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Products => Test Equipment => Topic started by: SAUL BRITTO on May 14, 2014, 02:27:51 am

Title: Vertical position problem scope HP1740A
Post by: SAUL BRITTO on May 14, 2014, 02:27:51 am

 I bought  an old scope HP 1740A but with a vertical position problem,and thought it was the big hibryd vertical out,wasn't the chip but two resistors named R1,R5, that receives the signal from delay line 100ns,they are 1.2k,on DMM measure was 1.9k.

Same problem i found in other forum: http://www.electro-tech-online.com/attachments/aaesp07-gif.44411/ (http://www.electro-tech-online.com/attachments/aaesp07-gif.44411/)

This looks like a classical failure in these oscilloscopes.

Title: Re: Vertical position problem scope HP1740A
Post by: tautech on May 14, 2014, 03:04:41 am

Thanks for posting your thread here.  :-+

Title: Re: Vertical position problem scope HP1740A
Post by: SAUL BRITTO on May 14, 2014, 03:09:26 am

Quote from: tautech on May 14, 2014, 03:04:41 am

Thanks for posting your thread here.  :-+

is always a pleasure to help friends!  :-+

Title: Re: Vertical position problem scope HP1740A
Post by: lowimpedance on May 14, 2014, 03:17:58 am

I have also had found R3 can drift high and basically shift the DC bias through out the preceding hybrid making it appear dead, ie signal at input but nothing on the CRT. Having played a bit with these vintage HP CRO's I have found the Hybrids to be reliable and less likely to be the cause of trouble compared to the more generic parts around them etc.

Edit: I mentioned this quite some time ago in the restoration of a 1741 thread by Tekfan.
Quite a deal of info there if you wish to search

Title: Re: Vertical position problem scope HP1740A
Post by: ddelectrical on May 21, 2017, 08:59:33 pm

Just repaired a hp1740a with no trace. A5Q1 open circuit. Replaced A5Q1 and A5Q3 as a pair and alls well. No bad resistors in  this one. Used 2N3906 pnp.