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Old 14th Jan 2018, 3:30 am   #1
jamezx88
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Default Hitachi SR-302 light bulb identification

Hi all,

Need help in identifying a light bulb!

Bought a Hitachi SR-302 recently which was turning on but not working, but very clean given the age. After opening up found the fuses were blown, and after replacing them the system is 95% running (and sounding pretty good). The only thing that doesn't seem to be working are the back lights.

Curious if anyone could assist in identifying the bulb in the attached photo. I've snipped it out of place but there about 5 in the unit (all of which are burnt out).

Also, had it running now for about 30 mins and there is a bit of heat coming from it. Guessing that is normal?

Cheers,

James
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Old 14th Jan 2018, 4:01 am   #2
Refugee
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Default Re: Hitachi SR-302 light bulb identification

Are you sure the voltage selector is set correctly? It looks like those bulbs have been running very hot.

I have to watch our voltage in sunny weather as an awful lot of solar panels have gone up in our area and some of them have literally melted their cables leaving a carbon footprint on a power pole.

On a sunny day with regular passing clouds the voltage can go up and down quite a bit.
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Last edited by Refugee; 14th Jan 2018 at 4:06 am. Reason: Left an "a" out
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Old 14th Jan 2018, 4:10 am   #3
jamezx88
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Default Re: Hitachi SR-302 light bulb identification

Hmm, I'm not sure, but I'm guessing it would be default 240V?

After about an hour it started to get even hotter (specifically the metal plate in the centre) so I switched it off.
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Old 14th Jan 2018, 4:29 am   #4
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Default Re: Hitachi SR-302 light bulb identification

All you need to do is to check the voltage plate on the back and set the voltage selector to 240/250V.
If it is 220V only there is a work around but it is a bit cumbersome.
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Old 14th Jan 2018, 4:36 am   #5
jamezx88
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Default Re: Hitachi SR-302 light bulb identification

No 'voltage plate' selector that I can see?
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Old 14th Jan 2018, 8:55 am   #6
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Default Re: Hitachi SR-302 light bulb identification

Quote:
Originally Posted by jamezx88 View Post
Hmm, I'm not sure, but I'm guessing it would be default 240V?

After about an hour it started to get even hotter (specifically the metal plate in the centre) so I switched it off.
The metal plate is a heatsink, intended to dissipate heat produced (mostly) by the output transistors. It's therefore normal for it to get hot, particularly if the set is used at high volume. If it's getting very hot at idle, though, it might be worth checking the bias on the output devices.
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Old 14th Jan 2018, 9:55 am   #7
vidjoman
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Default Re: Hitachi SR-302 light bulb identification

Check your speaker wiring - the pair shown in the photo are wrongly connected.
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Old 14th Jan 2018, 11:09 am   #8
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Default Re: Hitachi SR-302 light bulb identification

Two speakers should always be connected, one to the (+) & (-) terminals of the Left Channel, and another to the (+) & (-) terminals of the Right Channel. If, as it appears from the photo, two rows of speaker terminals are fitted, there should be a front panel switch, usually marked something like speakers (A) & speakers (B). Connect one speaker to each of the (A) outputs, and ensure that the speaker selector is set to (A). You have One speaker connected to the (-) terminals of both the (A) & (B) outputs of one channel. I'm amazed you could hear anything with that connection, and, if left that way serious damage will result i.e. failure of the output devices.
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Old 14th Jan 2018, 11:30 am   #9
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Default Re: Hitachi SR-302 light bulb identification

I think the speakers may be wired with coaxial cable, which is why it looks wrong. I think the screens are connected to the (-) terminals and the centre conductors to the (+). This is not the right sort of cable for speakers.

As for the bulbs, personally I would substitute LEDs for them, but that would need a bit of experimentation, depending on the voltage being fed to them.
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Old 14th Jan 2018, 11:41 am   #10
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Default Re: Hitachi SR-302 light bulb identification

According to the schematic, each bulb on that panel is 6.3 volt at 250mA.

