Macintosh SE/30 replace processor MC68030RC16B to MC68030RC30C

[Plottem]

Good morning, I am restoring a Macintosh SE/30 that I received as a gift. The case is the following, the motherboard did not have the Motorola MC68030rc16 shock type processor (someone removed it to sell the gold) I bought the same one but the seller sent me a MC68030RC30C, instead of the MC68030rc16B, I assumed that there would be no problem in that in instead of 16mhz I had 30mhz. I recap the board and got it working. The equipment works but the resistor R29 (12 Ohm, 2w) of the analog board gets very hot!!! and I'm afraid it might burn. Do you think that the increase in temperature in this resistor could be due to the difference in MHz between the original processor and the one that I have installed? Greetings

 

[Phipli]

Good morning, I am restoring a Macintosh SE/30 that I received as a gift. The case is the following, the motherboard did not have the Motorola MC68030rc16 shock type processor (someone removed it to sell the gold) I bought the same one but the seller sent me a MC68030RC30C, instead of the MC68030rc16B, I assumed that there would be no problem in that in instead of 16mhz I had 30mhz. I recap the board and got it working. The equipment works but the resistor R29 (12 Ohm, 2w) of the analog board gets very hot!!! and I'm afraid it might burn. Do you think that the increase in temperature in this resistor could be due to the difference in MHz between the original processor and the one that I have installed? Greetings

You should be fine with your 30MHz processor, if anything, it will use less power and run cooler.

I suspect the resistor is meant to run that hot.

 

[Plottem]

You should be fine with your 30MHz processor, if anything, it will use less power and run cooler.

I suspect the resistor is meant to run that hot.

Thanks for your answer, the temperature gets too high, you have undone the silicone that holds the fan wires, and these are getting shiny, and it smells like burning.

 

[Phipli]

Thanks for your answer, the temperature gets too high, you have undone the silicone that holds the fan wires, and these are getting shiny, and it smells like burning.

I suspect it isn't because of your CPU, unless the CPU is faulty. Try powering on without the CPU installed and see if the resistor still gets hot. If it does, search near the resistor (for things electrically connected) for a part that has shorted.

Can you desolder one side of the resistor and measure if it has the correct resistance?

 

[Plottem]

I suspect it isn't because of your CPU, unless the CPU is faulty. Try powering on without the CPU installed and see if the resistor still gets hot. If it does, search near the resistor (for things electrically connected) for a part that has shorted.

Can you desolder one side of the resistor and measure if it has the correct resistance?

Good idea!! I'll do the test! thanks!

 

[Melkhior]

I bought the same one but the seller sent me a MC68030RC30C, instead of the MC68030rc16B, I assumed that there would be no problem in that in instead of 16mhz I had 30mhz

You probably know that already, but for the sake of completeness: your new CPU is _capable_ of 30 MHz operation, vs. the original one that would only be rated for 16 MHz for whatever reasons. However, in the SE/30, this CPU will still _run_ at the 16 MHz, as dictated by the CPU clock. This is totally safe from the CPU point of view (as mentioned by @Phipli, if anything it will save power/energy as the 30-MHz rated CPU is likely running on less power/cooler than the 16-MHz rated one), but it doesn't help with performance.

 

[GreenBar0n]

Can I use a Motorola MC68030RC33B in an SE/30?

https://www.ebay.com/itm/371776928912.

The CPU my SE/30 came with was a XC68030RC16B, which seems to be very rare and I can't find an exact replacement.

 

[Phipli]

Can I use a Motorola MC68030RC33B in an SE/30?

https://www.ebay.com/itm/371776928912.

The CPU my SE/30 came with was a XC68030RC16B, which seems to be very rare and I can't find an exact replacement.View attachment 93572

Yes you can - behaviour will be identical as far as it matters.

The speed is just the grade - the part is the same, just approved to be operated at higher speeds... In computers that run at higher speeds.

Plug it in and enjoy.

 

[GreenBar0n]

Yes you can - behaviour will be identical as far as it matters.

The speed is just the grade - the part is the same, just approved to be operated at higher speeds... In computers that run at higher speeds.

Plug it in and enjoy.

Thank you so much!

 

[larwe]

Can I use a Motorola MC68030RC33B in an SE/30?

https://www.ebay.com/itm/371776928912.

The CPU my SE/30 came with was a XC68030RC16B, which seems to be very rare and I can't find an exact replacement.View attachment 93572

The XC prefix on moto parts means preproduction/early access samples. I vaguely recall Apple and one other vendor at least put XC parts into production computers because they got super early access and were satisfied with performance/stability.

 

[GreenBar0n]

The XC prefix on moto parts means preproduction/early access samples. I vaguely recall Apple and one other vendor at least put XC parts into production computers because they got super early access and were satisfied with performance/stability.

Thanks for the reply. On ebay there are a few loose SE/30 boards for sale, from 1987-1988, early SE/30's like mine, where the boards look new still but they all have the simasima pattern and they all have the XC68030RC16B CPU's.

I am wondering if the XC, like you said, was an early chip that fails early too, as they switched to the MC68030RC16B not long afterwards.

