Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

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Old November 10th 11, 02:43 PM posted to sci.electronics.repair
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Default Hoseki Digital LED Clock

Hi all

I have a Hoseki Digital LED Alarm Clock Model H-5008 / 230VAC

The primary of the tiny transformer inside has gone open.

I have some similar transformers with me but I do not know what is the
output of the original transformer. There is no marking on the pcb
about the input voltage.

Is there any way to find out? Start at a low voltage with a variac
until the unit starts working?

Any help will be appreciated.

--
Thanks in advance

ClueLess

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Old November 10th 11, 03:14 PM posted to sci.electronics.repair
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Default Hoseki Digital LED Clock

On 11/10/2011 8:43 AM, Clueless wrote:
Hi all

I have a Hoseki Digital LED Alarm Clock Model H-5008 / 230VAC

The primary of the tiny transformer inside has gone open.

I have some similar transformers with me but I do not know what is the
output of the original transformer. There is no marking on the pcb
about the input voltage.

Is there any way to find out? Start at a low voltage with a variac
until the unit starts working?

Any help will be appreciated.


Look at any filter caps near some diodes that the output of the
transformer connects to. For example, 6.3 VDC marking on the caps
means the supply probably is designed for 5 vdc.

Also look around and see if there is a small 3 pin regulator with
markings like 7805 (5 volt) or 7812 (12 volt)

Jeff


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"Everything from Crackers to Coffins"
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Old November 10th 11, 03:18 PM posted to sci.electronics.repair
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Default Hoseki Digital LED Clock

On Nov 10, 8:43*am, Clueless wrote:
Hi all

I have a Hoseki Digital LED Alarm Clock Model H-5008 / 230VAC

The primary of the tiny transformer inside has gone open.

I have some similar transformers with me but I do not know what is the
output of the original transformer. There is no marking on the pcb
about the input voltage.

Is there any way to find out? Start at a low voltage with a variac
until the unit starts working?

Any help will be appreciated.

--
Thanks in advance

ClueLess


Look at the voltage ratings on the capacitors, then go down to about
1/2 of that for the secondary voltage of the transformer. Remember,
the peak voltage is 1.414 times the nominal voltage. So, for example,
if the capacitors were rated at 50V, I would try a transformer that
gave a rectified voltage of about 35 - 40 V DC, Divide the 40V DC by
1.414 to get a transformer that had an AC output of about 25 - 30 V ac.
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Old November 11th 11, 06:40 AM posted to sci.electronics.repair
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Default Hoseki Digital LED Clock


"Clueless"


Is there any way to find out? Start at a low voltage with a variac
until the unit starts working?



** That is what I would do.

Make sure it is working just fine and then add 20 % more to cover low AC
supply.


.... Phil


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Old November 21st 11, 02:39 PM posted to sci.electronics.repair
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Default Hoseki Digital LED Clock

On Fri, 11 Nov 2011 17:40:57 +1100, "Phil Allison"
wrote:

Is there any way to find out? Start at a low voltage with a variac
until the unit starts working?



** That is what I would do.

Make sure it is working just fine and then add 20 % more to cover low AC
supply.


Thanks Phil.

I did that and found that it works at 6 volts

Thanks you and others who responded to my query.

PS: I di write to Hoseki twice but the buggers never responded. That
is customer relation, I suppose.

--
ClueLess



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