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TAL2 powerpack


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Having got the mount set up reasonably well I've been fiddling with the powerpack and I think it's dead. There was a fuse missing which I could not get hold of anywhere. Looking at the fuse holder it would be about 3mmx15mm and rated 0.25-0.5A. I've got a new fuseholder which takes a standard 5mmx20mm fuse but there doesn't seem to be anything coming out of the transformer. Rather than spend time and money trying to sort this one out, is there an alternative readily available and reasonably priced (I'm trying to gather funds for an eyepiece).

I'd like to fix this one as it's the original, but I'm keen to check out the tracking motor.

Thanks

Jason

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Dug the transformer out in the loft.

Mine has two glass fuses.

1/ Size - 20x5mm 250mA This is mounted next to the on/off switch.

2/ Size - 20x5mm 2A This one is mounted next to the outlet plug.

Me n leccy have prior history, so I'm the last one to give advice !!

Edited by AndyH
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I can only see the one fuse holder and it definitely won't take a 5x20mm fuse.

TALtranny-1Small.jpg

TALtranny-2Small.jpg

The power is getting through to the switch but nothing from the transformer.

Is there any other transformer that will do the job?

Thanks Jason

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Hell. That's different to mine.

Mine has a simple wiring system inside. ie: wires to switch, to fuse, to transformer, to fuse, to outlet. I'll get a pic up.

I think this needs a general 'help with electronics' thread to get the attention of someone that knows about this stuff. I'm stumped. I don't know how easy it is to get hold of a 240VAC - 12VAC transformer.

Andy.

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I assume that this is aimed at producing 12v DC from a 240v ac mains supply?

The most likely culprit for failure in that case is your rectifier.

Do you have a test meter? You should see 240v ac going IN to the transformer, and around 14v ac coming out directly at the transformer, then around 12DC coming out of the rectifier heading for the fuse and the connection plug.

If you're happy to cover postage to Sunny Suffolk (if any other repair or replace options cost too much) I'd be happy to check it out for you. IF it's the rectifier I should be able to find a suitable replacement for between £5 and £10 - that's if I haven't got something lying around the place already that can be used. PM me if you need to.

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Oh, OK. thankyou.gif

There's an awful lot of "junk" in there if it's a straight step down. It's still a fair bet that it's one of the "bits" that's at fault rather than the transformer - and most of those should cost only pennies to replace - once the culprit is identified, that is.

Edited by squeaky
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Maplin list a number of 240v to 12v ac transformers. There's a 24va one at around 13 pounds, and a 48va one for around 15, or a 72va for 16. If you have a 2a fuse on the output, I'd skip the 24va one and go for one of the bigger ones - especially since it's in a sealed box. 24va = 2a at 12v, so it'd be a race to see whether the transformer or the fuse went first if overloaded. The bigger ones have more headroom and would probably run cooler since you wouldn't be running them flat out. However, they're chassis mount ones, so there is a mounting flange either side at the base so you can bolt it to something, while the photo of yours looks as though there are four bolts going through the frame. The other factor is physical size - you'd need to make sure a replacement would fit. Given that there are mains voltages in there, I'd be wary of drilling new holes through the case and using metal bolts to secure it - if you ever had a short to the frame the bolts could end up live.

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Thanks for replies and advice. When I first opened it up my first impression was that someone had added all the "stuff" in there. It seemed a bit much for a simple step down transformer.

Squeaky, I may well take you up on your kind offer. Like Andy, me and electrics don't get on too well. I already blew my 12v tester by touching 240v in there by mistake:eek:

Jerry: I'm just going to have a look through Maplins site.

Thanks again.

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Looking at that pic it looks like it could well be AC ouput...

Is the motor easy to get at and what if anything is written on it?

The two secondary windings are wired in parallel... and the output is "floating"

Edited by Psychobilly
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I don't know if this helps, but in the specs for the scope:

Voltage of supplying mains: 240/110 ± 10º

Current frequency: 50Hz (60Hz)

Output voltage of supply unit, V 12 ± 10º

(Don't know if that means the output is AC or DC. I told you electrics isn't my strong point!)

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I run my TAL using a 12V battery pack of D cells and an inverter to give 12ac. Ages ago I measured the current drawn by the motor and found it was only about 250mA, so a 24VA transformer is overspecified (assuming our scopes are similar, which is a good assumption based on our earlier discussion about this generation of TALs). Anyway, a pack of eight D cells lasts me a very long time.

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I wish I could! I guess SCS Astro (in the mid 1990's) had access to an electronics engineer or company, or sourced inverters in some other way. The scope came with a 240V mains adapter, but that's no good for mobility, so when the guy said "We'll have a battery-powered inverter available in a few months" I went for it. There are no logos or anything on the device, and on the end of the output lead is the right-shaped socket to plug into the scope. And just in case you forget, there is a hand-written label next to the plug that reads "Motor 12V AC 50Hz". This was obviously made up specially for the TAL scope.

post-30909-133877783276_thumb.jpg

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Hi all,

Richard, I am very interested in getting a battery pack for the 2M, too... Please include me if you send an update on this!

Back to the OP for a sec, I have just had a look in my transformer and it is pretty much identical to Andy's, except the wires that are white in Andy's are blue in mine. The fuse on mine is marked T2A L250V (presumably 2A @ 250V).

It is hard to tell from jason.p's pic but there COULD be a rectifying circuit in there. As Andy says, the original DEFINITELY has 12V AC output (the speed of the motor is governed by the output frequency) so - could somebody have been messing with jason.p's and put a DC motor in the mount? I think it is pretty important to ascertain this before making changes to the transformer.

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