DISK II PROM P5 replacement

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DISK II PROM P5 replacement

Hi all,
So I have a spare Disk II card with a missing P5 PROM. I thought I could get a TI 28LA22N PROM and program it with my DATA I/O 29b and the Unipak 2.

First I tried the 3410127A.bin file from here:
http://www.applelogic.org/APPLEASICs.html

But it still didn't work, so I tried the 341-0027.bin file from here:
http://mirrors.apple2.org.za/Apple%20II%20Documentation%20Project/Interface%20Cards/Disk%20Drive%20Controllers/Apple%20Disk%20II%20Interface%20Card/ROM%20Images/

and I ended up with an Illegal bit error when trying to program it. It also didn't work.

Does anyone know what I'm doing wrong?

Thanks

Phil

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Re: DISK II PROM P5 replacement

Illegal bit errors indicate that the prom burner has detected a burned fuse that is not supposed to be burned, so you need to try with a different PROM part.

regards,
Mike W.

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Re: DISK II PROM P5 replacement

That's what I thought, so I tried another new PROM and I get the same error.
I have no problem (re)programming either of the PROMs with the first .bin file, only the second one. Strange.

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nama_chari wrote: That's what
nama_chari wrote: That's what I thought, so I tried another new PROM and I get the same error. I have no problem (re)programming either of the PROMs with the first .bin file, only the second one. Strange.

 

Not strange at all, they are not reprogrammable.  Once a fuse is blown it cant be unblown.You cant reprogram a write once device with different data. 

 

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Where did those "new" parts

Where did those "new" parts come from and did you verify they were actually blank before you started programming them?  There are a lot of old stock parts that have gone bad over the years even though they are "new".  There are also a lot of re-marked or outright counterfeit and old used pulls that are being sold as new, especially by offshore sellers.

 

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Beware of buying "onshore" PROMs, too !

In post #5, softwarejanitor wrote:

 

"There are also a lot of re-marked or outright counterfeit and old used pulls that are being sold as new, especially by offshore sellers."

 

Uncle Bernie comments:

 

Beware of "onshore" sellers, too. Some "onshore" sellers source their ICs from the "offshore" sellers while pretending they have them in stock in their own warehouse. IC brokerage has turned into a scam where everybody lists parts they see in the international databases as their own, to attract buyers. When you send a RFQ they ask the guys who listed them for a RFQ themselves, and this may go over several middlemen because nobody actually has the ICs in stock. All the middlemen add their own skim. So in the end you end up with ridicolous moon prices and can't buy these parts. If you buy, you think it's from a local IC broker but you still may end up with Chinese counterfeits, as discussed here:

 

https://www.applefritter.com/content/warning-counterfeit-ds0025-china-oh-no-surprise

 

From time to time - despite I have enough ICs in stock - I "test the waters" and buy a few suspect ICs off Ebay. Alibaba or so I don't use because only in Ebay I can claw the money back (and can get the same junk from the same counterfeiters). And lo and behold, every DS0025 and 6502 I bought off Ebay from any seller located in China (even with "US stock") turned out to be counterfeit. Oh, in every case I got my money back, and in most cases I even could keep the counterfeit parts because the seller does not want to pay the return postage, so they told me: "you can keep them". So I get ICs for free ! The fake 6502 typically are re-stamped (laser engraved with the Rockwell logo) CMOS 6502 of various types, so they may be useful, except in the Apple-1, and the fake DS0025 are re-stamped Renesas MOSFET gate drivers which don't work in an Apple-1 and would be overstressed anyways, they are specified for absolute maximum supply of 15V (for 12V automotive being their main market) while the Apple-1 has 20V (+5V/-12V) on the DS0025 socket.

 

With PROMs the situation is even worse because many IC brokers are incompetent and don't know (or don't care)  that PROMs are programmable parts which have zero value once programmed. Same level of incompetence and "don't care" can be found with character generators. I know places where they have thousands of character generators in stock but they only list the first part of the part number (the character generator family, like RO-3-2513) but they don't list the second part of the part number, which defines the character set within. There are lots of Signetics 2513N out there (and the greedy brokers want $150-$200 a piece because some have paid that price on Ebay for the ones with a 76XX date code used in the original Apple-1) but these which are still available from IC brokers don't have the CM2140 character set in them, so they are essentially worthless. How I know ? My friends and me have asked every broker who listed Signetics 2513N in the world. Every. Single. One. This took us 4 months. All with the wrong characters sets. So let go of any hopes. They are gone !

 

It is very hard to find a good IC broker who knows what they are selling, who has the parts in stock in their own warehouse, and knows the provenance of these ICs, that is, the whole story of origin and chain of custody they had. If they have never left the USA or Europe, they are probably not counterfeit. If they ever have been near or in China, they most likely are counterfeit. So buyer beware !

 

The whole situation with these vintage ICs gets worse every day. This affects both Apple-1 and Apple II restoration or cloning projects, so I think we kann keep this post in the Apple II forum. The very early Apple II did use the same character generator as the Apple-1, which now is unobtainum. Some plain vanilla TTL also are running out - but the 74LSxxx TTL used in the Apple II still are available.

 

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