Overheating Motek K9/RGD mono tape recorder. - UK Vintage Radio Repair and Restoration Discussion Forum

johnny english · 5th Oct 2015, 9:15 pm

I have been working on this machine for weeks and no further forward. I down loaded the regentone rt51 (which is the same machine) service data from vrsd but I am totally bewildered.
The heat generated by the machine is quite hot each motor, of which there are three, generate a lot of heat. I removed each motor and stripped down and relubed thinking that would be the solution, the same problem remained. I then checked the the power supply and mains dropper along with the main capacitors. The tape path was cleaned and the guides polished up and the tape runs smoothly. When the tape starts it plays at the correct speed 7.5ips and after about 10-15 minutes it starts to slow down. The tape I use is maxell and there is no shedding of oxide to clog things up. I have also regreased the capstan and the idler wheel is in perfect condition.

Restoration73 · 6th Oct 2015, 8:35 am

Shaded pole motors are inefficient in terms of heat loss and this is normal - the take
up spool motor may run a bit cooler in play and record as it is run in series with a 1k
resistor. Some motor manufacturers extended the spindles and fitted fan blades to
enhance cooling. Just ensure ventilation is adequate.

johnny english · 6th Oct 2015, 2:21 pm

Thanks for your advice.
I had this morning free and followed your suggestion of ensuring adequate ventilation. I removed the base ventilation grill and added another inch of height under the equipment feet whilst also raising the deck half an inch, the result was the machine ran much cooler but the same symptoms resumed. Perhaps its time to call it quits which is a shame really as its a pretty solid machine and the tape heads were functioning well. At least with the help from
members on the forum I was able to give it my best shot,

Thanks Ed.

vidjoman · 6th Oct 2015, 4:24 pm

Is the idler wheel drive between the motor and flywheel good. If it's hardened it will probably slip and the tape will slow down.

johnny english · 6th Oct 2015, 5:01 pm

The rubbers hard but is still pliable, it runs straight and true and is very grippy as the expansion spring for the pulley wheel still has a strong pull.

dseymo1 · 6th Oct 2015, 5:04 pm

When it slows down, is the capstan motor still perfectly free to rotate?

johnny english · 6th Oct 2015, 7:06 pm

The capstan revolves via the rubber pulley/idler wheel which engages the stepped pulley of the motor.
The capstan motor and the take up reel both turn freely with no humming or buzzing and the recording tape runs
perfectly. The effect is like you are listening to a walkman and the batteries are running out.

dseymo1 · 6th Oct 2015, 8:08 pm

If it were mine, I'd make a little strobe disc to fit the capstan motor shaft, and run it until the fault occurred. This would then point the finger at either the motor or the drivetrain.

johnny english · 7th Oct 2015, 2:38 pm

Thanks everyone for your responses it cheered me up and has resolved my determination to try and fix the problem. I think it may possibly have something to do with the capstan bearings. The capstan is a heavy big lump of brass with a ball bearing cupped into the top end which engages into the top support there is no sign of wear so the capstan runs very smoothly. The base has a steel bearing shaped like a cone which runs against the end of an adjustment bolt. This arrangement has the full weight of the capstan supported by the smallest possible contact point. I will post some photos later showing the set up.

johnny english · 15th Oct 2015, 10:42 pm

It,s been a while but it looks like the pulley wheel rubber is the problem. I abraded the wheel with 1000 w/dry which removed the shine to reveal the original rubber but after 10 minutes of playing it started getting shiny again so it looks like a refurb is the order of things. Quite a few posts on the forum recommend Terry,s Rubber Rollers and parts in the USA. I was wondering if their was anyone in the UK who provide a similar service.

Thanks Ed

ricard · 21st Oct 2015, 9:11 pm

You might also try the type of rubber cleaner intended for printers (often labeled 'printer platen cleaner' or similar). These seem to be able to clean the surface and restore friction. There used to be a product from KontaktChemie in Germany called Gummi-Reiniger GR, but I think it is no longer made.

johnny english · 22nd Oct 2015, 12:04 am

Thank you Ricard.
I will try and find a can and try it out. I am also considering gluing an O ring to the wheel hoping this method may provide the extra grip.

johnny english · 7th Nov 2015, 12:41 am

Been having a few problems with a motek k9 tape recorder deck. I have finally managed to get it playing at the correct speeds. All voltages are within spec but the capstan motor which has a fan for cooling will reach a temperature of 75d centigrade when the deck is fitted to its cabinet, with the deck raised up by a few inches the temperature drops to 65d centigrade. Temp readings taken after about an hours use. I know that the heat can be expected with a shaded pole motor but 75d seems a bit excessive. besides providing extra ventilation would a specific lubricating oil for this type of motor be advisible and if so what type. I used castrol motor oil and the rotor does spin for a few seconds after the power is cut off.

llama · 8th Nov 2015, 10:09 am

From the earlier posts it seems the capstan motor is linked to the capstan/flywheel by an idler wheel. I guess that's spring loaded. Can you run the thing for a while with the idler pulled away from the flywheel? That would isolate just the motor.

