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Old 11th Jul 2017, 1:06 pm   #1
ben
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Default Thorn TX100B - relay chatter

Just turned on an old Fergy 51A2 /Tx100b I have in storage, no audio or raster but a machine gun- style relay chatter. Presumably a short in the line stage.

I have no test equipment here so I took a look at an online list of stock faults

I have changed the 47uF/160v HT cap and a couple of others (c117 100uF, c119 22uF) in the PSU, all of which looked to have had a hard/hot life (though not bulging or leaking). Plus I swapped the T6071V for a BU508A I had around, along with the insulation sheet - no change. The list suggests D28 BY299 as possible cause but I'll be damned if I can find it! Any ideas?

The line output transformer has a yellow spot/sticker on, is this a good sign?

I will hopefully get hold of a multimeter here over the next few days so as to be able to do some proper fault finding.
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Old 11th Jul 2017, 1:24 pm   #2
Records
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Default Re: Thorn TX100B - relay chatter

Was there a version of this made by Bush ?
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Old 11th Jul 2017, 1:47 pm   #3
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Default Re: Thorn TX100B - relay chatter

Hi Ben, a chattering relay was indeed a sign of distress in the line output stage. Try disconnecting the base of the BU508A, if it still chatters then it possibly is but not aiways a faulty LOPT. Up until the TX100 LOPTs used in Thorn chassis were super reliable, I believe these were made by Hitachi the most unreliable one being that used in the 110 degree FST (no spot), followed by 22"/26" 30AX (green spot), 20" 90 degree (blue spot) and the most reliable, 21" 90 degree FST (yellow spot).

You wont find D28 fitted to your set, it was in 110 degree models only.


Quote:
Originally Posted by Records View Post
Was there a version of this made by Bush ?
No Bush was ever fitted with a Thorn chassis but there was a Bush badged Vestel set that looked very similar to the Ferguson 51G3 range.

John.

Last edited by jayceebee; 11th Jul 2017 at 2:15 pm. Reason: More info
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Old 13th Jul 2017, 12:03 pm   #4
Welsh Anorak
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Default Re: Thorn TX100B - relay chatter

Usually in this model the BU will have failed due to a dry joint in the line drive stage. Like John says, the yellow spot LOPTs were pretty reliable. I know I have a new LOPT for a TX100 (not the usual green spot one) so if you need one I'll check and see which it is.
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Old 22nd Jul 2017, 1:12 am   #5
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Default Re: Thorn TX100B - relay chatter

Thanks John and Glyn for the responses.
The line o/p transistor tested s/c ( B-E). I am assuming the replacement met a similar fate. No obvious drys on the stage but will take a closer look. Had to put it to one side for now but will update once I've investigated more.
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