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6674A replacement LCD does not display - a contrast adjustment issue?

Question asked by drkirkby on May 14, 2016
Latest reply on May 16, 2016 by drkirkby

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I have an HP 6674A option J06 (70 V, 30 A) PSU - the S/N is 3501A-00797. This was shipped and somewhere between leaving the US and reaching the UK, the display cracked, although some bits of characters could be seen.

I contacted Keysight in the UK to ask what is the replacement part would cost. I was told I needed 5065-7075, which I ordered and fitted. Unfortunately the display does not show anything at all, whereas the damaged one does at least show some characters. Below are the two displays - the original (P/N 5181-2813) one fitted and the replacement Keysight sent (5065-7075).

Are these two displays compatible in the 6674A?

Someone suggested it is probably necessary to adjust the contrast, but a search of both the user and service manuals does not tell me where the pot is for that. Can anyone tell me where I will find the adjustment pot?

PeterW May 16, 2016 10:20 AM

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Hello Drkirkby,

The 6674A you are attempting to repair was manufactured prior to 1995. Many changes have occurred to both the hardware and firmware in that particular instrument. The GPIB interface and even possibly, the front panel itself will require replacement to enable the new display to function correctly with an instrument of that age.

I suggest that the unit be returned to Keysight for repair.

Regards

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PeterW May 16, 2016 10:20 AM

Hello Drkirkby,

I suggest that the unit be returned to Keysight for repair.

Regards

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drkirkby May 16, 2016 2:37 PM

Thank you PeteW.

Keysight made me aware of service note 6674A-10, which says the keypad needs replacing with 5040-1735 plus a cable 5080-2261. There's no mention of the GPIB interface in that, but perhaps you know that on a unit of this age, the GPIB needs replacing too. It is clear there's a cable directly linking the GPIB to the keypad.

I have got this working now, by

1) I removed a display (5063-2305) from a 6643A (35 V, 6 A, 210W) . The 5063-2305 worked in the 2100 W 6674A. Unfortunately the display indicated "Serial down". I believe that there was a fault on the 5060-3399 GPIB board, and this is nothing to do with swapping the displays, as the bad display shows some characters, and whilst I could not read them completely, what I can see is consistent with "Serial down".

2) Removed the GPIB board (5060-3399) from the 6674A and put in the same part number (5060-3399) I took from the 6643A.

At that point, the 6674A is functioning. Obviously the 6643A no longer functions, but the 6674A is a much more useful power supply to me, as it is twice the voltage (70 vs 35 V), and 5 times the current (30 A vs 6 A) of the 6643A.

Several large electrolytic capacitors are showing signs of bulging in the 6674A, which is quite common in old capacitors as I am sure you know. So I would not be surprised if the 6674A is not meeting its specifications for noise, but it is at least functioning.

I will order up some capacitors. Some are 6000 uF @ 100 V. The others I will have to remove to see their values. It will take a bit more work, but I think I will get this thing working properly.

BTW, I noticed that there are at least two version of the GPIB board 5060-3399. The one I took from the 6643A looks the same as the one I removed form the 6674A, but one in a 6653A looks a bit different - see picture.

Dave

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PeterW May 16, 2016 10:20 AM
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Hello Drkirkby,

The 6674A you are attempting to repair was manufactured prior to 1995. Many changes have occurred to both the hardware and firmware in that particular instrument. The GPIB interface and even possibly, the front panel itself will require replacement to enable the new display to function correctly with an instrument of that age.

I suggest that the unit be returned to Keysight for repair.

Regards
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drkirkby May 16, 2016 2:37 PM
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Thank you PeteW.
Keysight made me aware of service note 6674A-10, which says the keypad needs replacing with 5040-1735 plus a cable 5080-2261. There's no mention of the GPIB interface in that, but perhaps you know that on a unit of this age, the GPIB needs replacing too. It is clear there's a cable directly linking the GPIB to the keypad.

I have got this working now, by

1) I removed a display (5063-2305) from a 6643A (35 V, 6 A, 210W) . The 5063-2305 worked in the 2100 W 6674A. Unfortunately the display indicated "Serial down". I believe that there was a fault on the 5060-3399 GPIB board, and this is nothing to do with swapping the displays, as the bad display shows some characters, and whilst I could not read them completely, what I can see is consistent with "Serial down".

2) Removed the GPIB board (5060-3399) from the 6674A and put in the same part number (5060-3399) I took from the 6643A.

At that point, the 6674A is functioning. Obviously the 6643A no longer functions, but the 6674A is a much more useful power supply to me, as it is twice the voltage (70 vs 35 V), and 5 times the current (30 A vs 6 A) of the 6643A.

Several large electrolytic capacitors are showing signs of bulging in the 6674A, which is quite common in old capacitors as I am sure you know. So I would not be surprised if the 6674A is not meeting its specifications for noise, but it is at least functioning.

I will order up some capacitors. Some are 6000 uF @ 100 V. The others I will have to remove to see their values. It will take a bit more work, but I think I will get this thing working properly.

BTW, I noticed that there are at least two version of the GPIB board 5060-3399. The one I took from the 6643A looks the same as the one I removed form the 6674A, but one in a 6653A looks a bit different - see picture.

Dave
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6674A replacement LCD does not display - a contrast adjustment issue?

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