Questions about an LCIII to LCIII+ overclock mod on machine with MC68030FE16B installed.

[ClintonGoodfellow]

Hi,

I've always thought for some reason that my old LC was a III+ but it turns out its a standard 25mhz LC III.

Disappointed but I remembered about the resistor mod, so I thought I'd look into it.

Following this tutorial - http://www.applefool.com/clockchipping/lciii.html , the mod is very straight forward, but it does raise a couple questions.

From looking at the logic board I can see there is a MC68030FE16B installed (pic attached) instead of the -FE25B I expected to be there. The machine reports as a 25mhz machine even with this apparent 16mhz processor installed.

The question is, if I moved the jumper (0ohm resistor) on the board to enable 33mhz would this work with the installed processor? Also should I be looking to put a heatsink on some of the chips, will there be excess heat?

I'm also wondering why this processor is on the board as its clearly an LCIII logic board, maybe its been factory modified by Motorola due to a shortage of the 25mhz ones? Who knows?

Hope you folk can shed some light on this, as I'm not sure whether to test it or not.

Cheers.

 

[Nixontheknight]

I've been good so far without a heatsink , but I'd very much recommend it

 

[ClintonGoodfellow]

Just found this thread which shows a 16mhz marked processor in an LC III. It doesn't say however if it can be OCed as usual?
- https://68kmla.org/bb/index.php?threads/mac-lc-iii-16mhz.20328/

I have also attached a closeup of the processor.

 

[Byrd]

I've a Sonnet SE/30 33Mhz accelerator that is the same 16Mhz part - I get the feeling for a time Motorola sold many 16Mhz marked CPUs that were completely reliable at 33Mhz and distributed as such. The accelerator I have is displaying evidence of CPU failure though, I intend to replace it with a 33Mhz QFP part next which is available cheaply.

 

[ClintonGoodfellow]

Hi thanks for the replies.

So possibly that Moto just sold the same part with diff printing?

I'll just go ahead with the mod and pop a heatsink onto it for good measure as Nixontheknight suggests. Is it worth putting one on the video chip also?

Do you think the cpu failure is due to the chip being pushed, or just age and use? If my one fails, I can swap it as you say, so I'm not majorly concerned.

 

[Siliconinsider]

Look at the mask revision, the smaller the lithography the less heat/faster you can get.
D66C is 1.0µm so they should fare well with overclocking.

 

[Nixontheknight]

Hi thanks for the replies.

So possibly that Moto just sold the same part with diff printing?

I'll just go ahead with the mod and pop a heatsink onto it for good measure as Nixontheknight suggests. Is it worth putting one on the video chip also?

Do you think the cpu failure is due to the chip being pushed, or just age and use? If my one fails, I can swap it as you say, so I'm not majorly concerned.

I’d recommend a heatsink on the video chip as well, and put one on the FPU if you plan on installing the FPU

 

[ClintonGoodfellow]

Thanks for the advice folks, I'll give this a go shortly and see how I get on!

I have seen an 68882 (MC68882FN40) FPU for very little, so I'll likely install it. Should work alright?

 

[Nixontheknight]

Thanks for the advice folks, I'll give this a go shortly and see how I get on!

I have seen an 68882 (MC68882FN40) FPU for very little, so I'll likely install it. Should work alright?

any 68882 should work in the LC III, but be warned about fake chips

 

[ClintonGoodfellow]

Thanks for the heads up, I didn't realise that was a thing with these.
I'll make sure it's a trusted seller just in case.

 

[Siliconinsider]

Pretty much all 40MHz 68882 will be fake. I don't think Motorola made them in PLCC package (33MHz was the highest). If it's laser engraved it is very likely fake as most of the production was made with silkscreen printing.

