Author Topic: HP 3325A , Need Repair help  (Read 681 times)

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Offline GigaJoeTopic starter

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HP 3325A , Need Repair help
« on: November 13, 2023, 07:01:19 pm »
HP 3325A:

errors on self test  2, 3 (seems misleading )

Output on display: 29mV P-P: 
NOTE:  Output not terminated to 50 Ohm
scope CH1  AC , and DC are present from  generator output  at lower peak of waves  ( like DC offset , but it OFF)


output on display:  30mV P-P:
same DC offset "0" at bottom of sineway



Then I shorted ACD ,
all tests pass ,   1V P-P , became 2.1V P-P  unterminated ,  and everything works , but
no DC offset regulation

this test pass with +20mV off:



and im lost  a bit ,  looking for direction ....

Found -   LM311 , A14 board
Fixed , now it need adjustment ...  calibration , at the level i can do ....
« Last Edit: November 13, 2023, 09:10:18 pm by GigaJoe »
 

Offline m k

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Re: HP 3325A , Need Repair help
« Reply #1 on: November 14, 2023, 09:35:29 am »
Since triangle is based on square and square is based on sine one can expect the problem is quite far back.

Since disabling Auto Cal removes the problem one can think that Auto Cal is the problem.
Top is still round, so offset is available.

Should peak detector find it during self test 1?
Maybe it's just a timing thing.
Advance-Aneng-Appa-AVO-Beckman-Danbridge-Data Tech-Fluke-General Radio-H. W. Sullivan-Heathkit-HP-Kaise-Kyoritsu-Leeds & Northrup-Mastech-OR-X-REO-Simpson-Sinclair-Tektronix-Tokyo Rikosha-Topward-Triplett-Tritron-YFE
(plus lesser brands from the work shop of the world)
 

Offline m k

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Re: HP 3325A , Need Repair help
« Reply #2 on: November 17, 2023, 10:33:59 am »
DAC to DC offset is controlled by HMD5 thru A14U29 as K5 to S/H latch A14U26 and strobed thru data decoder A14U27.
K5 is also setting Preset Up/Down Counters A14U6 and U8.
HMD5 is receiving level data thru A14U30.
Div 3 relay pad out is controlled by K5 thru A14U30, so is ramp reset thru A14U1.
Clearly K5 itself it most likely is not.

Function selector A14U28 uses K0-4.
After that actual "discrete" selector components are still many.

DC Offset Control has only function enablers and Offset Error.
Nothing that is directly ACD related.

ACD is outputted to HMD3 with level data.
So it is a digital info thing only and then is not controlling anything directly.
Advance-Aneng-Appa-AVO-Beckman-Danbridge-Data Tech-Fluke-General Radio-H. W. Sullivan-Heathkit-HP-Kaise-Kyoritsu-Leeds & Northrup-Mastech-OR-X-REO-Simpson-Sinclair-Tektronix-Tokyo Rikosha-Topward-Triplett-Tritron-YFE
(plus lesser brands from the work shop of the world)
 


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