Microbotics Starboard 2 for A500 HELP

[Metalguy66]

Hey TjLaZer... Nice to see you on the Amiga forums..

Hey listen.. Since we know the A1000 starboard doesnt need an extra PSU, and all that RAM is standard 5v parts, we're pretty sure that it needs a 5vdc supply..

 The question is, are there any transformers, rectifiers, or regulators in there? If so, email me and we'll discuss how to determine an appropriate power input type/range... If not, then all you have to do is figure out where to put +5v and Ground.

First, you should look it over real good and see if theres any jumpers to allow it to draw power from the A500.

If no luck there, just get an ohm meter and check from the VCC pin of one of the chips to the power connector. Whichever pin of the power connector reads near zero ohms (like less than 10), is your +5v input. Whichever pin reads near zero to the ground plane of the board is ground..

Unless that thing has provisions for powering a drive inside of it, it shouldnt need any other supply voltages.

[Metalguy66]

Heh. I havent noticed that at all.. And unless that starboard is an EXTREMELY inefficient design, I find it hard to believe, unless (as I stated earlier) its actually spinning a hardisk inside the unit off the same power..

My A500+ has a 68030@50mhz, 68882@50mhz, 32 megs of ram, PLUS a GVP sidecar with 8 more megs of ram and a 3.5" desktop hardisk, all running off the stock A500 psu..  and no problems whatsoever..

My other A500+ has the same GVP sidecar, also with 8-megs of ram and a desktop hardisk, and it uses a single stock A500 PSU..

My Rev 6a A500 has a supra 500XP sidecar with 8 megs of ram and a desktop hardisk inside it, and (yep, you guessed it) runs off the stock A500 PSU..

Ive never had any problems running any of these machines this way.. In fact, Ive noticed that some PC power supplies cause a noticeably degregation of the audio clairity/quality on A500s..

Anywayse.. If theres no jumpers to enable "shared power" in that thing, then I'd reccomend going with a second PSU for it...  That old DIP package DRAM is pretty power-hungry by comparisson to later chips used on SIMMs.. So its quite possible that it does need some serious "juice" to run it...

But the A500 PSU does have quite a bit of "extra capacity".... It has no problem running the A500, an accelerator, and most modern low-powered add-on devices..

[Metalguy66]

BuzzBrain wrote:

I asume you use the orginal external power for the GVP devices?
So, the SCSI/IDE disk and the 8mb memory use own power?

You assume wrong.. EVERYTHING on all 3 systems runs off of the A500 power supply. I dont use the GVP external power supplies at all.. In fact, I dont even know where they are.. Ive never used them. The stock A500 PSU runs everything just fine.. and for hours on end... and has for years..

[Metalguy66]

doesn't the GVP HD8 sidecar need to be modded to close 4 jumpers to allow it to draw power from the A500?

You have to close 2 jumpers on the A500HD+ board yeah.. I really dont consider that a "mod" since GVP provided the on-board circuits to power the thing that way, and jumpers to enable the feature.. I think they knew the SCSI controller & DRAM would run "no problem", but included the external PSU as a "CYA" measure due to the fact that most hardrives at the time were still relative "power hogs" when compared with more modern drives..

so A500 power is not a problem  just from the sounds of it, getting it into the starboard is whats needed.

Well, I have done some DRAM circuit design in my time.. And if the Starboard is making it's 2megs with old 256k x 1 DIP package DRAMs, it's gonna suck some juice..(It takes 64 chips to get 2 megs this way). Probably 750ma or better... If it's using 256k x 4 (only 16 chips), it's much less.

In the case of the GVP, the newer/smaller package DRAMs used on the vast majority of 30 pin SIMMs are much less "power hungry".. A 4meg SIMM that uses eight 1meg x 4 DRAMS only draws about 50ma...

(and yes, paula does need the -12v line otherwise you get horrible crackly audio... which doesn't seem to be what it should be on all PC PSUs - seen a solid -4v on the -12v line. looked like no problems for the PC it powered, but for an amiga, diffferent story.)

