Myarc cards for sale/repair tips

[+InsaneMultitasker]

10 hours ago, AwkwardPotato said:

It's a symbol found on many bottom-of-the-barrel phony TI parts. Seems that they only bother engraving one half of the TX...

@Ksarul said something similar to me about this looking like a partial or deformed TI logo.  The chip initially "worked" and then failed miserably.  I now wonder if the failure coincided with my HFDC gate array going bad, and if the chip somehow caused that damage.  Doubtful, but it makes me pause and think...

 

I found this article interesting as I have used the named suppliers in the past and one of them is where the bad chip came from

 

https://northcoastsynthesis.com/news/beware-fake-parts/

 

 

[+InsaneMultitasker]

Ok, no more tears!!!   The Genmod system is on its way to its owner as of this afternoon.  And for the first time in a long time, my bench is clear of all pending repairs, and my room is again recognizable!   I might have to celebrate by tearing down my development Geneve to refresh the capacitors and install (test) a few DC-to-DC converters on the HFDC and SCSI cards.   Woohoo! 

[mvancopp]

On 5/31/2022 at 7:07 PM, InsaneMultitasker said:

Ok, no more tears!!!   The Genmod system is on its way to its owner as of this afternoon.  And for the first time in a long time, my bench is clear of all pending repairs, and my room is again recognizable!   I might have to celebrate by tearing down my development Geneve to refresh the capacitors and install (test) a few DC-to-DC converters on the HFDC and SCSI cards.   Woohoo! 

I have used 8 of these buck converters:

10PCS DC-DC 12-24V To 5V 3A Step Down Power Supply Module Voltage Buck Converter | eBay

 

10 pcs = $10.95 + $1 for shipping.

 

Example: I have replaced the 7805 TI PEB side) on the Myarc 512 card with one of these. It runs very cool, almost no heat. I also removed the externally supplied 7805 and "OR'ed" the external and PEBox supplies using the card's existing diodes that are in-line with the power traces. This allows the single buck regulator to work with either supply (I used a regulated 9 volt 1 amp supply and the PEBox supplies about 11.5 volts). When the two 7805s were used the external 7805 got very hot. This is a simpler, more cost effective, and prevents the two regulators from "fighting" each other. 

The buck converters above are adjustable (variable) but also have a fixed mode for 3.3, 5, 9, and 12v.  believe they adjust up to 24v and supply up to 3A. They default is variable. To use the fixed mode you must cut the small trace connecting the variable option and use a solder bridge or a jump to select the fixed option. I put header pins on them and can drop them in place of the 7805s. I have also used these to power my HDs for the HFDC. They work great, again with virtually no heat and they are far more efficient then the power/heat waste of the 7805s.

 

I hope this helps and may save you some time.

 

Mark

 

[+InsaneMultitasker]

26 minutes ago, mvancopp said:

I have used 8 of these buck converters:

10PCS DC-DC 12-24V To 5V 3A Step Down Power Supply Module Voltage Buck Converter | eBay

Thanks, Mark. I will check this out!

 

See the below link for the part that was recommended to me years ago - I've used it in a few cards, including the Heatwave BBS's Geneve that has been running 24x7 for nearly four years. Heat is negligible, running in the 80-90F range last time I checked.   They are however more expensive.  

 

What sort of hard drive (HD) are you powering and how did you set that up?  Did you use both 12v and 5v converters?  Would be neat to see a few pictures, too   

 

https://www.cui.com/product/dc-dc-converters/non-isolated/v78-1500r-series

[mvancopp]

20 hours ago, InsaneMultitasker said:

Thanks, Mark. I will check this out!

 

See the below link for the part that was recommended to me years ago - I've used it in a few cards, including the Heatwave BBS's Geneve that has been running 24x7 for nearly four years. Heat is negligible, running in the 80-90F range last time I checked.   They are however more expensive.  

 

What sort of hard drive (HD) are you powering and how did you set that up?  Did you use both 12v and 5v converters?  Would be neat to see a few pictures, too   

 

https://www.cui.com/product/dc-dc-converters/non-isolated/v78-1500r-series

I believe I looked at the CUI regulators but I did not have any reliability history or recommendations, they lacked the ability to change the voltage, and the cost seemed out of line. So when I found some inexpensive regulators that could handle 3A, were "pin compatible" to the TO-220 78XX, had a wide input voltage tolerance, and could fulfill multiple voltage needs, I decided it was worth a try. Although they have worked very well I only have a few months of continuous operational experience, no long term reliability knowledge yet. 

