I had an almost identical experience restoring my 4342A and certainly echo the comments about not using WD-40 for long term lubrication. I used clock oil for mine. The only other comment I have is about the annunciator lights. The little incandescent lamps in my unit were mostly burnt out or had corroded leads that fell off on being touched. While I was in there I replaced them all with warm white LEDs and there was plenty of room to fit the associated resistors.?

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Morris VK3DOC

Hi,

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Did you make any process with this repair ? I have one unit with the same problem. Thank you.?

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Matthieu?

Hello Yves,

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I just replace the A12 board with another one I bought. All is now working great !?

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I will try to investigation on the board problem later.

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Thank you a lot for you help on this repair.?

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ArtekManuals have the 853A service manual available for download, it's not free but the PDFs they have are excellent quality.

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David

Besides NDAC, is DAV and NRFD behaving properly?? What is the value of ATN at the time the other two bytes are transferred?? And what are the values of those two bytes?

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If ATN is asserted, the bytes are interface control messages, and you can look up the meaning in the "Remote Message Coding" table.? I don't have a copy of the 1978 spec, but in the 2003 spec it is Table 44.

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Besides the hang, do you see any differences on the bus between the two meters leading up to the hang?

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You might find this document a little more digestible. although you still need the spec for the finer details:

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When debugging weird GPIB issues, it's usually worthwhile to monitor all the bus signals.

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-mark

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On Sun, Apr 13, 2025 at 08:08 AM, Steve Hendrix wrote:

A 14mm or 15mm socket, perhaps?

I have also seen 'sockets' that slip over the BNC connector, and have slots that engage the locking posts on the BNC connector. (Those than engage, and hold on the female connector)

You are supposed to apply counter clockwise torque... to rotate the BNC... and not apply the torque to the panel nut (... like you would with a wrench, socket, or nut driver.)

Not so sure about that.

But... I have done it... and it does loosen the nut back enough to allow removing the nut more easily.

I would think... if the nut is really tightly fastened down, the BNC posts would, bend, or tear.

But, it is another way... to perhaps... loosen the nut.

Nice pictures. I have one of these beasts too, so am always interested in info about the guts. Mine all works fine so I never needed to dig in except for pulling the cover to admire the electro-mechanical wonder.

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Before you get in too deep, I'd advise never to use WD-40 as a "permanent" lube in precision mechanisms. It's great for getting things loose and moving again, but it should be washed out afterward and replaced by a light (low viscosity) petroleum-based oil. AFAIK WD-40 uses a vegetable oil base, so it tends to oxidize (and polymerize) over a fairly short time, becoming a thick goo and seizing up what it fixed. It took maybe forty or fifty years for the original lube in the machine to go bad, while the WD-40 might take just a few years. I have proven this to myself a number of times over the years, most recently on some HP8620As where the control knob shafts tend to seize up. WD-40 did its thing just fine, but after two or three years, one of them seized up again, while a couple of others were still OK. The results can vary a lot, depending on the actual conditions of everything, but I'm convinced it will happen inevitably.

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On loose, heavy things from door hinges to tractors, I use it liberally, but I would not trust it for the HP4342A and such. Good luck in getting it all going.

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Ed

Hello All,

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I thought I'd share some pictures from my teardown of the HP4342A Q-Meter purchased from eBay. I wasn't planning on opening it up, however the knobs were impossible to turn so I had no choice.

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The frequency adjustment knob was easy to lubricate with WD-40 after removing the top and bottom panels.? I then lubricated the C and Delta C knobs. This made them easy to turn, but the cable slipped on the grooved knob pulley, indicating that there was still something sticky within the machine. I initially thought the seized shaft was within the variable capacitor. Only after disassembling the capacitor did I narrow it down to the C and Delta C indicator wheels. These were impossible to lubricate in-place as there's no wiggle room to get the lubricant in.

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The bushings must have been lubricated with something which turned very sticky over the years. The bearings all rotated very smoothly.

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The C and Delta C indicator wheels were a pain to remove because of the anti-backlash cable and strip mechanisms. I took plenty of pictures while taking it apart so I had some hope of getting it back together. When rotating the indicator wheels with my hand, the shaft rotated in its housing, indicating a large amount of friction between the wheels and the shafts. Fortunately whatever lubricant was in there was just very viscous and there was no metal-on-metal galling. The result is that I was gradually able to get the shaft to move outwards by applying pressure to the inside end while rotating the indicator wheels relative to one another. After getting just a little bit of penetrating oil in there, everything spun freely.

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Images are here:

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I anyone is interested, I have a bunch I would sell - contact me off line with HPIB in the title

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Cheers!

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Bruce

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hi n4ua, is this still available?

Hello,

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I've managed to snag an HP42851A Precision Q Adapter and the required HP4285A Precision LCR Meter (with option 002) on eBay. Unfortunately, the HP42851A seems to have an EEPROM failure. With the 4285A powered on, I turn on the 42851A and see the following messages in succession:

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- Setup in Progress

- E113: EEPROM Read Status Error

- E116: Q Adapter control failuer

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Images:

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I've never fixed an EEPROM failure before. Is anyone here familiar with this device's EEPROM contents?

The command is hanging at the first byte of the actual command. The meter never issues the NDAC pulse for it. The meter does issue the NDAC pulses for the first 3 bytes transferred, so I know the bus buffer for it is alive.

There are 3 bytes transferred at the beginning of the transaction, with the last of those 3 containing the target address. Do you know what the first 2 bytes are? The IEEE 1978 spec is not the most readable document...

Thanks,

BobH

The docs show the commands in upper case, so that is what I have been using for both meters.

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BobH

I can't see any problems with the sweep in linear mode, Jeff. Although having said that, there's a DC ramp generator at the front end which is sending garbage to the VTO which generates 5-30Mhz from a control voltage of 2.5VDC to 10VDC. These are components of an expansive PLL which is not behaving itself. But I can't tell precisely *which part* of the loop is causing this issue! Where do you even *start* with such a problem in a loop? It could be *any* sub-circuit being the culprit! I'm posting the block diagram of the loop in question herewith....

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Any suggestions welcome!

In a message dated 4/16/2025 12:11:11 PM Eastern Standard Time, paul666@... writes:

Gentlemen,

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About 25 years ago, I acquired an ancient HP8754A VNA plus S parameter test set cheap due to a fault which I subsequently fixed. It's been in mothballs since then, but I pulled it out the other day to see if it was still working (spoiler - it's not!)

With the polar display activated, I can get a dot on the center line at the far right with an 'open' standard plugged into the test set's port 1. I can also get a dot on the center line at the far *left* with a 'short' standard attached to port 1. However, a 50 ohm load displays as a short arc just above where the 'short' position appears when there's a short attached instead of bang smack in the middle of the display where it should be.

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I tried several 50 ohm loads and they all displayed in this same way on this analyzer. However, there was one exception - a high quality load labeled as 50 ohms which displayed as a short arc just above where the 'open' standard trace appears! Like flipping a mirror image of all the other 50 ohm loads and it happened every time! I checked the DC resistance of all the loads and they were all about 50 ohms give or take an ohm - except for the odd one out which measured 54 ohms (must have been damaged at some time I guess). Anyway, this is the one that gives the 'mirror image' result so it's like the analyzer is *way* over exaggerating differences in any attachments between the two extremes of a dead short and an open.

DC voltage checks seem fine. I've scoped the rails and all's well there, too; nice and stable. Anyone have any idea what's going on here?

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- Jinxie

Just a thought...

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Perhaps the two meters are running different versions of firmware and one is being sensitive to upper/lower case?? My 3456A only accepts upper case.

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-mark

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