Siemens MU 1600 Repair Suggestions - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

Station X · 3rd Nov 2017, 11:28 pm

Assuming the neon lamp is fed from the mains, I'd use the recommended 100k resistor.

gizmo1990 · 4th Nov 2017, 12:56 am

Thanks Station X. Could you explain a little of the theory behind that?

Station X · 4th Nov 2017, 12:28 pm

The resistor limits the current flowing through the neon.

Looking on the internet, the recommended value appears to be 100k for a 110V supply and 220k for a 230V supply. The eBay suggestion conflicts with this as does the resistor originally fitted.

You could try a 220k first and if necessary reduce first to 150k, then to 100k.

gizmo1990 · 4th Nov 2017, 1:00 pm

Thanks again Station X. Does the higher the resistor value mean the greater resistance it offers? Or is it the opposite? I've been checking the net and nothing I've seen actually mentions this.

Station X · 4th Nov 2017, 1:02 pm

Yes. The higher the value, the more resistance, the less current for a constant voltage. Ohms Law in other words.

gizmo1990 · 5th Nov 2017, 2:14 pm

Thanks Station X, that's really useful. I'll try a 220k resistor first then.

Could I also ask what amp wire would I need that could handle this (230v) task? How do you work that out?

Graham G3ZVT · 5th Nov 2017, 11:47 pm

That's not an issue. The important thing is to make sure the bare wires cannot touch each other, or come into contact with the clock's metalwork, so either re-use the sleeving on your new neon and resistor, or salvage some replacement sleeving off some spare flex.

gizmo1990 · 6th Nov 2017, 12:43 am

Thanks for the reply @rambo1152 Isn't the max amp value of a wire important though? Seeing as though the wire needs to handle 230v? I've read that too small amp value wires can overheat and become fire risks.

Station X · 6th Nov 2017, 12:50 am

The max current carrying capacity of a wire is important, but in this case the current is miniscule, just a few milliamps.

Brigham · 8th Nov 2017, 10:20 am

It sounds like the motor's 'self start' arrangement has given up.
I've never fully understood these, so I can't help, but there are people here who can.
Is the neon intended to light the digits at night? Sounds a bit of a forlorn hope; all of those miniature neons I've seen serve as indicator lights. Just bright enough to tell you the power's on.

3rd Nov 2017, 11:28 pm	#21
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,287	Re: Siemens MU 1600 Repair Suggestions Assuming the neon lamp is fed from the mains, I'd use the recommended 100k resistor. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

4th Nov 2017, 12:56 am	#22
gizmo1990 Retired Dormant Member Join Date: Oct 2017 Location: London, UK. Posts: 12	Re: Siemens MU 1600 Repair Suggestions Thanks Station X. Could you explain a little of the theory behind that?

4th Nov 2017, 12:28 pm	#23
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,287	Re: Siemens MU 1600 Repair Suggestions The resistor limits the current flowing through the neon. Looking on the internet, the recommended value appears to be 100k for a 110V supply and 220k for a 230V supply. The eBay suggestion conflicts with this as does the resistor originally fitted. You could try a 220k first and if necessary reduce first to 150k, then to 100k. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

4th Nov 2017, 1:00 pm	#24
gizmo1990 Retired Dormant Member Join Date: Oct 2017 Location: London, UK. Posts: 12	Re: Siemens MU 1600 Repair Suggestions Thanks again Station X. Does the higher the resistor value mean the greater resistance it offers? Or is it the opposite? I've been checking the net and nothing I've seen actually mentions this.

4th Nov 2017, 1:02 pm	#25
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,287	Re: Siemens MU 1600 Repair Suggestions Yes. The higher the value, the more resistance, the less current for a constant voltage. Ohms Law in other words. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

5th Nov 2017, 2:14 pm	#26
gizmo1990 Retired Dormant Member Join Date: Oct 2017 Location: London, UK. Posts: 12	Re: Siemens MU 1600 Repair Suggestions Thanks Station X, that's really useful. I'll try a 220k resistor first then. Could I also ask what amp wire would I need that could handle this (230v) task? How do you work that out?

5th Nov 2017, 11:47 pm	#27
Graham G3ZVT Dekatron Join Date: May 2010 Location: Greater Manchester, UK. Posts: 18,711	Re: Siemens MU 1600 Repair Suggestions That's not an issue. The important thing is to make sure the bare wires cannot touch each other, or come into contact with the clock's metalwork, so either re-use the sleeving on your new neon and resistor, or salvage some replacement sleeving off some spare flex. __________________ -- Graham. G3ZVT

6th Nov 2017, 12:43 am	#28
gizmo1990 Retired Dormant Member Join Date: Oct 2017 Location: London, UK. Posts: 12	Re: Siemens MU 1600 Repair Suggestions Thanks for the reply @rambo1152 Isn't the max amp value of a wire important though? Seeing as though the wire needs to handle 230v? I've read that too small amp value wires can overheat and become fire risks.

6th Nov 2017, 12:50 am	#29
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,287	Re: Siemens MU 1600 Repair Suggestions The max current carrying capacity of a wire is important, but in this case the current is miniscule, just a few milliamps. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

8th Nov 2017, 10:20 am	#30
Brigham Octode Join Date: Mar 2006 Location: Co. Durham, UK. Posts: 1,116	Re: Siemens MU 1600 Repair Suggestions It sounds like the motor's 'self start' arrangement has given up. I've never fully understood these, so I can't help, but there are people here who can. Is the neon intended to light the digits at night? Sounds a bit of a forlorn hope; all of those miniature neons I've seen serve as indicator lights. Just bright enough to tell you the power's on.