Need help/suggestions on a dead C4P-MF

Andis
Posts: 33
Joined: Sat May 13, 2017 8:15 pm
Location: Rocky Mountains, USA

Need help/suggestions on a dead C4P-MF

Post by Andis » Tue May 30, 2017 1:08 am

Hi All,

First thread I have started here, but have lurked quite a bit and responded to a few posts. I find this forum great, quite useful, and FRIENDLY!

I'll try and keep this post as short as possible (hard in this case since I don't have a very specific question). I have a basically stock C4P-MF as described in my signature. I say basically since it started out as a cassette based system but was factory modified to add one 5" mini-floppy. Note, I'd really like to keep it as original as possible.

I pulled the system out of storage after 35 years of storage from it's original, fitted foam packaging/box. I spent a few good solid days (over a few weeks), re-seating some cables, chips, etc and finding a monitor that would display the signal (turns out my 51" plasma TV worked best of all things), and investigating if ASM, EM and the 9-bit Basic utilities worked. The only problem I noticed was that I clearly had an overheating issue. When I spent more than somewhere between 15 and 25 mins running and/or coding things, the computer would become unresponsive, but not shut down. I did check to see if a hard reset immediately after the hang would reboot successfully, which it did. However, using this approach, the computer was too hot to reliably run programs (i.e. I would get BASIC errors, which did not appear if I let the computer cool properly for 30 mins or so). From this point on I carefully monitored how hot the computer was getting. In retrospect, I should have at this point started to investigate the overheating issue while I could still measure voltages, etc.

What finally happened was that after coding a routine to test the audio, and running it successfully, I forgot abut the thermal time factor. I was so over joyed at having everything working as expected, and it looked great, and I WAS FINALLY DONE! I was just sitting there admiring it, clarity of the text, etc. So, I wasn't typing anything, or running anything that would have shown my non-responsive " thermal hung up state". To my horror, it just shut down while I was taking a few photos. I'm not sure if I remember properly, but it didn't sound like a normal shutdown. Just seemed to go dead quiet. I am assuming it is a power supply issue, but this is where my lack of knowledge comes in, If I put in a new fuse, it just blows it out in about 1/2 sec, at the point that it seems the machine is just getting ready to start boot-up.

So, I can't power it up to put a voltage meter in there. I am thinking of various approaches, but this is where I could use the forum members help and critique.

1) Can I just disconnect the power supplies (I have 2, believe one is dedicated to the 527 memory expansion board) from all the circuitry it powers, jump the fuse, and check the output?
2) I could just remove the one power supply from the circuit that powers the 527 memory expansion board (and remove the board) and see if I luck out and have only one bad power supply?
3) Order and put in a new power supply, at least for testing purposes (I'd like to keep it "stock" as I said previously)? If this is a good approach, what type of power supply do I need> Specs, etc?
4) Am I already thinking down the wrong path!?! Could I have blown a chip or something? I pulled all the boards and checked them and the cables for obvious electrical/thermal damage and saw none.

Finally, which I hope is a minor issue, when pulling the boards (which I've done numerous times), I snapped off a pin from one of the 16 pin blue connectors. D'OE, what an idiot. I'm hoping I can scrounge up a new one of those, or a complete 16 pin ribbon cable? Is this part hard to get?

Anyways, thanks for reading this far. I'm kicking myself for not just shutting her down and going on to investigate the thermal issue later. Any and all comments and suggestions welcome and appreciated.
C4P-MF, 540 RevB-1/542, 527 w/12K, 527-RevA w/24K, 505-RevB

Klyball
Posts: 195
Joined: Tue Dec 09, 2014 12:53 am

Re: Need help/suggestions on a dead C4P-MF

Post by Klyball » Wed May 31, 2017 1:01 am

Hi and welcome

I m gonna guess a bad cap after all this time

A couple of photos of the supplies would be great

Disconnect the 2 supplies from the system and check the voltages and if you have a scope check for excessive ripple DON'T JUMPER THE FUSE these old liner supplies are usually easy to fix and you can keep it original if the supplies check pop out all the boards and check the resistance across the power rails with the supplies still disconnected if you get a short reading it's on that board

If there are any tantulum capacitors this would be the prime suspect ,also the big filter caps could need to be replaced

If the fuse still blows when disconnected from the system
It a bad supply and we can go from there

Cheers
Replica 600 Rev D:8K,CEGMON
Replica 610 Rev B: 24k,MPI B-51 with Custom Data separator D-13
510 on the bench/replica 582 backplane/replica 470a /replica 555/original 570B/2 x Shugart 851
Ongoing : 630 ,620 ,510,542c,custom 590,SA1200,592,594,596,598

