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rebeltaz
January 25th, 2009, 03:58 PM
I don't suppose anyone has a spare read/write head for a Commodore 1541 Disk Drive? Believe it or not, I appear to have an open coil in mine.

Thanks...

Druid6900
January 25th, 2009, 07:31 PM
For the price you can get them for, I don't think a head change would be worth the trouble.

Might as well buy one and use the current one for parts, should it ever need them.

channelmaniac
January 26th, 2009, 12:11 AM
I have a couple of drives in storage that are going to be scrapped out. What model of drive is it? (Teac?)

rebeltaz
January 26th, 2009, 02:18 PM
I have a couple of drives in storage that are going to be scrapped out. What model of drive is it? (Teac?)

It's a Mitsumi D500...


While I'm at it, let me ask this question. I am having the worst luck with these freaking c64s. I have two that have the black screen with no boot up. The third one was working great. I built an XE1541 cable, hooked it up and was running 64HDD on a 1.3GHz system running MS-DOS 6.22. Everything was working great for three or four hours. We were playing Jumpman and the computer froze and the colors started shifting. I turned the c64 off and when I did 64HDD exited - it normally restarts 64HDD when you turn the c64 off and back on. Anyway, I turned the c64 back on and lo and behold - freaking black screen with no boot.

Is there anyway that the XE1541 cable I built - that was working fine for several hours - screwed up the c64?

I am about aggravated. I'd still like to fix the real 1541, though to use with the VIC-20 - which I have no intention of hooking up to the 64HDD yet!

carlsson
January 26th, 2009, 03:15 PM
A very long shot, but perhaps you suffered from different ground potentials on the PC and the C64? E.g. they were connected to two different wall outlets. I've read that strange things may happen then, but perhaps it is exaggerated.

I have one of my two 1541-II's connected to the PC via an XM cable, and due to I'm short of power supplies I also power it from the PC, 5+12V. I imagine it won't cause any difference in potentials since the drive is powered from the same supply as the PC is.

rebeltaz
January 27th, 2009, 02:56 PM
A very long shot, but perhaps you suffered from different ground potentials on the PC and the C64? E.g. they were connected to two different wall outlets. I've read that strange things may happen then, but perhaps it is exaggerated.

I have one of my two 1541-II's connected to the PC via an XM cable, and due to I'm short of power supplies I also power it from the PC, 5+12V. I imagine it won't cause any difference in potentials since the drive is powered from the same supply as the PC is.

Well, the two were on different sockets, but I would have thought that a ground fault problem would have shown up relatively quickly and not after several hours of flawlessy operation... I may be wrong and if I am, let me know... I'm scared to try the XE1541 again - I'm running out of c64s!

channelmaniac
January 27th, 2009, 05:28 PM
Well,

If the vents are blocked then the PLA will overheat & die. That chip should have a heatsink on it but Commodore in their infinite cheapness left it off.

Also, if you have a bad power supply you'll run through 64's like crazy.

RJ

docred
January 27th, 2009, 07:21 PM
The different ground potential issue I've seen before with audio equipment, where it can be discovered somewhat quickly when you start soundchecking mics, amps, PA systems, etc. I've head of it with computer equipment, I'm sure I've read something referring to it before. Sometimes a person has bad grounding in their sockets and doesn't know it right away. I'm not sure, but I suppose some stray potential voltage leaking from a psu might take a bit of time before it damaged some circuits.
In a similar vein, some of the C64/vic psus were notoriously cheap and flaky. Might be worth testing it to see what its putting out.

rebeltaz
January 27th, 2009, 08:07 PM
Well,

Also, if you have a bad power supply you'll run through 64's like crazy.

RJ


When you say bad, you mean as in how? No 9vac or 5vdc? Low or high voltages? Intermittent? I've measured all of the supplies and I am getting 5vdc and about 11vac unloaded on all of them.

If the supply(s) were bad, what would they damage, if anything in particular?

channelmaniac
January 27th, 2009, 09:17 PM
They would most likely damage RAM.

The epoxied bricks were notorious for cooking themselves and not regulating their output properly.

I use an aftermarket power supply made specifically for the C64 on my testbed machines.

RJ

rebeltaz
January 27th, 2009, 09:47 PM
They would most likely damage RAM.

The epoxied bricks were notorious for cooking themselves and not regulating their output properly.

I use an aftermarket power supply made specifically for the C64 on my testbed machines.

RJ

Other than frying c64s, how do you test the supplies? I assume you're talking about the 5v line. Like I said they all measured 5v, but that was unloaded. And if the supply gets more unregulated as it heats up, that could explain why the one i was using ran for several hours before biting the big one.

I guess I could load the supply and keep a constant eye on the voltage, but I'm sure that this problem has already been tackled and I'd just as soon not re-invent the wheel!

Thank you.....

wiskow
January 28th, 2009, 01:18 AM
The "black brick" C64 power supply has no safety features built into it other than a fuse and so, when the voltage regulator dies, usually because the filtering capacitor is no longer doing its job properly, the regulator will go into shorted or continuous conduction mode. When that happens, up to 8V (with a huge ripple) can come out where you would normally expect 5Vdc and this usally destroys the DRAM chip of the 64 it powers.

Also, the black brick is very difficult to repair because it is filled with epoxy.

The only Commodore-made power supply that's really good for 8-bit computers is the Commodore 128 power supply. Some people convert these into a C64 power supply by attaching an adapter or cutting the cord and replacing it with a C64 7pin DIN connector.

rebeltaz
January 29th, 2009, 09:44 AM
OK... well going on your responses, I decided to test the power supply that I had been using. The supply says that it's output is 5vdc at 7.5w (1.5 amps). Using that, I loaded the supply with a 1.2 amp load and constantly measured the current and voltage output. First thing I noticed was that instead of a rock solid 5v, from the outset I had 4.8v. I left the supply running continuously for two hours and as time went on, the voltage slowly dropped down to 4.6v. Then at about two hours, the voltage suddenly dropped to 2.1v.

So I guess it is the supply causing my problems :(

My question is, with low voltage, what is the possible damage?

Thanks, again...

channelmaniac
January 29th, 2009, 11:16 AM
Hard to say.

When I see a black screen failure I check the PLA first. It's the most common chip to fail and is almost always socketed.