Myarc cards for sale/repair tips

[RickyDean]

On 4/16/2021 at 11:37 PM, RickyDean said:

O @InsaneMultitasker, I am close to getting my sram project finished, but have a question or two. Then when finished I will continue getting the flash chips operational. In Fabrice's schematics it states " Solder the blue wire from pin #3 of the 74ls138 to the pin #40 of the gate array (AMD signal). But in the 512 doc from Chicago Faire it states "Pin 3 (LS138) to Gate Array pin #42 [Blue]. I have a red wire going to pin 40 not 42, that went to pin 3 (ls138). discrepancy or another way? Also the 1k resistor does it go between 20 and 28 on the 28 pin original sram location? And if you look at some of my prior pics, Geneve backside, the red wire was tied to a 1k resistor at pin 27 along with a white wire. Does that belong there? Thanks for helping.

Bumping this for @InsaneMultitasker

[RickyDean]

Here is my "Nora" daughter board idea for the pfm+flashdisk 74ls139. As you can see in the pics it will plug into the sound socket then the sound chip and 139 will be easily replaced.

[+InsaneMultitasker]

17 hours ago, RickyDean said:

Bumping this for @InsaneMultitasker

Sorry, I'll have to get back to you on the questions later as I'm dealing with a few non-hobby items that are competing for my time...

[RickyDean]

49 minutes ago, InsaneMultitasker said:

Sorry, I'll have to get back to you on the questions later as I'm dealing with a few non-hobby items that are competing for my time...

Understood, take your time. Life is important.

[RickyDean]

On 4/19/2021 at 12:39 PM, InsaneMultitasker said:

Sorry, I'll have to get back to you on the questions later as I'm dealing with a few non-hobby items that are competing for my time...

Also, when you do answer those, I have one more: the pins, 13-15, on the 74ls139, that are soldered to the same pins on the 74ls138, on my pfm+, where should they go if I've moved the '138? Should I run wires to the same pins on the 138, in its new location?

[+InsaneMultitasker]

I encountered a manufacturing/buildout error today.  Do you see the problem ? 

 

[HOME AUTOMATION]

Capacitor installed with wrong polarity?

[+InsaneMultitasker]

53 minutes ago, HOME AUTOMATION said:

Capacitor installed with wrong polarity?

Yep. I couldn't figure out what was bothering me about the card until I put it down and came back to it a little while later.  The capacitor in question is tied into the video circuitry. 

[HOME AUTOMATION]

Mmmhmm, I've found that most of the stubborn issues involve too strong of a focus!

Clearing the mind is often the better part of the solution.

[+Schmitzi]

 

For noobs, which one in the picture is it ?

The big one in the middle?

 

[+mizapf]

I guess so, look out for the light blue strip on it.

[+dhe]

What are the symptoms of putting in that particular capacitor backwards?

[+InsaneMultitasker]

The capacitor (C65) is connected to the Red output line (for the RGB video) and there were no visible (to me) symptoms. It was more a feeling that something was out of place.

[+OLD CS1]

3 hours ago, InsaneMultitasker said:

The capacitor (C65) is connected to the Red output line (for the RGB video) and there were no visible (to me) symptoms. It was more a feeling that something was out of place.

 

Apparently, Amigas suffered the same problem in their audio circuits.

[+InsaneMultitasker]

Found a stray, clipped piece of a lead tacked to the lead of this capacitor when I lifted it from the board.  Had it come loose, it could have rolled under any number of components and nearly did when I tried to fish it out. 

[+InsaneMultitasker]

Wrapping up for the night.  New capacitors installed in preparation for finishing installation of the DC-to-DC converters.  When installing regulators, it is easier to put them into the card first; when installing the converters, it is easier to install the capacitors first.  I want to try some double-sided tape to hold the converters in place because there is no screw-hole and the leads bend quite easily, alas, I had none in my bins. 

 

[+InsaneMultitasker]

Operational. DC-to-DC converters installed.  All but one electrolytic capacitor refreshed or replaced. It almost has that new-Geneve smell!

Tonight I will determine how to approach the V9938 5v reg/capacitor.

[GDMike]

Always Beautiful to see, especially working. Lol

[+InsaneMultitasker]

If I traced the 9938 regulator correctly, there is no capacitor on the output lead.  I don't know if following suit with the DC-to-DC converter will induce noise or other undesirable side effects?  I could probably tie the new capacitors into the circuit at a different location on the board.  Thoughts?

