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Old 6th Dec 2017, 7:28 pm   #1
aechopan
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Default Alba 3112: completely disoriented

Dear all,

I am part of this since this very day. Previously I have enjoyed reading many of you about details I wish somebody told me before.

I got an ALBA 3112, and I have decided to refurbish it, despite my lack of experience. I know that the radio has been plugged into 230V, so my guess it is that some component is burnt. The problem is that I am completely disoriented, and I was hoping that any of you could guide me through the first steps of my new and confusing adventure

Some of the capacitors are leaking wax, clearly they will need to be replaced. But still I would not know which part of the device is toasted by being being connected in the 230V net before changing the voltage selection link.

Thanks a lot!!

Last edited by Station X; 6th Dec 2017 at 10:06 pm. Reason: Forum Rule Compliance.
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Old 6th Dec 2017, 10:19 pm   #2
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Default Re: Alba 3112: completely disoriented

Hello and welcome to the forums.

As I understand it this set was connected to the mains with the voltage selector set incorrectly?

Snip out C31 the mains filter cap which may go bang if it hasn't done so already.

WITH THE SET TURNED OFF

Using a meter check the value of R21, R22 and R24.

Check the valve heaters for continuity.

Report back the results and someone will advise you.
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Old 7th Dec 2017, 12:05 pm   #3
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Default Re: Alba 3112: completely disoriented

Hi Alex

I just taking a guess at your first name, forgive me if I have got it wrong, however, a big welcome to our lovely forum, here you will find lots of help from a vast amount of members who are retired radio and TV service engineers, technicians and other forms of engineers all will give advise and help so no need to be afraid of asking even the most silly question. And provided you have the circuit diagram and service info for this set you will be able to follow Grahams advice, but as you work through the set hi light the components as and when or if you replace or check them that way you will not forget where you got to. There are plenty of books with radio, tv and electronic information around and you can even pick up a bargain on this forum.

Good luck

Best wishes

Ken
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Old 7th Dec 2017, 12:36 pm   #4
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Default Re: Alba 3112: completely disoriented

The "Trader" service sheet is available from the Vintage Service Data at the top right of this page for 1.99, a bargain.
It will assist you greatly.
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Old 10th Dec 2017, 9:47 am   #5
aechopan
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Red face Re: Alba 3112: completely disoriented

Sorry for the late reply, some screws were impossible to dismantle with a screwdriver!

Following your instructions I have:

- snipped out C31, I got a replacement (0.022 uF instead 0.02)
- looking for a replacement for C28, the tone corrector, looks very bad and greasy
- R21 reported 255 Ohm
- R22 reported 952 Ohm
- no resistance could be measured in R24, seems faulty

I could not check the valve heaters continuity, because I am not sure how it is done

Thanks for the advice! I got the service sheet, but it is still a bit tough for me anyway
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Old 10th Dec 2017, 1:33 pm   #6
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Default Re: Alba 3112: completely disoriented

Quote:
Originally Posted by aechopan View Post
I could not check the valve heaters continuity, because I am not sure how it is done
Just treat them as resistors and measure between the relevant base pins (with the set disconnected from the mains, of course- unless you have a really good meter, they don't like trying to measure the resistance of the national grid!).

A check from chassis to point C in the circuit snippet in post #2 will check the whole chain in one go, including the dropper resistor, if that's not OK, you'll need to prod individual sections/valve heaters.
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Old 10th Dec 2017, 6:39 pm   #7
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Cool Re: Alba 3112: completely disoriented

Thanks Herald!

I did, and valves seem to show continuity connecting to point C. Thanks for the advice.

So, in summary:

- snipped out C31, I got a replacement (0.022 uF instead 0.02)
- looking for a replacement for C28, the tone corrector, looks very bad and greasy
- R21 reported 255 Ohm
- R22 reported 952 Ohm
- no resistance could be measured in R24, seems faulty
- valves continuity seems OK

My best shot would be to replace C31, C28 and R24 so far...?
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Old 10th Dec 2017, 7:28 pm   #8
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Default Re: Alba 3112: completely disoriented

The set should work without C31. If you're going to replace it you must use a Class X capacitor in this position.

