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Test Equipment [Closed] EPROM Eraser UV141; Fault

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crustytv
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As I sit here typing this, I have the mother of all sore throats, never have I experienced such pain, and I openly admit, it has resulted in a little boo. My tonsils are so large they are dangling on the back of my tongue, resulting in me constantly trying to swallow them. I've not slept properly for two days, nor have I eaten, equally difficult to drink and swallow. Can I get to see a doctor? No earliest appointment is 30th Aug. Apparently I can try each day from 8am and take pot luck with every other poor sod who needs to be seen. This flaming country is broken!

Anyway, what you might ask has that got to do with the device on the bench? Not much other than I'm trying desperately to take my mind off all this and occupy myself. Truth be told, it's not helping that much, and I'm hardly at my best problem-solving. Still, the alternative is to sit around and do nothing which is not good either, hence seeking sage advice here.

This device powers on, but that's about it, the UV light does not come on, yes the tube is fine, both filaments at each end are intact. I also tested the tray micro switch that the tray engages, and acts as an interlock. The microswitch has no continuity when open and does have continuity when closed.

I have mains 240V into the PCB, and I would expect 240V on the starter transformer wires, but I only have 9V! Without a cct I'm unsure as to what the cause might be. I'm wondering what that rectangular box is. The reason I'm fixated on that, is it straddles the live 240V and the upper output to the starter TX, is this some sort of fuse?

 I know it's a long shot but any idea lads?

20230817 155614
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20230817 144159
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20230817 144541
20230817 144627
20230817 144638
20230817 144645
20230817 154146

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Posted : 17/08/2023 2:29 pm
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Nuvistor
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@crustytv 

Sorry Chris, never seen one so I am of little help.

OK on the sore throat, hope it eases off in the next 24 hours, getting an appointment at some doctors is pot luck. Not sure what mine is like at the moment but they do like telephone appointments.

Anyway take care and be careful near the 230volt wires while not feeling the best.

Frank

 
Posted : 17/08/2023 3:22 pm
Lloyd
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Sorry to hear about your throat troubles, Chris, hope you feel better soon! All I can say about the doctors is good luck… ours have some sort of online booking system, which I haven’t bothered trying to use yet.

That little white box, I notice it says ‘Omron’ on it, I normally associate them with relays, so I wonder if that’s what it is? I’ll try googling the number on it and see what comes back. If it has 5 or 6 legs then I think it could be one.

Regards,

 Lloyd 

 

Edit:

yes, it’s a relay, Omron LCIN-10 brings up an eBay listing with a PCB with 2 sat on it that look similar. My guess is the timer on the front energises the relay to turn on the UV tube for however long it’s set for, so when you set the timer going it should click on, so there should be about 9-12V going into 2 pins opposite the ones that have the live connections. 

 
Posted : 17/08/2023 4:13 pm
slidertogrid
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Get well soon Chris. Same here getting a Doctor. Casualty is usually full of drunks and druggies so the wait is massive. As you say broken Britain.   

 
Posted : 17/08/2023 4:43 pm
crustytv
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Posted by: @lloyd

it’s a relay, Omron LCIN-10 [..] My guess is the timer on the front energises the relay to turn on the UV tube for however long it’s set for, so when you set the timer going it should click on, so there should be about 9-12V going into 2 pins opposite the ones that have the live connections. 

Ah, I see, thanks Lloyd. 👍 

One thing for certain, when the erase switch is pressed, there isn't a click from the relay. Guess I will need to remove it from the PCB to perform some tests.

edit:

I wonder, could I temporarily by-pass the relay with a jump wire so that the cct is always on? That way I could prove or disprove the relay.

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Posted : 17/08/2023 7:07 pm
Jayceebee
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Sorry to hear you're unwell Chris and hope you are back on form soon. Same situation with doctors here also but have you tried ringing 111 for advice?

On the fault does the erase light come when you press the button? Measure the voltage on the anode and cathode of the diode next the relay straight after powering on then after the button is pressed, I would expect the voltage on the anode to fall the instant the button is pressed. You could also measure the resistance of the diode, I would imagine it would be a few tens of ohms to a couple of hundred. If it measures as a diode then the relay coil might be o/c.

John.

 
Posted : 17/08/2023 7:16 pm
crustytv
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Posted by: @jayceebee

On the fault does the erase light come when you press the button?

It does not

Power ON test of diode

Anode = 22.9V
Cathode =22.8V

Power On test with erase button depressed

Anode = 22.4V
Cathode = 22V

Resistance across diode

101R

Continuity test

shows full continuity across diode, but is this due to the relay coil being in circuit?