I power ST-225 HD drives with them and a few cards (I haven't done the Geneve yet). I did power both 12v and 5v using them for the HD, but decided to use a wall 12v PS and only regulate the 5v. It powers both the ST-225 and a GoTek in the same floppy enclosure, an old TRS-80 drive enclosure. The 12v also ran only a little warmer than ambient under normal use, which should have been 1.25A - 1.5A. 

I do not have any pics but the next time I am in those machines I take some.

 

Mark

 

[+InsaneMultitasker]

The chip distributor refunded me for the LS02 and LS00 chips with an apology for "the mistake". There was no admission that the parts were counterfeit nor was any other reason given.  I will be wary of purchasing from them in the future, and wonder if I need to consider any other chips suspect, even though they have what look like proper labels that match what was advertised in the parts info. 

 

[+Ksarul]

I usually use Unicorn, Mouser, or Digi-Key for parts orders, as they all generally buy their stocks from the OEM. That generally minimizes the chance for bad parts.

[+InsaneMultitasker]

10 hours ago, Ksarul said:

I usually use Unicorn, Mouser, or Digi-Key for parts orders, as they all generally buy their stocks from the OEM. That generally minimizes the chance for bad parts.

I like Mouser, but this time neither Mouser nor Unicorn had all the parts I was needing.  fortunately, I obtained what appear to be good DRAM chips, so not all was a loss.    It does make me wonder how many others have been burned by the substandard parts; fortunately, I had older parts around that I could use to troubleshoot as I doubt I would have solved the issue without them, since replacing a suspect new part with another new part got me nowhere...

[+InsaneMultitasker]

Linking another topic here for future reference.

 

[Swim]

Have been trying to organize the TI/Geneve stuff I still have here and came across some MYARC FDC and Geneve boards. Of course as far as I can tell so far these boards are not working boards. I did spend some time today with what looked to be an FDC just like it came from MYARC. After playing with it for a while I found the 74LS245 was fried and replaced it with a new one. This got me to the system being locked up with a cyan screen when I powered up the TI. After about 4 hours and a new PAL and EPROM updated to version 1.5 and a new 70 nano second RAM chip just for heck of it the card is as you see it in the image and working very nicely with 5.25 disks and I'm guessing will work just as well with 3.5 disks but I don't have 3.5 drives hooked up to my TI repair system. Now that the card is working I'm thinking it should have both original electrolytic capacitors replaced. If anyone is interested in this FDC I'm asking $150.00 + shipping. Contact me here privately if interested.

[Swim]

9 hours ago, Swim said:

Have been trying to organize the TI/Geneve stuff I still have here and came across some MYARC FDC and Geneve boards. Of course as far as I can tell so far these boards are not working boards. I did spend some time today with what looked to be an FDC just like it came from MYARC. After playing with it for a while I found the 74LS245 was fried and replaced it with a new one. This got me to the system being locked up with a cyan screen when I powered up the TI. After about 4 hours and a new PAL and EPROM updated to version 1.5 and a new 70 nano second RAM chip just for heck of it the card is as you see it in the image and working very nicely with 5.25 disks and I'm guessing will work just as well with 3.5 disks but I don't have 3.5 drives hooked up to my TI repair system. Now that the card is working I'm thinking it should have both original electrolytic capacitors replaced. If anyone is interested in this FDC I'm asking $150.00 + shipping. Contact me here privately if interested.

This board has been taken. Stand by as I'll have a few more of these available as time allows. Haven't setup a P-Box yet to start testing what shape the Geneves are in.

[+InsaneMultitasker]

This weekend I finished installing a NOS power supply into my ancient Geneve tower case. (Some day I want to redo it using an 838 PEB).   As most projects go, one change spawned another 15 or so.

 

After I removed the old supply from the case (it was still functional) I opened it up and looked inside.  There were four or five capacitors bulging and/or leaking.  I set the power supply aside and installed the new one into the case.  I soldered a 24-pin ATX connector to the PEB backplane wiring so that I didn't have to cut the new power supply's connector. After some validation tests, I powered up the Geneve. 

 

What I noticed right away is that my old 8CM515 monitor produced a crisp, clear output; there was no interference or waviness.  The monitor has a few issues and is on its last legs, so a clear picture was the last thing I expected.  I am guessing that the old supply was putting out a lot of noise due to the failing caps and/or its age.  Before I attribute the problem solely to the power supply, I need to test with another system and monitor. Still, it is something for us to keep in mind.

 

The next phase was to migrate my development system back into the PC tower case from the PEB.  The system consists of a Geneve, SCSI card, HFDC, two ramdisks, TIPI, RS232, and Myarc FDC.  As I started experimenting with card placement in the tower, I found it very difficult to get all of the cables satisfactorily routed to the various drives. And if I needed to test a different configuration, pulling things apart was going to be an ugly mess.  I opted to continue with my PEB system for this development cycle, sans the Myarc HFDC. (The external power supply for the MFM and floppy drives failed not too long ago). I'll revisit my setup after the next release. 