Lawrence.
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Old 14th Jan 2018, 1:07 pm   #11
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Default Re: Hitachi SR-302 light bulb identification

If coax has been used, then, although incorrect, the stereo should still work, but it appears to me that one speaker is connected to the 'A' output of one channel, whilst the other is connected to the 'B' output of the same channel. Unless my old eyes deceive me, the upper row of terminals are the 'A' outputs, and the lower row those for the 'B' outputs. One speaker should be connected to one of the RH channel outputs, and the other to the LH channel output on the same horizontal row. (Apologies if I'm misreading the labelling of the terminal strip)
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Old 14th Jan 2018, 1:14 pm   #12
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Default Re: Hitachi SR-302 light bulb identification

Apart from the use of coax the wiring looks correct to me. The 'A' outputs are on the right of the panel and the 'B' outputs are on the left of the panel.
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Old 14th Jan 2018, 1:30 pm   #13
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Default Re: Hitachi SR-302 light bulb identification

The voltage plate in post#5 does show 240V.
Our voltage commonly creeps up as far as 255 volts on a regular basis. You could have the same problem.

Reducing the power to the bulbs or fitting LEDs will sort out the lighting.
Turning down the bias pot inside after reading the service manual should work for the heat problem if done while the mains voltage is a little on the high side.
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Old 14th Jan 2018, 1:50 pm   #14
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Default Re: Hitachi SR-302 light bulb identification

Anyone figured out the loudspeaker switch position connections for A+B yet on the schematic.

Lawrence.
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Old 14th Jan 2018, 3:56 pm   #15
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Default Re: Hitachi SR-302 light bulb identification

Quote:
Originally Posted by jamezx88 View Post
Need help in identifying a light bulb!
They're axial wire ended bulbs. Once common, they've more or less disappeared now.
I found these: https://www.ebay.co.uk/itm/Pack-of-1...MAAOSwg8tZ7i1B, but the postage won't be free to Australia!
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Old 14th Jan 2018, 5:36 pm   #16
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Default Re: Hitachi SR-302 light bulb identification

As I noted is a thread relating to a Sharp Stereo, CPC stock 12V/60mA Festoon (i.e. axial wire-ended) bulbs -part no. SC12498 @ 79p each. These may also be suitable for the Hitachi SR-302.
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Old 14th Jan 2018, 5:44 pm   #17
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Default Re: Hitachi SR-302 light bulb identification

See Post# 10.

Lawrence.
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Old 14th Jan 2018, 8:32 pm   #18
dseymo1
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Default Re: Hitachi SR-302 light bulb identification

Search '6v 1.5w festoon' on eBay - 10 for 3.99. Just solder on your own wires.
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Old 15th Jan 2018, 6:51 am   #19
jamezx88
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Default Re: Hitachi SR-302 light bulb identification

You are absolutely right re: speaker wiring causing the overheating. Disconnected one part and it stayed cool for a few hours. Will re-connect using the instructions above.

Re: light bulb. Would these do?

https://www.ebay.com.au/itm/6v-Festo...0AAOSwt5hYicnM

Or these?

https://www.ebay.com.au/itm/6v-Festo....c100005.m1851

Would also be happy to change to LED strip if not too complicated? I think I have one lying around somewhere

Cheers

James

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Old 15th Jan 2018, 12:39 pm   #20
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Default Re: Hitachi SR-302 light bulb identification

That's a neat looking amp- I'm something of a fan of these '70s/'80s receivers, generally well-built and long-lived, though they latterly got derided as behemoths. Is there a possibility that a strand of outer braid has bitten through the inner insulation on one side, overloading one amp channel without necessarily muting it?- some coaxial cables have quite soft inner insulation and twisting up the outer braid into a pigtail can cut into it. A more exotic possibility is that the amp might be going unstable with an unusual cable like this- most amps were designed to cope with a wide range of loading permutations but there's a limit to how much extraneous capacitance/inductance some could cope with. This was an Achilles' heel of some fancy audiophile amps that cut back on compensating components for purist motives- unlikely with a mass-market amp like this, but an outside possibility if the basic checks don't show up something like a partial short.
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