MK14HAK
Posts: 350
Joined: Wed Mar 16, 2011 1:49 am
Location: New Zealand

Re: Need help/suggestions on a dead C4P-MF

Post by MK14HAK » Wed May 31, 2017 3:00 am

how to delete double post ?
Last edited by MK14HAK on Wed May 31, 2017 9:07 pm, edited 1 time in total.
600RevB:16K,2MHz,64x32,470,CEGMON
SuperKit:502,540B,542B,CEGMON, 8" and 5" FDDs
Cards:PE IO,6522 D-A-D, AY3-8910,ProgramGraphics,Color,UK101
WIP:HexDOS,FDD Emulator

MK14HAK
Posts: 350
Joined: Wed Mar 16, 2011 1:49 am
Location: New Zealand

Re: Need help/suggestions on a dead C4P-MF

Post by MK14HAK » Wed May 31, 2017 3:12 am

While you have your system in pieces it's a good time to clean those problematic 48P connectors. Dave gave me a good tip in using the DeoxIT products followed by some conductive gel (I can't remember the name of) and my rig has been far more reliable since the cleanup. In my case I concluded the socket side is more the culprit but its also the harder to clean.
Also its handy to record the current consumption of each board as you put your working system back together.

'A couple of photos of the supplies would be great'
Agreed.
It would be great to have a collection of exposed SYSTEM photos on OSIWeb. Some nice close ups as per glitch's C3 etc. C2 C3 C4 C8 Backplanes, PSUs, I/O connectors. I know there are some in places on the forum but finding them can be a mission. We have most of the boards covered already, how about some pics of your system next time you pop the lid folks ?

Mike
600RevB:16K,2MHz,64x32,470,CEGMON
SuperKit:502,540B,542B,CEGMON, 8" and 5" FDDs
Cards:PE IO,6522 D-A-D, AY3-8910,ProgramGraphics,Color,UK101
WIP:HexDOS,FDD Emulator

Andis
Posts: 33
Joined: Sat May 13, 2017 8:15 pm
Location: Rocky Mountains, USA

Re: Need help/suggestions on a dead C4P-MF

Post by Andis » Wed May 31, 2017 3:55 pm

Hey guys, thanks for the responses. It will take me a period of time to do everything suggested, a few hours a week I'm guessing. I did reset one 48 pin connector (didn't clean) and that seemed to be a major help in getting it going... I don't have a scope and over the years I've even lost my soldering iron, but I'll get back into it. I do have a voltmeter/multimeter...

Just a few photos to get started... will take more as I proceed.. and check in once or twice a week.

The overview of the power side...
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top side of what i assume are big capacitors, 527 mem one to the the right. Didn't notice until i took these closeup photos but the 527 cap seems to look much better, if that's any indication
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Closeup up of one of the main capacitors
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Closeup of the 527 mem , not sure, transformer? I don't have any schematics for the power side at all and couldn't find any...
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Closeup of the main transformer? This also looks worse than the 527 mem transformer
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and finally, just the backside of the power switch and fuse wiring. The black wire going out of the top of the whole is a ground that was attached to the bottom of my floppy disk (back in those days, my house didn't have 3 prong plugs and I had a 30 ft ground going to a cold water pipe also). To the right of that is the back of the power switch. Interestingly, it appears the fan runs on 120V from following the wires.
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i'll check back later. I REALLY APPRECIATE ALL THE RESPONSES. Thanks...
Last edited by Andis on Thu Jun 01, 2017 1:38 am, edited 1 time in total.
C4P-MF, 540 RevB-1/542, 527 w/12K, 527-RevA w/24K, 505-RevB

Andis
Posts: 33
Joined: Sat May 13, 2017 8:15 pm
Location: Rocky Mountains, USA

Re: Need help/suggestions on a dead C4P-MF

Post by Andis » Thu Jun 01, 2017 1:30 am

Hi Mike,

Sure I'll be happy to post some photos as I disassemble. I getting the feeling that I'm going to have to at least disable part of the 1 PSU (the main one) and then can get a shot of the circuit board behind the large caps. I also am curious about the board attached to the inside back of the computer, i can't see a model stamp on it, at least right now. All my I/Os aren't hooked up, but I'll get a good shot of them anyways. I'll probably start pulling the boards tomorrow (the PC is already upside down and I have the board spacers, screws pulled). I assume you have enough photos of the cable and molex connections. But i will do a good job on the backplane, I seem to remember that the 527 24 K expansion slot had an extra power rail vs the other slots, probably to isolate it to it's own power supply.

As to deleting a double post I don't have a clue. Edit it and delete everything?

Finally, since this project feels like it will take a while, is there a source for the 16 pin connectors (blue ones on mine, like below)? I broke a pin on one of them. I could order it now or is it a repair Job? I calculated the cable has somethng like a 1.17 mm pitch and I only see 1.0 and 1.25 mm pitches being sold now for connectors/headers.
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C4P-MF, 540 RevB-1/542, 527 w/12K, 527-RevA w/24K, 505-RevB

gekaufman
Posts: 38
Joined: Mon Nov 23, 2015 12:57 pm

Re: Need help/suggestions on a dead C4P-MF

Post by gekaufman » Thu Jun 01, 2017 3:16 pm

Filter caps on the left power supply look like they are history. I'd replace all electrolytics in the power supplies while you are working on them, then re calibrate the potentiometer for 5v. I'd be suspicious that that is the reason for your fuse issue.