 

I removed one of my two 5.25" drives from the PEB and replaced with a 3.5" drive. It took me a while to figure out that this drive had a drive selector for DS0,1,2,3.    After 25 years, I guess I had set-it-and-forgotten-it.  Tomorrow, I will wire up a power adapter for my EZ135 drive so that I can use that device for OS tests.

 

One last thought for those of you with battery-operated devices like the Horizon RAMdisk:  if you haven't checked your batteries in a while, take a moment to inspect them.   While I did not have any leaking batteries, my Horizon Ramdisk 3000 uses alkaline batteries that are close to needing replacement.  I haven't used my Geneve since last summer, so there has been a constant draw for months. 

 

 

[jbdigriz]

Thanks for these recent posts, everyone. Finally getting things organized around here and all the info will be useful getting a Geneve going again.

[+InsaneMultitasker]

I've been using my Geneve system a bit during the past few weeks.  With it being so hot outside, it seemed like the perfect time to back up the ramdisks' files and check their batteries.

 

(Note: don't check the batteries before backing up the ramdisk, lest you disrupt the circuit and lose or corrupt files!)

 

Both RAMdisks are 8MB capacity, populated with 16 x 512K low power SRAM chips.  The 3000's standard alkaline batteries are still supplying 4.1v after all the system downtime, and as far as I recall it has been 2.5+ years since I last replaced them.  I'll check them again in the fall and replace at the 3 year mark.  The 4000 runs on rechargeable nicad batteries and their output is at 3.4v. This might be on the low side, I need to check the specs to confirm.

 

The only challenge I faced was that the battery in my multimeter had to be replaced before I could test the batteries.  

 

[+OLD CS1]

2 hours ago, InsaneMultitasker said:

The only challenge I faced was that the battery in my multimeter had to be replaced before I could test the batteries.  

Some "Inception" shyte happening here...

[F.G. Kaal]

On 12/17/2020 at 11:29 PM, InsaneMultitasker said:

If you are using the extender card, check the voltage at the DRAM after receiving a bad cpu message. Confirm 5v.

Check continuity between DRAM chips. Some pins are not common to all chips.

Possibly bad DRAM / VRAM socket

For many of the DRAM chips to go bad points to possibly removing the card out of the PEB or rocking it in the slot with the PEB still on at some point in time.

I have a second Geneve 9640 wich booted MDOS 7.40 just fine. I was busy solving some SCART cable issue when all of a sudden I got the "BAD CPU RAM" error message. 

 

Following some tips from this topic didn't solve the problem:

1) Build the DramArduino to test the DRAMS: All okay

2) Swapped the 74LS245 bus driver: No change

 

Then I found a problem with the 7805 voltage regulator (M76) close to the CPU DRAM chips. This one got very hot. The voltage regulator problem is also mentioned in this topic by the way! After a few minutes the output voltage of this regulator dropped to 3.1 Volt. After swithing the PEB off for a few minutes to let things cool down  I could boot MDOS again.

 

This can be easely fixed by replacing the voltage regulator(s).

 

[+InsaneMultitasker]

7 hours ago, F.G. Kaal said:

Then I found a problem with the 7805 voltage regulator (M76) close to the CPU DRAM chips. This one got very hot. The voltage regulator problem is also mentioned in this topic by the way! After a few minutes the output voltage of this regulator dropped to 3.1 Volt. After swithing the PEB off for a few minutes to let things cool down  I could boot MDOS again.

 

This can be easely fixed by replacing the voltage regulator(s).

This is a common problem with the original Geneve cards, especially those without heat sinks or without thermal compound between the heat sink and regulator.  Be sure to use both with your replacement, unless you decide to use the DC-to-DC converters as discussed in prior posts.  The DC-to-DC converters are cool to the touch.

 

The VDP RAM on the other side of the card is subject to eventual failure, especially the chip adjacent to the regulator.  A proper heat sink will mitigate the heat issue in most cases.  I replaced the regulator with a DC-to-DC converter on my 24/7/365 Geneve because the VRAM kept failing over time.  This is especially noticeable with Extended BASIC and other VDP-intensive programs.  And since most disk DSRs also use VDP, failure can cause file content corruption in extreme cases.

