Re:-

I wonder if I could pull them, read them out and reprogram onto new chips.? If one is on the edge that might fix it.? EPROMs do go bad...


Good, if you can be sure you read the EPROM as originally programmed, not while it is in it's faulty state.

As others have said, it could also be a bad bus transceiver/buffer, either not pulling it's output all the way up or down, or "leaking" significantly when it's output is supposed to be in it's high z state, or it's input thresholds have changed.

A memory address decoder problem can cause mayhem too, for example two chips intermittently being selected at the same time will cause trouble.? One of the more difficult faults to trace.

I'd get a decent 'scope, trigger it from a bus access qualifier related with instruction fetching, and look for bus contention, or "weak" signals.? (Analogue 'scopes are often better at that sort of work.? DSO's often lie like a cheap watch, unless you take "Greate Care" to ensure you have one with sufficient sampling rate, and trace memory to catch the fastest signal on the board in full fidelity, often the CPU clock, but not always.? Even then some miss glitches.

If the general logic is all on sockets, just "refreshing" the IC seating can often help, but doing that one chip at a time takes too long, so general the whole board is done and tried again.

At worst, the "fault" might then be permanent, and may be easier to track down.

I learnt that, when I used to fault find to component level on the old Data General Nova 3 and 4 series minicomputers "Back in the day", as well as the third party peripherals they used. Disc controllers and a semi autonomous Mass Spectrometer I/O board.? Often with some 200 TTL IC's on them!? (15 inch square multi-layer boards!)

One particularly troublesome mixed signal board I recall, over many days of odd bits of spare time, to prove a point, I removed each analogue and digital IC and it's socket in turn, and refitted that IC directly soldered to the board in the same position whence it had come from.

The exception was any IC that had a direct connection off-board.? They got expensive turned pin sockets. ? ALL the problems then vanished and never came back!? The result was so profound (the board in question had been officially scrapped as BER. ) The company started making those boards in that style, even using the same style turned pin sockets!? Product reliability with the end customers went up enormously, and our in house service workload reduced to sensible proportions.

Regards.

Dave 'KBV

On 12/14/2018 5:29 PM, Yves Tardif wrote:

> Hi,

> I bought a 3577A several years ago and I had a few times the UNLOCK

> message that appeared on the screen with a BEEP sound and lasted less than a second.

> I thought then that it was the instability of the PLL 10MHz when

> powering on, and the problem disappeared after a few minutes.

> Over time, the problem was more common and seemed independent of the

> temperature or operating time of the device. But that did not prevent

> me from using it.

> Recently, the problem became more serious, and the UNLOCK message

> appeared with the indication of a possible failure on the A5, A6 or A7 PCBs.

> So, I decided to look for the problem so I checked the A5, A6 and A7 PCBs.

> The power supplies were stable and rated, the problem was that the

> phase detector was no longer receiving feedback from the VCO.

> The circuit is a little complex, but I realized that everything was

> pointing to the synthesizer, a custom HP circuit.

> I noticed when scanning the VCO spectrum that sometimes it stops for a

> fraction of a second or more without UNLOCK and then suddenly continues scanning.

> On the screen the sweep continued, or sometimes stopped like the VCO.

> Several other more rare symptoms were added like, the frozen screen

> and a PRESET solved the problem, unwanted characters on the screen,

> message ERROR SYTEM # 24 ...

> I thought then maybe the processor card was the cause of the problem.

> I had already checked the test points at the main power supply and

> everything was ok. So, I put an oscilloscope in ROLL mode and monitor

> the different voltages for a period of time where there was the

> problem ... everything was stable.

> So, I decided to monitor the voltage all over the motherboard, and

> finally, I discovered that during the intermittent problem, + 5V

> suddenly decreased during the period, as low as + 3.9V.

> The + 5V of the motherboard comes from a pair of AWG12 or AWG14

> soldered wire that goes to the main power supply where it connects via

> a connector (it passes 10A by this link).

> The connector was not damaged, no sign of overheating.

