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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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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.


Another Georgia guy! Yep, it’s been a scorcher of a summer.
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15 hours ago, acadiel said:

 


Another Georgia guy! Yep, it’s been a scorcher of a summer.

 

Yes it has, and my central air went out two months ago at the start(bad compressor, in the process of replacing soon) and we have had to get by on two window a/c's in the bedrooms and fans everywhere else. I get my TI/Myarc repairs worked on after I deal with these issues(trying to keep this on topic).😢

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Ricky, I got three components coming in for that Ramdisk this week. A 259,154 and a 74LS02. I've removed all those 32k chips and replaced with 8Ks. I pulled off all jumpers and now im assuming I can follow the instructions of assembly. I wanted to let you know..I better get outta here with my ramdisk now before they kick me out! Lol

IMG_20190817_142658280.jpg

IMG_20190817_142557023.jpg

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24 minutes ago, GDMike said:

Ricky, I got three components coming in for that Ramdisk this week. A 259,154 and a 74LS02. I've removed all those 32k chips and replaced with 8Ks. I pulled off all jumpers and now im assuming I can follow the instructions of assembly. I wanted to let you know..I better get outta here with my ramdisk now before they kick me out! Lol

 

 

It looks great so far, you've got this. Good practice for those 4000B cards. 😄

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I did a v check on the hrd+ I have..I guess it's not adequate to run these 3 stacked 138s and 2 stacked 259s and 2 stacked 154s along with the ram?? Im pulling 4.75 or so on my 7805 and a lot is being pulled before hitting the stacks as my meter says. I'll just wait for the new ramdisk!! 

IMG_20190823_091459.jpg

IMG_20190823_101347771.jpg

IMG_20190823_091317739.jpg

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On 4/27/2019 at 5:18 PM, InsaneMultitasker said:

I just finished replacing the linear regulators on a 2nd Geneve so that I can eventually send the Heatwave card back to its owner, now that it's had a 6+ month burn-in. The newly updated Geneve and FDC are in the same PEB playing nicely together. I'll hunt down my DM2 cartridge dump so I can run both cards run for a while.

I found my Kill-a-watt this morning and measured the PEB-based difference between a standard Geneve with linear regulators and a Geneve with the three 'hottest' regulators replaced by switching regulators.  My empty stock PEB draws 34 watts. The standard Geneve increases the total watts by 21-22.  The updated geneve only increases total watts by 12-13.   I have not yet replaced the V9938 regulator so I expect total power draw to drop a bit whenever I get around to it.  I'll perform a similar test with my tower/pc power supply when time permits.

 

 

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This weekend I opened up one of the cards I promised to repair before announcing that I needed a break.    The card appears dead; unable to read the EPROM via minimemory, no apparent CRU activity.  Being an older revision card it still had the QIC02 circuit, the old Motorola LS31/LS32 transceivers, and the original voltage regulators.  The regulators were outputting 5.4 volts, something I have not seen on the HFDC in the past. Nominal output is 4.99 to 5.03.  

 

When I refresh an HFDC I start with cleanup which typically includes:

1. Remove the QIC02 chips and socket (U22, U23, U24, and U26) and adding a jumper to the back of the card. (I'll have to identify the source pins; I just know the location by sight after all these years).

2. Replace the 5v regulators and add thermal compound; add heat sinks if not already present

3. Replace the electrolytic capacitors.  Fortunately, there are only 5.  I typically install the front 5v regulator capacitor horizontally (by bending the leads) to reduce chances of someone twisting the screw, forcing the heat sink into the capacitor leads, and ultimately shorting the cap.  (Seen it a few times in 20 years). 

4. Socket the two LS245s. These tend to take damage over time.

5. Socket and replace the LS31/LS32, especially if they are the original Motorola chips.  When flakey or bad, the MFM hard drive will present errors during the format stage and/or won't complete a format.  Replacement of the chips usually clears up the errors.  

6. Optional: The 12v regulator doesn't go bad that often so if it is working well, I usually leave it in place though I check for thermal compound and apply some if needed.

7. Cut a 'key' into J2 for the hard drive connector with a thin hacksaw blade, taking care not to damage the front fingers (the back fingers are all ground)

8. Replace LED if the old one is dim or not working

9. Assess RAM, EPROM, 9223, and 9226 sockets for possible replacement if damaged or 'worn out'.  Some of the sockets are single wipe and prone to poor connections with the chip.

 

A continuity check on U35 indicated one open connection; removing the socket I discovered that an earlier replacement had rendered the trace detached from the through-hold and the pad connection missing.  This doesn't fully explain the EPROM situation. 

 

image.png.5e490688510c2e9651216d8b0e4cc9ce.png
 

Picture of cleanup in progress with some of my test chips in place.  I removed U31 since the card's symptoms indicate possible problem with that chip as well.

BE647732-5A6E-4ECC-B9F7-12349C4AEF21.thumb.jpeg.dae72813b518e48749f1a5efaa5405ca.jpeg

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While prepping through holes I caught glimpse of what looked like a hairline crack in the diode directly below U37.  When I unsoldered one of its leads the diode 'fell apart' i.e., it had cracked in half.  This diode is connected to RDBENA.  With a new diode in place, the LS245 data line repaired, and all chips in place I checked continuity and ohms across the capacitors and regulators.  Finding no shorts and resistance at expected levels, I performed a successful smoke test.  The card powered up and the EPROM was readable.  I then connected my test MFM drive and successfully loaded MDM5.  Both the floppy and hard drive catalog successfully.  I still need to put the card through its paces and check it after a few hours of operation.  

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