I have taken all of the steps provided by the excellent Simasima Repair Guide, found here:

Macintosh SE/30 Vertical & Horizontal Bars on Display "Simasima" Repair Guide

Hello everyone, This has been a long time coming... presenting the Macintosh SE/30 Vertical & Horizontal Bars on Display "Simasima" Repair Guide!! 🎉 This is a FREE downloadable PDF document (~55 MB) filled with high-resolution pictures and technical details. You can find this PDF file...

tinkerdifferent.com

- to troubleshoot the issue - and my board and all the traces/chip functions seem to be in perfect working order, except the CPU 'walking the bus'; not one ROM Address line has a clean square wave.

I should have the new MC68030RC33B next Monday, I'm really hoping this is the issue - it almost has to be at this point after all of the troubleshooting.

Thank again for the info!

 

[croissantking]

I’ve never heard of any problems with 68k Motorola chips with XC prefixes. I think most of the ones Apple shipped were labelled XC, since the validation process could take quite some years.

 

[larwe]

Thanks for the reply. On ebay there are a few loose SE/30 boards for sale, from 1987-1988, early SE/30's like mine, where the boards look new still but they all have the simasima pattern and they all have the XC68030RC16B CPU's.

I am wondering if the XC, like you said, was an early chip that fails early too, as they switched to the MC68030RC16B not long afterwards.

I very much doubt it. I mean, sure it's a weird coincidence what you're seeing, but lots of equipment was shipped with XC parts. Is it possible that there are bad batches? Sure, compare date codes on the bad boards and see if they're all clustered. But I really don't think it likely that these are inherently bad parts, it's just an interesting note that they are _earlier_ parts. Gathering the QA data to move them from XC to MC status took time, that's all.

 

[larwe]

I’ve never heard of any problems with 68k Motorola chips with XC prefixes. I think most of the ones Apple shipped were labelled XC, since the validation process could take quite some years.

I don't recall seeing XC68000s (even the Lisa boards I've seen had MC68000s) but for sure I've seen plenty of XC030 and XC040 CPUs in Apple gear. I, too, have not heard of any systemic problems with the parts, it's just an interesting historical note.

 

[GreenBar0n]

I should have the new MC68030RC33B CPU shortly, I'll follow up when it arrives.

If in fact my XC is bad, what would have killed it?

Why would Apple switch to the MC68030RC16B, if the XC was good enough? What's the actual difference?

Summary of troubleshooting and current issues with my SE/30 board, CPU not 'walking the bus':

Macintosh SE/30 M5119 - Year long troubleshooting battle

Hi all, Really glad to have found this forum recently and specifically the Simasima Repair Guide posted here, much thanks for that! I purchased this SE/30 around this same time last year and recapped every board in the unit, also removed UE10 and reinstalled it, fixing all of the broken...

tinkerdifferent.com

 

[Phipli]

If in fact my XC is bad, what would have killed it?

I have never seen a single failed 68030, I have quite a few. You're over thinking things.

Has the board been recapped by the way? That is a requirement for SE/30s as the capacitors they were built with leak a corrosive fluid over time. If it hasn't been done, you might want to talk to Amiga of Rochester if you're in the US. They'll recap and repair.

 

[GreenBar0n]

I have never seen a single failed 68030, I have quite a few. You're over thinking things.

Has the board been recapped by the way? That is a requirement for SE/30s as the capacitors they were built with leak a corrosive fluid over time. If it hasn't been done, you might want to talk to Amiga of Rochester if you're in the US. They'll recap and repair.

CayMac Vintage on Youtube has experienced a bad XC CPU, in a video of his about 7 months ago.

Every board in this unit has been recapped. I included a link to a thread showing everything that's been done to it, above.

The CPU is not walking the bus, I have a scope and am looking at every Address line in the ROM slot, A2-A31, there is no clean square wave with or without the CPU inserted:




This thread details all that has been done so far in a brief summary:

Macintosh SE/30 M5119 - Year long troubleshooting battle

Hi all, Really glad to have found this forum recently and specifically the Simasima Repair Guide posted here, much thanks for that! I purchased this SE/30 around this same time last year and recapped every board in the unit, also removed UE10 and reinstalled it, fixing all of the broken...

tinkerdifferent.com

Or a longer thread here:

Thread 'Macintosh SE/30 M5119 - Restoration'

Dec 15, 2024

This SE/30 wasn't far from me, so the shipping was cheap. The seller is not a tech, more of an estate hunter/flipper, with a 100% feedback rating. Took a chance on this one (seller's pics, should be here Wednesday).







It looks pretty good on the outside, but you never know what's lurking within. Schrodinger's batt. (lithium vial).

For $250 I rolled the dice, it was reported as 100% untested. Win or lose, I should know soon.

If it has the Sony CR-44 PSU, it's a black IEC socket and switch?

• GreenBar0n
• Replies: 188
• Forum: Compact Mac

 

[Phipli]

CayMac Vintage on Youtube has experienced a bad XC CPU, in a video of his about 7 months ago.

That doesn't make it a regular occurrence. Good luck.

 

[GreenBar0n]

Am I still overthinking this, or is there another answer as to why my particular CPU is not 'walking the bus'?

 

[cheesestraws]

It is entirely possible your CPU has failed. But if it has, it is not because it is an XC part, it is because in time all things will fail. The fact that your specific one that has failed has XC on the top of it is not really meaningful here, it's just noise.