[+mizapf]

So was my Geneve already improved when I bought it in 1990? (concerning the heat sinks, not the battery or SRAM expansion, that was me)

[+InsaneMultitasker]

2 hours ago, mizapf said:

So was my Geneve already improved when I bought it in 1990? (concerning the heat sinks, not the battery or SRAM expansion, that was me)

Improved enough for the card to operate under general usage.  The regulators are original components.  The two heat sinks may have been added at build time or later, in response to the failures experienced by other owners without proper heat sinks.  The regulator above the LED is missing a heat sink but you can see that someone scraped away the blue/green top layer, which may have been an intentional attempt to let the card draw away some of the heat.(Not a good idea).  It is hard to tell from the picture but I would guess (and expect) the capacitors are original parts as well. 

[+mizapf]

The funny thing is that I cannot really be certain that it wasn't me who put the heat sinks under the regulators. After such a long time, you really don't recall every screw turn. 🙂

[RickyDean]

On 6/2/2022 at 12:17 AM, mvancopp said:

I have used 8 of these buck converters:

10PCS DC-DC 12-24V To 5V 3A Step Down Power Supply Module Voltage Buck Converter | eBay

 

10 pcs = $10.95 + $1 for shipping.

 

Example: I have replaced the 7805 TI PEB side) on the Myarc 512 card with one of these. It runs very cool, almost no heat. I also removed the externally supplied 7805 and "OR'ed" the external and PEBox supplies using the card's existing diodes that are in-line with the power traces. This allows the single buck regulator to work with either supply (I used a regulated 9 volt 1 amp supply and the PEBox supplies about 11.5 volts). When the two 7805s were used the external 7805 got very hot. This is a simpler, more cost effective, and prevents the two regulators from "fighting" each other. 

The buck converters above are adjustable (variable) but also have a fixed mode for 3.3, 5, 9, and 12v.  believe they adjust up to 24v and supply up to 3A. They default is variable. To use the fixed mode you must cut the small trace connecting the variable option and use a solder bridge or a jump to select the fixed option. I put header pins on them and can drop them in place of the 7805s. I have also used these to power my HDs for the HFDC. They work great, again with virtually no heat and they are far more efficient then the power/heat waste of the 7805s.

 

I hope this helps and may save you some time.

 

Mark

 

@mvancopp Are these buck converters, still doing well in your system? I'm delving into the possibility of using them on my stuff.

[mvancopp]

2 hours ago, RickyDean said:

@mvancopp Are these buck converters, still doing well in your system? I'm delving into the possibility of using them on my stuff.

Hi @RickyDean,

Yes these are still working fine and I have used them in many things now. Be aware that the Ebay ones listed here have an input (unregulated side) limit of 17v. This works fine for the 5v in the PEB but not the 12v. That has an input voltage that is in the 24v range (this varies with load). For the 12v side a less expensive 7812 linear replacement I found is the VXO78012-1000 by CUI; available at Digikey at $2.95 each when less than 10 qty, https://www.digikey.com/en/products/detail/cui-inc/VXO78012-1000/7350298. These have an input limit of 36v like the 7812. There is also a 5v (VXO7805-1000 I think) version if you would rather use a name brand item with a 36v limit, more expensive but your peace of mind might be worth it or higher input limit might be worth it.

 

FYI warning for anybody using the Ebay 5v ones above. They default to adjustable using the pot you see in the Ebay pics OR they can be fixed. You must adjust prior to using them so you don't do any damage (obviously). For the fixed outputs you must cut an the etch seen to the right of the ADJ pads in the Ebay pictures and then solder bridge the fixed voltage you want. Ohm these out to be sure the ADJ is cut and the bridge is good, otherwise you will get strange voltages.

[RickyDean]

On 4/21/2021 at 10:59 AM, RickyDean said:

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, these has been on hold since 2021, but I've got time, I 'd like to finish and see about getting this bad boy up and running. Can you answer this question for me at this time? I think getting these two wires connected was the last of the work on getting this PFM+ system back together and hopefully running. The post was on page 21.

 

[+InsaneMultitasker]

16 minutes ago, RickyDean said:

hese has been on hold since 2021, but I've got time, I 'd like to finish and see about getting this bad boy up and running. Can you answer this question for me at this time? I think getting these two wires connected was the last of the work on getting this PFM+ system back together and hopefully running. The post was on page 21

Please remind me via PM this weekend.  I'll look for my old notebook and read the old posts at that time. The PFM+ was typically installed together with a 128Kx3 upgrade. Without reading the old posts, it isn't clear to me why you moved the LS138 and/or LS139.

[RickyDean]

6 hours ago, InsaneMultitasker said:

Please remind me via PM this weekend.  I'll look for my old notebook and read the old posts at that time. The PFM+ was typically installed together with a 128Kx3 upgrade. Without reading the old posts, it isn't clear to me why you moved the LS138 and/or LS139.

I'll have to reread too, but the idea was to move the 138 and 139 from the top of the sound chip for access, and all my chips can be easier to replace, at the same time. Thanks