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Old 9th Feb 2019, 6:16 pm   #5
factory
Hexode
 
Join Date: Jul 2009
Location: Cheshire, UK.
Posts: 337
Default Re: HP T141 Display section repair

HP seemed to change to using the 1% tolerance resistors sometime in the 1960's, which is why you find a lot of odd values used, even when an earlier build of the same instrument may use standard 5% or 10% types instead.

Were the failed resistors the metal film ones? I found they can fail high in value or open circuit, sometimes without showing any visible signs of distress.
The metal film resistors HP used in the 1960's & 1970's do seem to be slightly less reliable then the carbon composition ones, despite the latter having a worse reputation in vintage stuff.

I bought myself a 141S SA last year, the power supply for that uses the same main PCB as the older 140A/B scopes & non storage 140T display section, the 141T looks very crammed by comparison.
The plastic covers for the adjustment pots in my 141S seemed to have reacted badly to something, it's the first time I've seen any crazed, cracked of missing, I don't know if this is a common problem or a minor problem with small batch of them due to the type of plastic used.

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David

P.S. shouldn't the title refer to the 141T not the T141?
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