R24 is a shunt for the scale lamps, so these may have failed too.
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Old 11th Dec 2017, 1:47 am   #9
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Default Re: Alba 3112: completely disoriented

When you say "no resistance could be measured in R24, seems faulty" do you mean that it had a resistance of 0.0 ohms, or that no continuity could be measured (much more than the expected few ohms or tens of ohms), such as over 1 megohm?
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Old 11th Dec 2017, 10:16 am   #10
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Default Re: Alba 3112: completely disoriented

A simple test would be to connect your meter on ohms range to the live and neutral pins of the mains plug. With the set turned on you should read around 1200 ohms. If you see infinite resistance, short-circuit R24 and see if the reading is then correct.
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Old 11th Dec 2017, 10:51 am   #11
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Default Re: Alba 3112: completely disoriented

With the set turned on but not plugged in !!
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Old 11th Dec 2017, 10:56 am   #12
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Default Re: Alba 3112: completely disoriented

It would be a bit difficult to connect to the pins with the set plugged in!
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Old 11th Dec 2017, 1:05 pm   #13
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Default Re: Alba 3112: completely disoriented

Take the top off the plug?

Don't try this at home, as they say!
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Old 11th Dec 2017, 1:12 pm   #14
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Default Re: Alba 3112: completely disoriented

OK, but I'm not going to prefix every post I type with pages of safety warnings. I expect people to exercise "common sense", even though there is no such concept in law.
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Old 11th Dec 2017, 1:52 pm   #15
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Default Re: Alba 3112: completely disoriented

Agreed, it can go over the top.
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Old 16th Dec 2017, 2:45 pm   #16
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Smile Re: Alba 3112: completely disoriented

Quote:
Originally Posted by Station X View Post
A simple test would be to connect your meter on ohms range to the live and neutral pins of the mains plug. With the set turned on you should read around 1200 ohms. If you see infinite resistance, short-circuit R24 and see if the reading is then correct.
You all are great, guys, thanks a lot for all the advice and patience.
Sorry also for the late reply, I am a doctoral student and I had a deadline this week.

I just checked the value of the resistance measured between the + and - mains when switched on. The multimeter registered 0, so I shortcircuited R24 it as you suggested, StationX. The value reported is ca. 1329 Ohm.

My guess for next steps would be:

-Replace that resistor (R24) for a modern one (100 Ohm, 0.25 W).
-Replace capacitors evidently leaking:
  • C31 with 0.022Uf Class X1, 440V
  • C28 with 4.7nF Mylar/Polyester, 100V
-Replace the scary mains cable made of nylon by a modern one (2-Core 3A).

Does anything sound crazy?
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Old 16th Dec 2017, 4:12 pm   #17
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Default Re: Alba 3112: completely disoriented

That does not sound like a crazy strategy.

I would also replace C26 the audio coupling capacitor. A faulty cap here could do lots of damage.

Just one point:-

Quote:
The multimeter registered 0
That would indicate a short-circuit, which you clearly don't have. It's more likely that the meter showed infinity (analogue meter) or 0L (Digital Meter).

Statements like "no reading", "no resistance" and "zero reading" have often lead us up the garden path.

If in doubt, check what the meter shows on ohms range with no leads connected. Whatever it is, denotes infinite resistance.
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Old 16th Dec 2017, 4:24 pm   #18
aechopan
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Post Re: Alba 3112: completely disoriented

It is undoubtly 0L, thanks for the terminology clarification, very much needed!
I will keep you posted with my progress!
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Old 16th Dec 2017, 4:34 pm   #19
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Default Re: Alba 3112: completely disoriented

One other point. I'd be inclined to use a 2 Watt resistor for R24. With no scale lamps fitted it will be carrying 100mA equating to 1 Watt.
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Old 16th Dec 2017, 4:43 pm   #20
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Default Re: Alba 3112: completely disoriented

Quote:
Originally Posted by aechopan View Post
My guess for next steps would be:

-Replace that resistor for a modern one (100 Ohm, 0.25 W).
-Replace capacitors evidently leaking:
  • C31 with 0.022Uf Class X1, 440V
  • C28 with 4.7nF Mylar/Polyester, 100V
-Replace the scary mains cable made of nylon by a modern one (2-Core 3A).

Does anything sound crazy?
If you mean R24 the 0.25 watt rating won't be enough, power dissipated will be Isquared*R, which in the event of a bulb failure will be a lot higher, at least 2.5 watts or possibly more because the resistor in a failed bulb situation will be passing the heater current and the HT rectifier current, for cooler running use a 5 watt job.

C31...X2 class will be ok if you can get one.

You need to up your voltage rating for C28, 630 VDC should be ok.

Lawrence.
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