UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio and TV Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > Specific Vintage Equipment > Vintage Audio (record players, hi-fi etc)

Notices

Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment.

Reply
 
Thread Tools
Old 2nd Apr 2024, 11:13 pm   #1
evendine
Triode
 
Join Date: Nov 2019
Location: Malvern, Worcestershire, UK.
Posts: 17
Default Garrard AC-7A Deck Issues...

Wonder if anyone might advise me on the best way to resolve a bearing alignment issue with a Garrard AC-7A motor + identify / setup the Garrard(?) tonearm and its HMV moving magnet cartridge.

As I'm sure many know, the motor design dates from 1928 and is 78RPM only, but it came with a set of interesting records including 'Rock Around The Clock', so quite keen to get it running again :0)

It arrived as part of a military style metal cased radiogram, so may have been used during WWII. This is the nearest reference to it I've been able to find online, although this example has a different cartridge:

https://www.youtube.com/watch?v=FAUpsxOwYL0

Essentially, the output shaft end seems out of line with the stator end. Have cleaned all bearing surfaces and re-oiled / re-greased, but won't turn freely when inserted into the sintered brass bearing, although it does otherwise. Looking along the line of the output shaft, it seems that it's lower than it needs to be. The unit wasn't well packed, so may have suffered a drop in the post which caused the stator casing to move, perhaps?

Any thoughts on the arm / cartridge also much appreciated!
Attached Thumbnails
Click image for larger version

Name:	20240321_135759.jpg
Views:	59
Size:	82.3 KB
ID:	295766   Click image for larger version

Name:	20240322_181448.jpg
Views:	81
Size:	75.1 KB
ID:	295767   Click image for larger version

Name:	20240323_203051.jpg
Views:	62
Size:	49.7 KB
ID:	295768   Click image for larger version

Name:	20240323_233423.jpg
Views:	52
Size:	48.8 KB
ID:	295769   Click image for larger version

Name:	20240324_231554.jpg
Views:	46
Size:	37.7 KB
ID:	295770  

evendine is offline   Reply With Quote
Old 3rd Apr 2024, 10:39 am   #2
Analogue man
Hexode
 
Join Date: Dec 2020
Location: Raunds, Northamptonshire, UK.
Posts: 354
Default Re: Garrard AC-7A Deck Issues...

I don't know anything about this motor but it looks to me that the shaft is not engaging with the bearing in the governor housing and there appears to be an end cap to the bearing at the other end of the motor, I would suggest that this is where you should start as possibly the bearing may have fallen apart or have a component missing.
__________________
Graham
Analogue man is offline   Reply With Quote
Old 3rd Apr 2024, 3:07 pm   #3
evendine
Triode
 
Join Date: Nov 2019
Location: Malvern, Worcestershire, UK.
Posts: 17
Default Re: Garrard AC-7A Deck Issues...

Hi Graham,

thanks for your reply. When I stand the motor up vertically on the electrics block with the brass bearing in the governor housing removed, the shaft with its mechanical governor rotates freely. Have removed and regreased the plate with its endcap at the electrics block end and it seems to be in proper contact with that end of the shaft.

When the other end of the shaft (away from electrics block) is engaged with the bearing in the governor housing, free rotation stops, so seems the shaft is out of alignment. Certainly looks to be out of vertical alignment as you may be able to see from the pic above taken through the governor housing with the brass bearing removed.

Have read here that it's best not to disturb the electrics block unless necessary, but would seem this might be the only way to realign the shaft. This is my first attempt to restore such a motor, so appreciate any advice

Thanks again

Martin

ps: seems the AC6 and AC7's are very similar, so I've attached the only diagram i could find below...
Attached Thumbnails
Click image for larger version

Name:	garrard-philips-ac6-1938.jpg
Views:	31
Size:	65.3 KB
ID:	295788  
evendine is offline   Reply With Quote
Old 3rd Apr 2024, 8:40 pm   #4
Yarraman
Tetrode
 
Yarraman's Avatar
 
Join Date: May 2007
Location: Auckland, New Zealand
Posts: 85
Default Re: Garrard AC-7A Deck Issues...

I too will be interested in any replies for the AC 7A motor, i have one that doesn't rotate. Even when cleaned up and the shaft appears free enough. It hums when power is connected, but still wont start even when i try to rotate it. The Stator winding measures 814 Ohms.
Yarraman is offline   Reply With Quote
Old 3rd Apr 2024, 11:14 pm   #5
evendine
Triode
 
Join Date: Nov 2019
Location: Malvern, Worcestershire, UK.
Posts: 17
Default Re: Garrard AC-7A Deck Issues...

My stator winding measures 770R for reference, so not a great difference. Mine also hums when I did a brief test with the governor case bearing and the shaft in place.

Surprised that the motor won't turn when you have free rotation. Don't think these have brushes of any sort. Does the shaft turn noticeably more freely when you remove the brass bearing in the governor housing and stand the motor on the electrical block end?
__________________
Martin
evendine is offline   Reply With Quote
Old 3rd Apr 2024, 11:44 pm   #6
Analogue man
Hexode
 
Join Date: Dec 2020
Location: Raunds, Northamptonshire, UK.
Posts: 354
Default Re: Garrard AC-7A Deck Issues...

