Replacing 80xx series ICs?

looks like the 8279 has an internal OTP EPROM.

Might be tough to find a replacement

Bill

Opps my bad, looks like the 8279 is a programmable keyboard I/O chip. So you should be able just to pop one in. (assuming that's what's wrong with the device)

Bill

Thus spake William at MyBlueRoom:

This is what I need help determining. If this is a "production programmed" device (burned at time of manufacture), it's a deal-killer for my customer -- finding a programmed replacement is pretty much not going to happen.

But if this is a "dynamically programmed" device (ie, counters are loaded at run time and reset by external devices), I presume that off-the-shelf it will replace the suspect one in the machine.

Is the 8279 a one-time programmed device?

Thanks,

Thus spake William at MyBlueRoom:

Oh, you answered my question while I was posting another message to ask you this very question. (Such is the down-side of asynchronous communications!)

Thanks!

It appears not to be.

Graham

Hi,

All those parts are still available in the market.

Pieter

No, it is just a peripheral with some registers to 'program' its function.

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I do believe that the 8279 is not a programmed device. I could go look it up, but that would take work! The 8279 was often used for keyboard input and display output. The display will be multiplexed. There should be a BCD to seven segment converter chip that drives all of the displays in parallel. Then each display will have a power transistor that switches Vcc on for that display. The power transistors on signal is sync'd to the BCD word so that the data appears on the correct display. Make sense?

It seems to me that everyone is "going off on one", before the OP has applied at least basic proper fault finding techniques. Before going in shotgun and replacing parts that - trust me - seldom if ever go faulty, you should first check that the 5v supply is absolutely good - voltage, ripple AND noise, that the reset generator is working correctly, and that most importantly, the system clock generator is running, and producing a correct amplitude and frequency, signal. Also that any following clock distribution buffers are working.

If none of those checks turn up the problem, and in at least 80% of cases on this old simple logic, they will, then the next move is to download a datasheet for the display controller, and figure why it's not driving the displays. The required inputs are not many, and not complex, and require only a 'scope to verify.

From years of experience repairing electronic equipment, I can tell you that blanket replacement of components in the fond hope of hitting the right one, is about the worst approach that you can take, and likely to result in more problems than the probably simple one that you had in the first place.

Arfa

Perhaps the local fea market. Look for old 8 bits micros. The 8085 is an old 8 bits micro, so there must be an EPROM somewhere. Unfortunately, EPROM data are not designed to last for 20 years. It's amazing to have lasted so long already. My first bet is the EPROM losing contents. Unless you have a copy of the data somewhere, forget it.

Sound like this is a frequency counter/display or something. A single chip micro (AVR or PIC) can do the same.

It sounds as though the instrument is a Digital Readout display associated with machining or other production equipment. I don't have much advice for troubleshooting other than what's already been suggested by Arfa. It's been too many years, and too little practice since my training in these types of circuits. I have a completely dead Anilam DRO display, and I've had difficulty understanding the circuits even though I have a schematic.

If you proceed with IC replacement, check any datasheets you can find to confirm that the operating voltages of replacement parts are the same.

Newer used DRO systems are plentiful, depending upon your searching abilities. If the linear encoder scales used with the DRO display unit are the commly used 5 volt TTL squarewave types, you could possibly just replace the display unit with one that's compatible.

Finding a suitable replacement will probably be a little tougher if the DRO display also has outputs for interfacing with NC or CNC machine controls, but numerous displays have various optional modules to convert inputs to outputs.

There are numerous surplus suppliers of older ICs in the U.S, and more semiconductor sellers are gradually appearing on eBay.

Cheers WB ..............

DaveC wrote:

Reducing the supply voltage a bit (was it? or increasing?) might still recover the data.

Thomas

Do you have any data which supports this claim?

Most manufacturers claim 100 years or more at normal temperatures.

Best regards, Spehro Pefhany

Yes.

Best regards, Spehro Pefhany

All of those parts were originally from INTEL. NEC was a second source. What type of RAM does it use?

...also had good experience with carefully cooling the EPROMS during readout...

Erik.

? "linnix" ?????? ??? ?????? news: snipped-for-privacy@z34g2000cwc.googlegroups.com...

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When you say EPROM, you mean those chips with the little transparent window that could be erased with special UV light?If yes, could this just happen with long exposure (many decades) to normal sunlight (even if dim in the bowels of the machine).I strongly doubt though, that you could find nowadays labs with the UV light and programm devices to programm (again) those chips, now that flash chips are so common and cheap (EEPROM). Are there any chips with the characteristical transparent window?

-- Tzortzakakis Dimitrios major in electrical engineering,freelance electrician FH von Iraklion-Kreta, freiberuflicher Elektriker dimtzort AT otenet DOT gr

People who made these claims in the 80s are mostly retired or dead.

Can't find any typical EPROM (2716 or 2732) used in the 80s. A newer one like AT28C16 says data retentions of 10 years. If you want to bet $1 per year, we can find an independent engineer for verification.

There are still lots of devices in older stocks available. And for many devices replacement parts have been created by others.

I just did a quick search and found hundreds of the D8085HC of NEC at my contacts. It is expensive to get 1 part due to the shipment costs, but it is possible. I havent searched the other partsm, but I am certain they are available too.

Pieter