 

[ClintonGoodfellow]

The same ebay seller im looking at has a 40mhz one laser etched as you suspected and a 33mhz one silk screened. See below

33mhz 68882

40mhz 68882

 

[Siliconinsider]

The 1993 date code on the 33MHz one matches, but who knows what you'll get...
The 2012 date code on the 40MHz was when Motorola long became Freescale, 100% fake.
Photos can be for indication purpose only, very common on ebay.

 

[ClintonGoodfellow]

Amigakit list both a 25mhz and a 40mhz 68882. I’ve bought loads from them over the years and I highly doubt they would sell something they haven’t tested. Will either work or should I specifically be looking for a 33mhz one? I take it the number is the maximum rated speed?

 

[Byrd]

Hi Clinton,

I bought my QFP 33Mhz CPU from here, can confirm it's legit and came in the chopped up plastic housing as pictured

1PCS MC68030FE33B QFP-132 ENHANCED 32-BIT MICROPROCESSOR | eBay

Find many great new & used options and get the best deals for 1PCS MC68030FE33B QFP-132 ENHANCED 32-BIT MICROPROCESSOR at the best online prices at eBay!

www.ebay.com.au

JB

 

[Siliconinsider]

It's not because they have been sanded and laser remarked that they will not work, it's just that you don't know what you get at all and the markings are not original. They are remarked from whatever stock, speed grade and mask they have, to make a product that looks new and a new stock that is homogeneous. Also there's a big demand for 40Mhz FPUs.
I honestly have never seen a genuine Motorola 40MHz PLCC 68882 and I have been collecting chips for 20 years.

Amigakit has photoshopped their photo not to show the speed.

 

[Franklinstein]

I bought a few of the China-origin 40MHz 68882s a while back. Fortunately they are, at least, actual working 68882s; I've heard of people getting chips with the same PLCC package but that are either non-functional or entirely different internally. I don't plan to run these any faster than 33MHz so it shouldn't be a problem.

As for the mismatch in speed in OP's CPU, it's not uncommon. I have an LC 520 board that has a sticker applied to the CPU. The sticker, complete with Motorola logo, identifies it as a 25MHz part (which is the stock speed of an LC 520) but the sticker came away a bit and underneath are markings that identify it as a 33MHz part.
Sonnet's web page also has a section titled something like "why is my CPU marked as lower than its advertised speed?" and essentially the reason is that these parts are binned at a certain speed for a customer but the customer cancels. Later another customer orders some chips, so the cancelled chips are then re-qualified and/or re-badged for different speeds (slower or faster as the case may be).

 

[Fizzbinn]

I ordered this "MC68882FN33A PLCC-68 RH" from eBay for my Duo Dock. Just received:



So the second line "1C12R" is the mask and in the third line "93" is the year made? Is there a doc somewhere on the Internet (or maybe Way Machine) with a list or 68882 masks/die sizes?

Secret decoder ring:

MC68882FN<Speed_rating><Revision>​

<Mask>​

<4_characters_meaning?><Year_made><2_digits_week_made?>​

 

[djhaloeight]

My LCIII+ has a 68030 CPU marked 33 but it only ran at 25MHz. @max1zzz is in the process of finishing up transferring all of its chips and parts to one of his new production LC III boards, and I had him do the resistor mod so it runs at 33MHz like it should. Can’t wait to get it back

 

[ClintonGoodfellow]

Hi,

Got a bit of time the other day to perform that overclock mod. Took about 5mins and worked perfectly. Machine showing up as 33mhz. Is there anything else I should be aware of?

I will just need to order some heatsinks. However I have also realised that with the NIC installed in the case, it doesn't leave much room for a heatsink as it obscures the processor. Are there smaller NICs available?

Regarding the 68882, I went for a rummage in my storage and found a spare amiga 1200 expansion that contains a PLCC 68882 at 33mhz. I have attached a picture, surely this will do rightly for the LC?

Is there a specific app available that I can use to test the fpu or display info about it?

I'd still like to pick up another though, so if anybody knows a reliable source, let me know!

Cheers folks.