The 16 pin connector is a standard dip header. It is available thru most standard electronic suppliers including Mouser and Digikey.

dave
Site Admin
Posts: 561
Joined: Tue Sep 09, 2008 5:24 am

Re: Need help/suggestions on a dead C4P-MF

Post by dave » Thu Jun 01, 2017 6:29 pm

I second everything in the above post. Here are links for replacement connectors at JDR and Mouser. You can just cut off the bad connector and press the new connector on the end.

I agree with the above post about the caps--they look like they've had it. As already suggested, replace all caps, and check the voltages with all the boards removed. The LM723 regulators have been known to fail as well, so if the voltage is way off with the caps replace and no visibly burned parts, that's what I'd look at next.

Good luck and keep us updated with your progress.

Dave

Andis
Posts: 33
Joined: Sat May 13, 2017 8:15 pm
Location: Rocky Mountains, USA

Re: Need help/suggestions on a dead C4P-MF

Post by Andis » Thu Jun 01, 2017 7:57 pm

Thank you both. I have been trying to find these parts on my own (mostly mouser and digikey) but i guess i don't know the terminology well enough. I spent 2 or 3 hours looking for that "DIP Header", another 3 hours looking for the capacitors (still looking on the caps). Thanks gekaufman for that "dip header" phrase, once i knew what i was searching for, i could find it on digikey. And Dave, thanks for the mouser link to confirm what I found on digikey was correct (digikey has a blue colored one so i'm going with that). One major problem was I was filtering on the CABLE pitch, not the PIN pitch. D'oe.

I did read in an old post on the forum that the LM723CN regulators tend to go, so i am going to order 2 from digikey (made by Texas Instruments, but it looks compatible).

Now I am stuck with lack of knowledge on the caps... Aside from being 10000uf and 16VDC (and at least tolerate 85C temps) , Are they Aluminum Electrolytic Capacitors ? Also, I can't find anymore that are configured the way the old ones are, that is, more like a D cell battery with + on one end and - on the other. I've filtered on axial, radial, snap-in and more. I don't expect to find an exact replacement, but i can't seem to find anything that at least would look "old style". If I have to, It looks like I could just get a Snap-In and run some extra wiring while soldering. Any Capacitor Replacement suggestions Dave, or anyone else of course?

I do plan on pulling all the boards and checking the resistance across the power rail, etc like Mike suggested.

I'll also pull off the caps on the bad PSU today and get a photo of the circuit board behind it and post that as the start of my photo project for mike.

Finally, I know I would really like to keep it "stock", but I'm somewhat considering just buying a new PSU like Jeff did in this old post (bottom of page 1): http://www.osiweb.org/osiweb/osiforum/v ... v+10a#p622. It's really tempting just to be able to snip some wires, add some lugs, and screw it down :lol:
C4P-MF, 540 RevB-1/542, 527 w/12K, 527-RevA w/24K, 505-RevB

Andis
Posts: 33
Joined: Sat May 13, 2017 8:15 pm
Location: Rocky Mountains, USA

Re: Need help/suggestions on a dead C4P-MF

Post by Andis » Fri Jun 02, 2017 12:03 am

As promised, starting on a few shots of the system boards and I/O.

Shot of the video/audio/DAC/cassette (unused) hookups, the Color Adjustment, and the Fan. I will edit this text later to clarify what is what later. Does anybody want me to unbundle the wires going from the hookups to the Molex connecters and take another photo for clarity?
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Shot of IO Board, serial ports, etc. Ditto on editing text to clarify later. Computer is upside down (applies to all photos shown in this post)
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Outside shot of the ports corresponding to the C4P IO Circuit Board shown above. NOTE: the photo has been mirrored (see placard text) so that this photo can easily be compared to the above circuit board photo.
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C4P-MF BackPlane (board 582)
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C4P-MF Backplane.jpg
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UPDATED PHOTO. Much better shot that shows the hookup of the Backplane power rails to the PSUs. Just a bit of the 527 mem PSU is visible at bottom of the photo. Note the 2 black wires coming off the power switch on the back of the computer that run near the bottom of the IO Board to the fan.
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I'll get to the PSU circuit board shots later. Just don't want to snip off the Caps until I know for sure that I'm trying to stay "stock". If I decide to go with a new mini PSU, I'll leave the PSUs as they are (for now).
C4P-MF, 540 RevB-1/542, 527 w/12K, 527-RevA w/24K, 505-RevB

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