I bet you are exactly right about that.. I assumed it was just noise on the power circuits in general, but I did not bother to measure/scope any of the circuits. When I noticed the problem, I just got another stock A500 PSU which fixed the problem..

[Metalguy66]

Somehow I don't believe you. Your "stock" A500 PSU is probably a custom one. I had/still have an A500 with the TRUE stock PSU, and it could BARELY power the 512K belly memory expansion and one external floppy. NOTHING else. Period. End of discussion. New and more powerful PSUs for the A500 did a brisk business in those days as the stock supply was good for nothing. Wherever you got your A500 from, the dealer almost certainly swapped your PSU for something more powerful.

The stock supply for the A1200 was even worse. Go to any Amiga magazine or any Amiga site and you'll see the same thing - those stock supplies couldn't power virtually anything at all. It's why things like the GVP had their own supply in the first place. They wouldn't have put it on there if it wasn't necessary.

I have 4 A500 PSUs.. They came from all different sources and I use them interchangably between systems with no problems whatsoever. They all bear the same part number (312503-01), but one is noticably heavier than the other three.. And interestingly, the heavier one is rated at less current (4.3a) on the 5v circuit than the other three which are rated at 4.5a...  The 12v circuits on all 4 are rated at 1a, and the -12v circuits are all rated at 100ma(.1a).

All of my machines are rev 8a or rev 6a..  And all three run fine (and have for years) fully loaded with side-car, internal hardisk, and extra ram... and NO ADDITIONAL PSU..

If you have a hard time believeing this, than I dont know what to tell you other than "sucks to be you"...  I sympathise with your past problems, and I suspect that you had earlier and more "power-hogging" designed hardware than is employed in the systems/add-ons that I have..

I guess I could hook my ammeter in-line with the 5v circuit on the PSU of each machine, to see exactly what they are drawing in terms of current, but I really havent the inclination to do so.. Like I said.. It's all worked great for years..
 

[Metalguy66]

I dont think anyone is "mistaken". I just think weve had different experiences..

For example: And A500 rev3/rev5 board has 16 (256kx1)ram chips just to make 512k. This pulls significantly more current than 4 (256kx4) chips on a rev 6a (or later board). You throw in an early model A501 expansion, and guess what.. ANOTHER 16 chips.. Thats 32 ram chips instead of 8 on the later models.

Also, look at the size difference in the stepper motors on the early floppy drives (like the A1010 and early "all metal" mechs used in the first A500s & A1011s) versus the new "plastic" ones used in the later A500s. Floppy drives are consntantly starting & stopping spindles and "grinding away" at the disks moving the head steppers.. Also remember with MFM, it cant start & stop one drive spindle independantly, it does both simulatneously.

Also, look at early hardisk controllers that used all DIP package logic, and tons of it, versus the newer designs that only had one or two small surface mount package custom chips. (eg. the A590 versus the GVP A500 HD+/8)... big difference..

Its also possible that commodore "beefed up" the PSUs in later A500s after so many people b!tched about them burning up in earlier units.

I would expect the A1200/A600 motherboards to be significantly less power-hungry than an A500 due to the fact that almost everything had been replaced with newer, smaller, surface-mount components.

So you see, there's quite a few factors here. I believe him when he says he had problems. Ive heard others say the same thing. Im just glad my particular combinations work with a single stock PSU. Id hate to have YET ANOTHER power cord to deal with, or some "hacked PC unit" looking PSU..

[Metalguy66]

The PSU circuits are on the bottom board. Your gonna have to get a good close-up shot of the bottom board if you want my input..

I would definitely NOT try any more AC voltages unless you know for sure it requires AC... DC voltages will not hurt it even if it's designed for AC, but the opposite is not necessarily true.. You could fry it..

If you can remove those upper boards and get me a good hi-res shot of the lower board (the one the power connector is actually hooked to) I can tell you for sure an appropriate supply voltage for it, as well as the required polarity if necessary.