Diode Test

0.0766V

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Posted : 17/08/2023 7:28 pm
Jayceebee
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So it looks like the coil is not being energised by the timer and yes with the continuity test you are reading the coil resistance. There is a small transistor below the diode, try the same tests monitoring it's voltages. I'm suspecting the collector will be connected to the coil and diode, the base will interface with the 40xx ICs and the emitter will be ground. The base should go to 0.6-0.7v when the timer button is pressed and should stay there. You could also see what is on pin 16 of the 40xx and pin 8 of the 4 pin IC which I suspect is an NE555.

John.

 
Posted : 17/08/2023 8:03 pm
crustytv
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@jayceebee

The transistor is a BC182L

Power ON Test

B=23.2V
C=23.3V
E=23.2V

Power On test with erase button depressed

B=23.1V
C=23.1V
E=23.1V

555 Timer IC power on test

Pin 8= 23.2V

555 Timer IC power on test with erase button depressed

pin 8 =23V

There are two other IC's but are both 14-pin

MC14024BCP pin 14 23.3V / 23.2V with erase button depressed
MC14025BCP pin 14 23.3V / 23.2V with erase button depressed


MC14024BCP - Counter/Divider Single 7-Bit Binary UP 14-Pin PDIP
MC14025BCP - Quad 2-Input NOR GATE , Package: Pdip, Pins=14

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Posted : 17/08/2023 8:23 pm
Jayceebee
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Posted by: @crustytv

@jayceebee

The transistor is a BC182L

Ok, i could tell by the print that it didn't look like a normal BC107 pinout with the base in the middle. Where do you have the -ve probe of your meter? With 23V everywhere either you are not on the correct ground point or there is an o/c somewhere. Ground should be pin 7 of the 14pin ICs and the -ve connection of the 1000uF cap and possibly the emitter of the transistor. The volts between pins 7 & 14 is a maximum of 15V.

 

John.

 
Posted : 17/08/2023 9:02 pm
crustytv
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I was on the chassis for -ve, apologies for that, I'll redo all measurements

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Posted : 17/08/2023 9:09 pm
crustytv
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Repeat tests, GND on pin 7 of 14-pin IC

Power ON Test

B=1.5mV
C=5.2mV
E=373mV

Power On test with erase button depressed

B=1.5mV
C=2.2mV
E=373mV

555 Timer IC power on test

Pin 8= 5.2mV

555 Timer IC power on test with erase button depressed

pin 8 =2mV

There are two other IC's but are both 14-pin

MC14024BCP pin 14 5.2mV/ 5.2mV with erase button depressed
MC14025BCP pin 14 5.2mV / 5.2mV with erase button depressed

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Posted : 17/08/2023 9:17 pm
crustytv
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Edited the above

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Posted : 17/08/2023 9:22 pm
Jayceebee
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Ok with only 5mV or so on on the IC's looks like the supply is missing possibly a o/c mains transformer primary or 5V regulator if there is one.

Edit. can't see any sort of regulated supply so check the volts across the 1000uf. If it's only mV and the cap is not short then my money is on the transformer. 

John.

 
Posted : 17/08/2023 9:26 pm
crustytv
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No regulator, just a TX 😥 

20230817 222844
20230817 222900

Yet again I'm a magnet for the broken stuff, I wouldn't mind, but it was £100. I didn't like the look or safety of the cheap Chinese ones, so thought this was better. Err No!

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Posted : 17/08/2023 9:31 pm
Cathovisor
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The good thing is that - I think - is an off-the-shelf component, but a bit wimpy IMO. Hopefully you can get a 6VA transformer with the same pin spacings, something like this perhaps?

https://cpc.farnell.com/vigortronix/vtx-120-4206-406/transformer-6va-2-x-6v/dp/TF01311

 
Posted : 17/08/2023 9:36 pm
Jayceebee
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How much? £100, seriously! Can you return it?

 

What is the resistance across the primary pins 1,2,3,4?

John.

 
Posted : 17/08/2023 9:38 pm
crustytv
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The Chinese ones are over £50, and they are in flimsy plastic cases, with 2-pin plug. Also when the UV lamp is on, you can see it radiating through the case 😲 

So that's why this looked a good option. They were £76 brand-new back in the day. I looked at other period ones, and they were even more expensive. There's another of these over 180 euro.

Posted by: @jayceebee

What is the resistance across the primary pins 1,2,3,4?

O/L across the lot and no returns accepted on the device.

@cathovisor you're a star Mike, I cannot than you enough, one ordered.

@jayceebee, thanks to you also for walking me through the diagnosis 👍 

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Posted : 17/08/2023 9:55 pm
Jayceebee
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If you have a spare wall wart between 9 & 12V wire it across the 1000uf (observing the polarity of course) and it should work.

John.

 
Posted : 17/08/2023 10:07 pm
crustytv
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Removed, awaiting new TX, poor thing looks dishevelled.

20230817 230634

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Posted : 17/08/2023 10:08 pm
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