> After several unsuccessful attempts to repair this connector, I

> decided to directly solder the pair of wires from the motherboard

> directly to the power supply.

> Since that time, all the intermittent problems that they have disappeared.

> My 3577A has never worked so well.

> For those who have a 3577A and have this kind of intermittent

> behavior, the J8 connector may be the cause.

>?

> Yves

>?

?

? "You will own nothing and be happy".

? Explanations of this, why it is bad, why it is unnecessary, and why people should avoid it are met with blank stares.? The same kind of blank stares that result from people being told about "free" online services, the fact being that if you receive value for free, you are the product.? People just don't get it.

? People are generally clueless.? I've all but given up trying to save them from their own stupidity.? You can only yell "you are heading toward a cliff!" for so long before it becomes tiresome.

?????????? -Dave

Bad trace memory should not give illegal instruction traps. Assuming the trace memory is solely used to store data, and is not (also) used to store executable code in. Unless, of course, something is corrupting the data path, common to both instruction and data transfers.

You have returned the suspect RAM chips to their original location?

Bad trace memory should not give illegal instruction traps. Assuming the trace memory is solely used to store data, and is not (also) used to store executable code in. Unless, of course, something is corrupting the data path, common to both instruction and data transfers.

You have returned the suspect RAM chips to their original location?

On 12/15/24 14:31, Frank Mashockie via groups.io wrote:

This also goes back to right to repair and the lengths companies from all industries are going to 'protect' IP.? Which I still can't believe there were people in this group arguing for company practices like this in the last discussion I was involved in on this topic.
Also, I wouldn't underestimate your need for instrument support with newer equipment.? I work in the biotech industry as an in-house Lab Instrument Engineer.? And for newer equipment, manufacturers are locking down the equipment so that any time you need to perform a repair you NEED to utilize add-on software that allows a manufacturer tech to remotely access the instrument to resolve the issue.? This isn't a feature, it is required!? I suspect any manufacturers of equipment not under scrunity of recent changes to copyright law (ensuring that customers get access to service codes, passwords, etc) will continue these kinds of practices.? That includes electronic test equipment.
I tell my colleagues the same thing that others have said here. Unless you really need the newest equipment because it encompasses technology that will truly advance our science, go with something that is 15-20 years old (or more).? You'll be able to service it without the expensive service contracts these OEMs push in lieu of supporting customer/3rd party repair.? This will keep upfront AND long-term costs way down.

? "You will own nothing and be happy".

? Explanations of this, why it is bad, why it is unnecessary, and why people should avoid it are met with blank stares.? The same kind of blank stares that result from people being told about "free" online services, the fact being that if you receive value for free, you are the product.? People just don't get it.

? People are generally clueless.? I've all but given up trying to save them from their own stupidity.? You can only yell "you are heading toward a cliff!" for so long before it becomes tiresome.

?????????? -Dave

Buss errors and illegal instructions smell like bad RAM, ROM or maybe both. Or a bad bus transceiver maybe. Can be other things too, anything dodgy in address decoding, address bus or data bus can also do it ??

This also goes back to right to repair and the lengths companies from all industries are going to 'protect' IP.? Which I still can't believe there were people in this group arguing for company practices like this in the last discussion I was involved in on this topic.
Also, I wouldn't underestimate your need for instrument support with newer equipment.? I work in the biotech industry as an in-house Lab Instrument Engineer.? And for newer equipment, manufacturers are locking down the equipment so that any time you need to perform a repair you NEED to utilize add-on software that allows a manufacturer tech to remotely access the instrument to resolve the issue.? This isn't a feature, it is required!? I suspect any manufacturers of equipment not under scrunity of recent changes to copyright law (ensuring that customers get access to service codes, passwords, etc) will continue these kinds of practices.? That includes electronic test equipment.
I tell my colleagues the same thing that others have said here.? Unless you really need the newest equipment because it encompasses technology that will truly advance our science, go with something that is 15-20 years old (or more).? You'll be able to service it without the expensive service contracts these OEMs push in lieu of supporting customer/3rd party repair.? This will keep upfront AND long-term costs way down.