more specific, the rest of the gang might have a better idea, I'm sure it's fixable.

Lawrence.

[indigo.girl]

I've removed some of the circuit boards and can now see the assembly of pulleys that work the mechanics of the tape recorder. One belt is very slack and I suspect has fallen off one or more pulley wheels. Can anyone tell me how they should be joined? At the moment D (the wheel that is attached to the spindle that sit inside the cassette and moves the tape round) is not linked to the motor in anyway.

[ms660]

So far as I can make out the belt that's hung over pulley E and D is the tape counter drive belt, I think I'm right in saying that it should fit into the pulley grooves of those two pulleys, they had a habit of stretching back in the day, that belt shouldn't affect the operation of the FF or RW functions, in fact if it's too loose you can remove it until a replacement is found, it will only mean that the tape counter on the topside of the deck won't function.

The flywheel/capstan drive belt (routed around the motor pulley) appears to be routed correctly so far as I can see, the flywheel is the large rotating metal lump to the left, attached to it topside of the deck is the capstan spindle, that spindle pinches the tape along with the pinch roller, the pinch roller is located top side, the capstan spindle and the pinch roller govern the tape speed when recording and playing back, the flywheel due to it's mass evens out any speed fluctuations that might otherwise occur if a flywheel was not present.

I still haven't figured out the FF and RW mechanism but as said earlier it's been a long time since I worked on such things.

It might help if you could take another photo with a larger view so that all the deck can be seen underneath.

I think there should be another belt somewhere apart from the two mentioned above.

Lawrence.

[Michael Maurice]

There is a small belt that goes where I have (crudely) drawn

[indigo.girl]

Thanks Lawrence and Michael for your comments. So in fact the counter belt is just stretched rather than having fallen off an extra wheel. It looks pretty useless so I might just remove it and live with no counter.

As for the missing belt that goes round B and C I am presuming this has perished. A little detective work and I think I have identified its remains. A black oily smear on the bottom of the wooden cabinet

Attachment 134749

Where can I get a replacement? How important is the tension? Could I use something as crude as an elastic band of a similar size?

Are wheels B and C to do with REW and FF Michael?

Many thanks,
Nicola

[ms660]

This is a very similar Philips mechanism as yours Nicola:

https://www.youtube.com/watch?v=IyChbI29gMU

In the video you will see the operation of wheels B & C that you've referred to.

Lawrence.

[indigo.girl]

You're a star Lawrence - that video is great. I've ordered myself a stash of new belts

[ms660]

Here's hoping what you've ordered are the right ones, the bloke in the video shows that he levered up the bottom flywheel bearing plate in order to slip the belt under, bit of a trick, you might be ok with doing that, that's up to you, I used to remove the plate in order to route the belt around the flywheel, the plate is usually fixed to the chassis with a couple of screws, sometimes the screw holes in the plate were elongated in order to set any end thrust, if you decided to go with the plate removal route then before removing move the flywheel up and down to see and get an approximate feel for any end thrust, any end thrust should be small, if excessive then the bottom bearing surfaces might be partly worn but that's not usually cause for concern, just make sure the end thrust is small when re assembled, don't lubricate the capstan shaft bearing either if re inserting the flywheel if you've decided to remove it for whatever reason, best to do that from the top side, just a small drop or two of light machine oil on the end of a fine screwdriver and apply to the shaft/bearing interface where the shaft protrudes from the bearing, if the tape heads need cleaning then use some IPA on a cotton bud...Heads need to be clean, as does the pinch roller and capstan shaft, if cleaning the capstan shaft don't let it get soaked with IPA as it might run down the shaft into the bearing and thin out the bearing lubricant, put some IPA on cotton bud or lint free cloth and squeeze any excess IPA out so the bud or cloth is just damp.

EDIT: A suitable syringe is good for applying thin lubricants in small quantities into awkward places...more control.

Lawrence.

[ben]

While you're in there, give idlers B/C a going-over with fine sandpaper or you may find the wind speed is poor at start or end of tape.
Also be sure to remove all traces of any black gunk from the pulley indents. Toothpicks are handy for this!

[Jimmyhaflinger]

Originally Posted by pwdrive

Here's hoping what you've ordered are the right ones, the bloke in the video shows that he levered up the bottom flywheel bearing plate in order to slip the belt under, bit of a trick, you might be ok with doing that, that's up to you

Be sure to clean any grease that may contaminate the belt while you slip it under the plate with alcohol or it may cause the belt to deteriorate over time