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InsaneMultitasker

Myarc cards for sale/repair tips

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That one is on the same level of sneaky as a disk controller Arcade shopper sent me to look at last year. Two little whiskers of solder where they didn't belong (shorting some of the pins under the DSR chips). That was a careful hunt, as they are waaaay too easy to miss on a visual check. Nice hunting there, o Insane One! 

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15 hours ago, InsaneMultitasker said:

Operating under the assumption that the gate array pin tied to SNDRDY is a gate array output (which may be false and needs to be confirmed) I got to thinking about the removed buffer chips and 'coincidence'.  You posed the following 'question':

GA 32 ready* goes to Pbox 4 ready* with a pullup. I wonder if this is an input or output for the GA. My guess is an input from other Pbox cards.

 

Thinking along these lines I looked at how Pbox 4 is tied into RN54.  I ohmed out RN54 - all pullups checked out.  I then tested for continuity between +5 and each pin of RN54; all normal.  I then checked continuity between GROUND and each pin of RN54 and found a problem.  Pin #2 was shorted to ground.  This is the pullup for the external peb -HOLD line.

 

Working from RN54 pin #2 I followed the trace under a capacitor I had replaced; no issue there.  The trace flipped to the back side of the board where it meandered past a few chips among them one of the buffer chips I removed.  The  trace is missing some solder mask (like many other traces on this board) where it curves around the buffer chips GROUND through-hole. I found a very thin strand of solder bridging the HOLD trace to ground. I removed the solder bridge and confirmed HOLD was no longer grounded.  I placed the card into my PEB with PAL pin 3 in place and the Geneve displayed the swan.  

 

When I first started working on the Geneve I noticed that flexing the card slightly could stop the card from booting. It is possible this strand of solder was making intermittent contact, forcing HOLD low and halting the Geneve from booting. 

 

Thank you, FarmerPotato, for digging further into the PAL and steering me in the right direction.  I truly hope that after the sockets are installed the Geneve will work as expected, with no odd behavior or periodic lockups. 

 

 

 

 

This is some awesome detective work, IM!

Thank you for running this wily fox all the way to ground (heh heh).

I'm still digesting your questions and how to answer specifically.

 

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13 hours ago, Ksarul said:

That one is on the same level of sneaky as a disk controller Arcade shopper sent me to look at last year. Two little whiskers of solder where they didn't belong (shorting some of the pins under the DSR chips). That was a careful hunt, as they are waaaay too easy to miss on a visual check. Nice hunting there, o Insane One! 

Yes, this one was very sneaky. Were it not for the PAL issue pointing the way, I don't know if I would ever have found the short with any visual inspection.  It looked like just another section of trace missing its solder mask.  I am reminded of the days I spent hunched over a batch of bad HFDCs looking for shorted traces... ah, those were the days.  :ponder:

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Does anyone here have recommendations for what to use to clean old circuit boards?  I'm having trouble removing old flux and residue.  I suspect some of the residue left behind during the desolder process is organic core; I primarily use rosin.  I  typically use isopropyl alcohol and a soft toothbrush for minor cleanup, yet there is some stickiness left behind. 

 

I no longer remember what we used at Cecure for cleanup.  We often left the rosin flux behind.  I don't want to use a cleaner that requires stiff mechanical action i.e., bristle or hard brush, as many of the boards cannot survive a scrubbing and would suffer removal of trace mask in the process.   Thoughts?

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9 hours ago, InsaneMultitasker said:

Does anyone here have recommendations for what to use to clean old circuit boards?  I'm having trouble removing old flux and residue.  I suspect some of the residue left behind during the desolder process is organic core; I primarily use rosin.  I  typically use isopropyl alcohol and a soft toothbrush for minor cleanup, yet there is some stickiness left behind. 

 

I no longer remember what we used at Cecure for cleanup.  We often left the rosin flux behind.  I don't want to use a cleaner that requires stiff mechanical action i.e., bristle or hard brush, as many of the boards cannot survive a scrubbing and would suffer removal of trace mask in the process.   Thoughts?

I want to know too. I’ve tried 99% isopropyl (after 70%). Internet says you have to flush the solution off (in my case, it just moves the gunk around.) I’ve tried repeated squirting with eyedropper. 

