Dynacord Echocord tape delay restoration. Help with motor circuit debug

[beatnik]

Hi everybody

I am restoring an old Dynacord tube tape delay, model Super 62

First thing I have replaced the electrolytics and after initial power up I could get the right voltages out of the power transformer, but the motor doesn't run

The motor has two speed settings which can be selected via switches on the front panel. I have cleaned these with deoxit and tested the contacts, they are fine

The motor has six wires. I have desoldered these from the circuit and tested the terminals for resistance. There aren't any open circuits, and all terminals have a range of 30-50 ohm resistance between each other.

I don't know much about motors, does this look correct to you ? I have attached a schematic which doesn't show the internal winding configuration of the motor, but this is the only documentation i could find

If the motor itself is ok, my only suspect at this point would be the motor start capacitor.

Is there any way I can test the motor without connecting it to the rest of the circuit ?

 

[PRR]

> motor doesn't run

Motor does not START to run.

What if you chuck it in the drill and spin it, while feeding the windings? Many AC motors will not self-start without tricks (caps), but will keep spinning if brought up to line speed.

> my only suspect at this point would be the motor start capacitor.

You have switch. You have windings (BTW it appears to be "two 3-wire motors" on one frame). I ass-ume you have 42VAC. What is left? What is notorious for crapping out on a hot day (at least in air-conditioners)? Get a new start cap.

(This is probably a "run" cap which is also needed to start. But you don't have to know that to replace it.)

 

[beatnik]

thanks for your reply PRR

i have been trying to find a suitable replacement cap and - please correct me if i'm wrong - it appears there is a distinction between "start" and "run" types

this one for example is specific for motor start and the description says it shouldn't be used for run application

http://www.ebay.co.uk/itm/40-50uF-40-50mfd-Motor-Start-Capacitor-220-275Vac-/162443287172?hash=item25d25fda84:g:agAAAOSwXYtY2Ph5

I was trying to find one that matches the diameter of the original cap, so I can fit it in the existing bracket. This one would fit perfectly but the datasheet says once the motor is started, the cap must be disconnected from the circuit

http://www.ebay.co.uk/itm/4-12-80-3-406-Capacitor-for-motors-start-50uF-250V-36-5x68-5mm-/192077490367?hash=item2cb8b5e8bf:g:lgIAAOSwjDZYeNmg

http://www.tme.eu/gb/Document/e178678d57c059405f76656e52d2a0b1/start_capacitors_v1.pdf

i don't know if i am just over thinking  this but it seems that the cap stays in circuit so maybe this is not the correct type ?

 

[moamps]

IMO, you need a motor run capacitor. Like this one
http://www.ebay.ie/itm/Motor-run-capacitor-bipolar-f-Echolette-48MFD-100VAC-FTCap-AskJanFirst-/252693488433?hash=item3ad5b4a331:g:8ggAAOSw2GlXG6nJ

 

[PRR]

Historically, start caps are larger and only work a few seconds per start, a few hours a decade. Run caps tend to be smaller uFd, bigger cases, work full time. A "run" cap is safer when you do not know. (It is *possible* there is a throwout switch inside the motor. Had a pump was that way.)

 

[DerEber]

Look at the second cap on this page.
Maybe it is the one you need:

http://die-wuestens.de/eindex.htm

best,
Stephan

 

[beatnik]

that seems to be exactly what the doctor ordered

thanks !

 

[radardoug]

If your motor hasn't been used in a while, the first thing I would do is clean and lube the bearings, and make sure that the motor turns freely.

 

[saint gillis]

Some brilliant information about the motor here :