I'm not sure if the following will work but it might just be worth a try. The service sheet for a Collaro 3RC531 states that if the motor bearings are dragging then remove the motor from the deck, power it up and gently tap the end opposite to the visible shaft on all sides. This is supposed to shock the bearing back into alignment. I've tried this on various motors with complete 100% success.
__________________
Graham
Analogue man is offline   Reply With Quote
Old 4th Apr 2024, 8:40 pm   #7
Yarraman
Tetrode
 
Yarraman's Avatar
 
Join Date: May 2007
Location: Auckland, New Zealand
Posts: 85
Default Re: Garrard AC-7A Deck Issues...

My AC 7a won't run even on its end, I applied power and the shaft actually "freezes" so there is magnetism produced from the stator winding, it just won't spin. There must be something wrong with the "shaded pole windings"? although they look intact and in their places. when I remove the power, the shaft can spin freely with my fingers.
Yarraman is offline   Reply With Quote
Old 4th Apr 2024, 9:18 pm   #8
Yarraman
Tetrode
 
Yarraman's Avatar
 
Join Date: May 2007
Location: Auckland, New Zealand
Posts: 85
Default Re: Garrard AC-7A Deck Issues...

I suspect the shaded pole windings (copper) are suppose to be insulated? probably with varnish in the 1930's and that insulation has broken down? hopefully, someone can confirm this or not ?
Yarraman is offline   Reply With Quote
Old 4th Apr 2024, 9:27 pm   #9
Yarraman
Tetrode
 
Yarraman's Avatar
 
Join Date: May 2007
Location: Auckland, New Zealand
Posts: 85
Default Re: Garrard AC-7A Deck Issues...

Quote:
Surprised that the motor won't turn when you have free rotation. Don't think these have brushes of any sort. Does the shaft turn noticeably more freely when you remove the brass bearing in the governor housing and stand the motor on the electrical block end?

They don't have brushes, they are an induction motor which have "Shaded pole" windings to shift the phase so that the motor starts rotating. some induction motors have a capacitor to shift the phase, but these use 4 bands of copper around the stator.
Yarraman is offline   Reply With Quote
Old 6th Apr 2024, 9:53 pm   #10
Yarraman
Tetrode
 
Yarraman's Avatar
 
Join Date: May 2007
Location: Auckland, New Zealand
Posts: 85
Default Re: Garrard AC-7A Deck Issues...

I found this description on the internet and I'm sure it's the reason my AC 7a motor isnt spinning.

"When the rotor bars of an induction motor become shorted, it can result in several issues with the motor's performance. Shorted rotor bars are caused by insulation breakdown, which can occur due to aging or overheating of the motor.

One of the primary effects of shorted rotor bars is an increase in rotor resistance, which reduces the motor's efficiency and can cause it to overheat. This is because the shorted rotor bars create a high resistance path that limits the flow of current through the motor. As a result, the motor draws more current to compensate for the reduced voltage, causing it to overheat.

Another effect of shorted rotor bars is increased noise and vibration in the motor. The shorted bars cause an imbalance in the rotor, which can lead to increased mechanical stress and wear on the motor's bearings. This can result in increased noise and vibration levels, as well as reduced motor lifespan.

In some cases, shorted rotor bars can also cause the motor to stop working altogether. This is because the shorted bars can cause the motor to draw too much current, which can trip the motor's protective circuits and cause it to shut down.

To prevent shorted rotor bars, regular maintenance and testing of the motor is necessary. This can include regular inspections of the motor's insulation, as well as testing the motor's resistance and current draw to detect any abnormalities."
Yarraman is offline   Reply With Quote
Old 7th Apr 2024, 4:09 am   #11
Yarraman
Tetrode
 
Yarraman's Avatar
 
Join Date: May 2007
Location: Auckland, New Zealand
Posts: 85
Default Re: Garrard AC-7A Deck Issues...

Today I've managed to clean out the metal shorts between the rotor bars on the rotor and now the motor actually rotates by itself, so years of wear on the rotor had metal filings filling up the gaps between the rotor bars. The motor is a little noisy, the bearing are most likely worn too, but I've learnt something.
Getting the motor end cap back in the right position so the rotor rotates effortlessly was a mission too.
Attached Thumbnails
Click image for larger version

Name:	Garrard AC 7a squirrel cage rotor.jpg
Views:	27
Size:	32.5 KB
ID:	295938  
Yarraman is offline   Reply With Quote
Old 20th Apr 2024, 3:05 pm   #12
evendine
Triode
 
Join Date: Nov 2019
Location: Malvern, Worcestershire, UK.
Posts: 17
Default Re: Garrard AC-7A Deck Issues...

Removed the stator winding end housing and looks as though one of the "Shaded Pole" bars was shorted to case (i.e. earth), some insulation is missing on one stator feed wire and the shaft is out of alignment. Looks as though someone has tried to repair the unit in the past without success.

Think i can correct the electrical issues, but as you say Yarraman, quite a job to get everything back in place. Any tips on how you managed to reassemble it?
__________________
Martin
evendine is offline   Reply With Quote
Reply

Thread Tools



All times are GMT +1. The time now is 8:04 pm.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Copyright ©2002 - 2023, Paul Stenning.