Another thought is too much pull-in on the idler. The test above would isolate that, too.
Graham

johnny english · 8th Nov 2015, 2:14 pm

When I increased the tension on the pulley wheel spring it caused the speed to drop further so I eased off and returned it to its original setting. I then decided to strip the capstan motor down even though it was`nt squeaking or rumbling and ran freely.The top bearing was still well lubricated as was the lower one. I had previously lubricated the motor earlier as upon inspection they were quite dry. Purely by chance when looking at the lower bearing I caught a glimpse of a flat spot on the ball bearing housed at the bottom of the sintered bearing which is used as a spacer for the rotor shaft. I popped the bb out and fitted a replacement. Fitted everything back together loaded a tape and pressed play, usually within about ten minutes the speed would drop, 45 minutes later still playing at the correct speed. I ran the machine for three hours with the speed remaining stable. I can only assume that this machine was`nt regularly serviced. Regarding the high temperature of this motor (75c) I raised the deck
by 10mm to aid ventilation the motor temperature has dropped to (73c).

5th Oct 2015, 9:15 pm	#1
johnny english Retired Dormant Member Join Date: Nov 2013 Location: Liverpool, Merseyside, UK. Posts: 160	Overheating Motek K9/RGD mono tape recorder. I have been working on this machine for weeks and no further forward. I down loaded the regentone rt51 (which is the same machine) service data from vrsd but I am totally bewildered. The heat generated by the machine is quite hot each motor, of which there are three, generate a lot of heat. I removed each motor and stripped down and relubed thinking that would be the solution, the same problem remained. I then checked the the power supply and mains dropper along with the main capacitors. The tape path was cleaned and the guides polished up and the tape runs smoothly. When the tape starts it plays at the correct speed 7.5ips and after about 10-15 minutes it starts to slow down. The tape I use is maxell and there is no shedding of oxide to clog things up. I have also regreased the capstan and the idler wheel is in perfect condition. Attached Thumbnails

6th Oct 2015, 8:35 am	#2
Restoration73 Nonode Join Date: Jun 2013 Location: Surbiton, SW London, UK. Posts: 2,801	Re: Overheating Motek K9/RGD mono tape recorder. Shaded pole motors are inefficient in terms of heat loss and this is normal - the take up spool motor may run a bit cooler in play and record as it is run in series with a 1k resistor. Some motor manufacturers extended the spindles and fitted fan blades to enhance cooling. Just ensure ventilation is adequate.

6th Oct 2015, 2:21 pm	#3
johnny english Retired Dormant Member Join Date: Nov 2013 Location: Liverpool, Merseyside, UK. Posts: 160	Re: Overheating Motek K9/RGD mono tape recorder. Thanks for your advice. I had this morning free and followed your suggestion of ensuring adequate ventilation. I removed the base ventilation grill and added another inch of height under the equipment feet whilst also raising the deck half an inch, the result was the machine ran much cooler but the same symptoms resumed. Perhaps its time to call it quits which is a shame really as its a pretty solid machine and the tape heads were functioning well. At least with the help from members on the forum I was able to give it my best shot, Thanks Ed.

6th Oct 2015, 4:24 pm	#4
vidjoman Dekatron Join Date: Jun 2013 Location: East Sussex, UK. Posts: 3,326	Re: Overheating Motek K9/RGD mono tape recorder. Is the idler wheel drive between the motor and flywheel good. If it's hardened it will probably slip and the tape will slow down.

6th Oct 2015, 5:01 pm	#5
johnny english Retired Dormant Member Join Date: Nov 2013 Location: Liverpool, Merseyside, UK. Posts: 160	Re: Overheating Motek K9/RGD mono tape recorder. The rubbers hard but is still pliable, it runs straight and true and is very grippy as the expansion spring for the pulley wheel still has a strong pull.

6th Oct 2015, 5:04 pm	#6
dseymo1 Retired Dormant Member Join Date: Dec 2007 Location: Shropshire, UK. Posts: 3,051	Re: Overheating Motek K9/RGD mono tape recorder. When it slows down, is the capstan motor still perfectly free to rotate?

6th Oct 2015, 7:06 pm	#7
johnny english Retired Dormant Member Join Date: Nov 2013 Location: Liverpool, Merseyside, UK. Posts: 160	Re: Overheating Motek K9/RGD mono tape recorder. The capstan revolves via the rubber pulley/idler wheel which engages the stepped pulley of the motor. The capstan motor and the take up reel both turn freely with no humming or buzzing and the recording tape runs perfectly. The effect is like you are listening to a walkman and the batteries are running out. Last edited by johnny english; 6th Oct 2015 at 7:19 pm. Reason: adding extra information

6th Oct 2015, 8:08 pm	#8
dseymo1 Retired Dormant Member Join Date: Dec 2007 Location: Shropshire, UK. Posts: 3,051	Re: Overheating Motek K9/RGD mono tape recorder. If it were mine, I'd make a little strobe disc to fit the capstan motor shaft, and run it until the fault occurred. This would then point the finger at either the motor or the drivetrain.

