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FarmerPotato

Bringing up "Geneve 2020": Debugging Help Please!

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Building copy #2 of the BIOS memory card. This is why the prototype shop sends you 3 copies!

 

I test powering up frequently. So far current consumption is up from 450 mA to 590. The SMD are all powered up with a lot of floating inputs. The '645s on the data bus suck 100 mA as the CPU hopelessly tries to get instructions.  I think that will go down when ROM/RAM are connected to the data bus buffers. 

 

Other chips, not using much power.  The rest of the 40mA is from address bus and decoding: '645, 645, 645, 125, 138, 157. A few floating inputs there. 


My VirtualBench power supply goes to 5V 1A, and I'm worried it will reach the limit with more cards. At that point, I will disconnect its 5V, and plug in the wall wart again.

 

From the 1st card build, I removed a bunch of parts, so the short is isolated to the SMD chips, or the RAM sockets. Most likely, I damaged the PCB under the RAM sockets when I tried solder paste and had to unsolder that.

 

 

I tried to salvage the ZIF sockets, and for the first time I yanked out vias! These pins had stubborn cold solder joints, and I'm out of that magic stuff that alloys with old solder, so I applied force.

 

IMG_4293.jpeg.e62a6d85679086da719f327cd72ef6be.jpeg          <- Coppery vias         Owl Pellet ->     IMG_4292.jpeg.5e0e62128d6e453f9aa4a1232376cf92.jpeg

 

The right picture is what came out of the desolder tool. I haven't cleaned it during this job. The suction started to fail after 1 ZIF. I ejected the "solder pipe", which stores the sucked-out solder. Found a large cone of solder bits, sintered together! (I crumbled it before I got a picture of Vesuvius, so I'm calling it Owl Pellet now.) The metal disc is probably salvageable (there's a disposable filter under it), but I put in a new one anyhow.  Also, the desolder tip was clogged (a cone with a hole in the tip), and I could not unclog it.

 

Lesson: just clean the tool before using it, every time. It has served well for years.  Time to reorder the filters. 

 

 

 

 

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Installed the two Flash ROMs. Current consumption of those is 150+100 mA. And with that, it is pushing the 1A limit. The CPU is running code, but poorly, with no RAM.  It is not going to run on this 1A power supply.

 

Time to put the PicoPSU back in. It is the 80W model, the smallest.  I estimated 25W for everything I'm going to put in.

 

With the PicoPSU, I lose the ability to measure DC current... hmm, I have a KillAWatt I could use to get the AC power.

 

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1 hour ago, FarmerPotato said:

With the PicoPSU, I lose the ability to measure DC current... 

Could you get/put a low resistance shunt somewhere and compute the current?

 

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5 hours ago, FarmerPotato said:

I tried to salvage the ZIF sockets, and for the first time I yanked out vias! These pins had stubborn cold solder joints, and I'm out of that magic stuff that alloys with old solder, so I applied force

That's the stuff nightmares are made of with the "delicate" iteration of Geneve PCBs.  You can almost blow the pads and vias from those boards!  I've had some luck applying small diameter solder (the stuff that is close to threadlike) to the stuck pins before desoldering, and if I notice one or more stubborn joints on the same component I'll resolder them all first before desoldering. Your picture also reminded me of this old article that I had found interesting...

 

https://medium.com/supplyframe-hardware/confessions-of-a-pcb-designer-anatomy-of-a-via-f1d6aec236ec

 

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2 hours ago, InsaneMultitasker said:

That's the stuff nightmares are made of with the "delicate" iteration of Geneve PCBs.  You can almost blow the pads and vias from those boards!  I've had some luck applying small diameter solder (the stuff that is close to threadlike) to the stuck pins before desoldering, and if I notice one or more stubborn joints on the same component I'll resolder them all first before desoldering. Your picture also reminded me of this old article that I had found interesting...

 

https://medium.com/supplyframe-hardware/confessions-of-a-pcb-designer-anatomy-of-a-via-f1d6aec236ec

 

That was fascinating. And free!

 

 

 

I want to take a closer look at these PCBs, made at Aisler.net.  

 

Vias: 

 

Via2.png.78b79401c6ad7d162ce5a58cb1b3ab70.png

 

Plated Thru-hole via (PTHV) (2.54mm pitch DIP)

 

PTH.thumb.png.3734b242ae89363ab0a4c868e28fa632.png

 

Here's a closeup of the pulled-out via:

PulledVia.thumb.png.1a359f4f882489303e93864c87920e4e.png

 

Vias look coppery. PTHV looks nickel-y, same as its pad.

 

Estimates relative to the known 2.54mm thru-hole pitch:

Via diameter 0.35 mm.    Kicad said drill 0.40 mm 

PTHV diameter 0.90 mm.   Kicad said drill 0.80 mm (pad is 2.4 x 1.6 mm oval)

Checks out.

 

Parameters at Aisler.net "Beautiful Boards Budget 8-day service" 

Surface finish: HASL, lead-free ("Hot Air Surface Leveling")

IPC Classification: 2.  (from that blog, 1=toy, 2=consumer, 3=critical. Aisler can do 3.)

Minimal Drill diameter: 0.45 mm

 

$25 for 3x 100x100mm, that is $1.50/3/sqin. My 50x100mm boards were $2/3/sqin.

For ENIG it costs 2x, or 3x for ENIG and 2-day service 

 

Compare OshPark at $5/3/sqin all sizes, looks like ENIG and their purple solder resist doesn't scratch.

 

 

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6 hours ago, TheBF said:

Could you get/put a low resistance shunt somewhere and compute the current?

 

Aha, there is a perfect spot for that on the motherboard: a power switch terminal I'm not using!

 

 

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I don't get why this board draws more power than the wire-wrap version. That version lacked the bus buffers/drivers, and the PLD. The WW version had the same two Flash ROMs and static RAMs, and consumed about 300 mA.

 

The current of this board went up 250 mA just from the two flash ROMs. 550+ mA in all. 

 

It runs, sort of, with the RAM installed. Current is maxed out at 1A, and supply voltage drops to 4.5V. The CPU seems to keep at it, but it is getting >FFFF back from reading the ROM. 

 

I have a 8-pin SOIC test clip, and that's going to have to suffice for testing. 


Still hunting for that darn 12V 5A brick for the picoPSU. Not sure what happens if I find a 12V 3A, but draw too much from the supply. They do rate this picoPSU at 85W, but ship it with a 60W adaptor.

 

Edited by FarmerPotato
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