 

internet also says use ethanol.

 

i haven’t tried submerging.   

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Here's a liquid type as well, that is somewhat less aggressive, but still expensive. I also found some of the more aggressive stuff in an an applicator pen that would limit waste when compared to the aerosol initially identified.

Edited by Ksarul
Added data.

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I've submerged empty boards and boards populated with passive components. I don't think I'd feel comfortable submerging a populated Geneve, though.  White, hazy  residue seems to be the toughest thing to remove from the old populated boards.

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On 8/3/2019 at 11:58 AM, InsaneMultitasker said:

I've submerged empty boards and boards populated with passive components. I don't think I'd feel comfortable submerging a populated Geneve, though.  White, hazy  residue seems to be the toughest thing to remove from the old populated boards.

I do, often after cleaning with 91% alcohol, take and wash my boards with warm soapy water and use a tooth brush to clean the areas affected. Then I run warm water over them while brushing to remove the soap, works pretty well. Then I take, and either place the board in front of a fan for a good while, or leave the board in the hot Georgia sun for a length of time, checking it fro moisture ever now and again til I'm convinced it is dry all over. Then I let it alone in the house for the night and have no issues, and have done this for many years. Maybe not the best practice but it does the job.

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On 7/29/2019 at 8:38 PM, InsaneMultitasker said:

  I truly hope that after the sockets are installed the Geneve will work as expected, with no odd behavior or periodic lockups. 

 

Worked ended early (hah) and it was "only" 84F in the garage as of 11pm.  Figured I would unwind by installing sockets so that I could fire the Geneve up. I am happy to report that it loaded MDOS the first time through. I don't know that I want to induce the Geneve to fail -- I'm hoping that replacing the bad sockets, fixing the crystal solder joints, and removing the sneaky solder tail will suffice.  This card and I are destined to part ways soon ;)

 

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during my testing last weekend it seemed that when I inserted the clock/sound chips into their sockets, the Geneve would exhibit some strange symptoms.  Further inspection showed some moderate corrosion near the top of the socket leads, so I decided to inspect the area more closely.  While preparing to remove the sockets I happened to notice the clock chip crystal was very, very close to a lead from the adjacent capacitor.  The lead was bent inward.  When I checked continuity between the two, it only required the tiniest nudge of the crystal to short to the lead.  With just a bit more luck, I'm hoping this is the end of the proverbial tunnel. 

 

 

clock capacitor touching-Geneve.PNG

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While putting the Geneve through a few hours of testing, I gnawed on the final card on my bench - an HFDC that was fried by over-voltage a few years ago that I had repaired to the point where it would do everything except format a hard drive. 

 

A few chips in the hard drive circuitry had not yet been replaced as they are common to both the floppy and hard drive logic, nor could I see any reason a format would fail when all reading/writing worked.  So I bit the bullet to replace the common chips to rule out some weird situation where the floppy worked but hard drive did not.

 

In the older HFDC card revisions, Myarc had forgotten to add a spot on the board for the capacitor tied to the 'step' line, so the cap is mounted to the back of the card.   (This was fixed on the last board run, along with the capacitor placement for the 9223 and a few other changes).  I noted the capacitor pin connection points but forgot to take a picture, so I went back to the schematic to confirm/compare my work notes.  It seemed the capacitor had been connected to the wrong pins long ago. I had to flip the card front-to-back at least 5 times to make sure I was looking at the right pin numbers (it can get confusing!).

 

Turns out the capacitor was tied to the 'step' output when it should have been tied to the input.  I suppose this was holding the output high too long and/or beyond the point the input was supposed to be active?  Without a scope, I can't confirm this conjecture; what I can confirm is that the HFDC formatted a hard drive for the first time in 3+ years.  :)  

 

If I've learned anything this year it is to keep an eye open for misplaced or improperly connected/mounted passive components, wrong resistor values, etc.   With luck, I can run this card through its paces today and return it to its owner soon.  Then I will turn my attention to refreshing some of my own equipment before I dig into the MDOS 7.00 problem.

 

 

formatting hfdc.PNG

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