7th Oct 2015, 2:38 pm	#9
johnny english Retired Dormant Member Join Date: Nov 2013 Location: Liverpool, Merseyside, UK. Posts: 160	Re: Overheating Motek K9/RGD mono tape recorder. Thanks everyone for your responses it cheered me up and has resolved my determination to try and fix the problem. I think it may possibly have something to do with the capstan bearings. The capstan is a heavy big lump of brass with a ball bearing cupped into the top end which engages into the top support there is no sign of wear so the capstan runs very smoothly. The base has a steel bearing shaped like a cone which runs against the end of an adjustment bolt. This arrangement has the full weight of the capstan supported by the smallest possible contact point. I will post some photos later showing the set up.

15th Oct 2015, 10:42 pm	#10
johnny english Retired Dormant Member Join Date: Nov 2013 Location: Liverpool, Merseyside, UK. Posts: 160	Re: Overheating Motek K9/RGD mono tape recorder. It,s been a while but it looks like the pulley wheel rubber is the problem. I abraded the wheel with 1000 w/dry which removed the shine to reveal the original rubber but after 10 minutes of playing it started getting shiny again so it looks like a refurb is the order of things. Quite a few posts on the forum recommend Terry,s Rubber Rollers and parts in the USA. I was wondering if their was anyone in the UK who provide a similar service. Thanks Ed

21st Oct 2015, 9:11 pm	#11
ricard Octode Join Date: Mar 2006 Location: Lund, Sweden Posts: 1,632	Re: Overheating Motek K9/RGD mono tape recorder. You might also try the type of rubber cleaner intended for printers (often labeled 'printer platen cleaner' or similar). These seem to be able to clean the surface and restore friction. There used to be a product from KontaktChemie in Germany called Gummi-Reiniger GR, but I think it is no longer made.

22nd Oct 2015, 12:04 am	#12
johnny english Retired Dormant Member Join Date: Nov 2013 Location: Liverpool, Merseyside, UK. Posts: 160	Re: Overheating Motek K9/RGD mono tape recorder. Thank you Ricard. I will try and find a can and try it out. I am also considering gluing an O ring to the wheel hoping this method may provide the extra grip.

7th Nov 2015, 12:41 am	#13
johnny english Retired Dormant Member Join Date: Nov 2013 Location: Liverpool, Merseyside, UK. Posts: 160	hot motor problem Been having a few problems with a motek k9 tape recorder deck. I have finally managed to get it playing at the correct speeds. All voltages are within spec but the capstan motor which has a fan for cooling will reach a temperature of 75d centigrade when the deck is fitted to its cabinet, with the deck raised up by a few inches the temperature drops to 65d centigrade. Temp readings taken after about an hours use. I know that the heat can be expected with a shaded pole motor but 75d seems a bit excessive. besides providing extra ventilation would a specific lubricating oil for this type of motor be advisible and if so what type. I used castrol motor oil and the rotor does spin for a few seconds after the power is cut off.

8th Nov 2015, 10:09 am	#14
llama Octode Join Date: Jun 2006 Location: St Osyth, Nr Clacton, Essex, UK. Posts: 1,482	Re: Overheating Motek K9/RGD mono tape recorder. From the earlier posts it seems the capstan motor is linked to the capstan/flywheel by an idler wheel. I guess that's spring loaded. Can you run the thing for a while with the idler pulled away from the flywheel? That would isolate just the motor. Another thought is too much pull-in on the idler. The test above would isolate that, too. Graham __________________ Half my stuff is junk - trouble is, I don't know which half!

8th Nov 2015, 2:14 pm	#15
johnny english Retired Dormant Member Join Date: Nov 2013 Location: Liverpool, Merseyside, UK. Posts: 160	Re: Overheating Motek K9/RGD mono tape recorder. When I increased the tension on the pulley wheel spring it caused the speed to drop further so I eased off and returned it to its original setting. I then decided to strip the capstan motor down even though it was`nt squeaking or rumbling and ran freely.The top bearing was still well lubricated as was the lower one. I had previously lubricated the motor earlier as upon inspection they were quite dry. Purely by chance when looking at the lower bearing I caught a glimpse of a flat spot on the ball bearing housed at the bottom of the sintered bearing which is used as a spacer for the rotor shaft. I popped the bb out and fitted a replacement. Fitted everything back together loaded a tape and pressed play, usually within about ten minutes the speed would drop, 45 minutes later still playing at the correct speed. I ran the machine for three hours with the speed remaining stable. I can only assume that this machine was`nt regularly serviced. Regarding the high temperature of this motor (75c) I raised the deck by 10mm to aid ventilation the motor temperature has dropped to (73c).