[+InsaneMultitasker]

The V9938, M81, has three .991uF capacitors tied in as follows.  I installed the DC-to-DC converter without adding any additional capacitors to the output side and so far, the system is stable.  I did replace the 22uF electrolytic with a 10uF as recommended for the CUI part. Barring any other considerations or recommendations, I'll consider it sufficient. 

 

 

[+OLD CS1]

So is the DC-to-DC output really clean or are the Geneve's components nice and tolerant?

[+InsaneMultitasker]

After operating for an hour, I checked the temperature of the (now four) dc-to-dc converters.  All registered heat output between 85F and 92F degrees, basically, cool to the touch.  A far cry from the typical 150F to 175F degrees experienced with 7805 regulators.  The card is operating within a standard PEB.

 

1 hour ago, OLD CS1 said:

So is the DC-to-DC output really clean or are the Geneve's components nice and tolerant?

When Richard and I looked at these components a few years ago, they seemed clean "on paper."  Neither of us performed any further analysis.  

 

[+InsaneMultitasker]

Today I finished updating the earlier-pictured Geneve.  Or so I thought. 

 

Back in the Cecure days, we kept a mouse and joystick on the test bench.  Before returning the card to the customer,  we would load up my test programs [some were later cobbled into the CYA program]  to verify operation before shipping the card back to the customer.  Well, that was 25+ years ago. These days I rarely connect a mouse or joystick to my Geneve, since I mostly use it for programming and without a case or PEB cover, the joystick poses quite the liability to the card.  It just so happens that I was playing Barrage a few weeks ago and still had a pair of TI joysticks on the bench.   So I rolled my eyes and begrudgingly connected the joysticks to the Geneve, fired up the OS, ran my old test programs... and was quite surprised to discover that the only functional joystick operation was UP.  Further inspection of the card revealed a cracked resistor network, RN30. 

 

The schematic passively informed me that RN30 is for the mouse but of course, I knew better; the joystick wasn't working and the RN was cracked. The schematic must be wrong.  So, I replaced RN30 thinking, "this was easy" only to find that the joystick still didn't work properly.  Not knowing where my mouse is hiding, I inspected the joystick resistors/resistor network. Everything ohmed out OK.  All that I could think to do was to replace the 9901, which seemed like overkill at the time.  I mean, three directions and the fire button?  That's a lot of 9901 damage! 

 

I replaced the 9901, fired up the test program, and lo-and-behold, the joystick port is now working properly. I re-tested the original 9901 and confirmed the failure.  Good grief.  Now if I can just find my mouse to confirm that replacing the resistor network took care of that problem, I can consider the card 'complete'. (Edit: Mouse located and tested successfully!)   And as an added bonus, I won't need to modify the schematic based on my earlier, faulty assumption. 

 

Quite the reminder to test all operating characteristics of the card while it is on the bench.  Shame on me for allowing my personal card usage (or lack thereof) to cloud my repair judgment.  

[GDMike]

I've got 2 regulators,( edge near LED), that get extremely hot. Much hotter than ram that is nearby, and hotter than the other Regs. I don't know what to do so I put a fan inside the case and left the cover off the Geneve. System runs fine, but I'm not sure about why these 2 are so extremely hot. I did notice that they don't get hot like that immediately, but at an hour they do.

Fan may help it out.

 

[+InsaneMultitasker]

13 minutes ago, GDMike said:

I've got 2 regulators,( edge near LED), that get extremely hot. Much hotter than ram that is nearby, and hotter than the other Regs. I don't know what to do so I put a fan inside the case and left the cover off the Geneve. System runs fine, but I'm not sure about why these 2 are so extremely hot. I did notice that they don't get hot like that immediately, but at an hour they do.

Fan may help it out.

 

Yea, that is 'normal' for the card.  You'll find temps hovering around 140-175F.  The regulators must be installed with heat sinks and thermal compound between the regulator and heat sink.  My development Geneve is operating (cooking)  daily in this configuration, and it has been able to withstand the same for years of 24x7 operation, when sinked properly.  Of course, the card will start turning brown in the vicinity of the regulators and the capacitors will need to be replaced eventually. 

 

Heatwave has been operating for 2-3 years 24x7 using DC to DC converters and an ATX power supply configuration, with 12volts supplied to the converters.  Small sample size aside, the configuration has been quite stable.  I have comparatively little run-time experience with the converters in a standard PEB, though so far they seem stable.