How to find damaged trace? [SOLVED]

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mikro
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How to find damaged trace? [SOLVED]

Postby mikro » Fri Jun 11, 2010 5:16 pm

Hello,

I've noticed a few posts how people damaged their Falcons while replacing NVRAM and yes, I belong to them :) It seems I damaged some path / trace on MB since NVRAM chip is working (checked on another falcon), I can measure +5V on pin 1 and 24, GND on pin 12 is working, too. And I used beeper to check connectivity from back side to front side for each pin.

Basically, Falcon don't start, monitor produces "going to sleep" (different from "out of scan range"). I tried to compare working Falcon without NVRAM and this damaged one without NVRAM, I noticed only one difference: working Falcon constantly reboots with "going to sleep" while damaged one does it only once.

Looking into Falcon schematics, I don't see U64 anywhere, do you know what should I check? I.e. where pins from NVRAM lead? I assume the most probably I burned out some hole (I'm not big de-soldering expert, soldering was done by professional guy), even when I used good soldering iron and not much heat...

This post viewtopic.php?f=27&t=18846&hilit=falcon+schematics&start=25#p166748 mentions U64/Pin13 RTCCS <-> U56/Pin75 trace, what else I could check?

Any help appreciated!
Last edited by mikro on Sun Jun 27, 2010 1:40 pm, edited 1 time in total.

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Re: How to find damaged trace?

Postby mikro » Fri Jun 11, 2010 6:39 pm

OK, it took some time, I downloaded Dallas chip pinout, found 6850 in schematics, carefully written down their D0 - D7 signals. When I checked MIDI ACIA D0 <-> Keyboard ACIA D0, I've got a sound (beep). When I checked ACIA D0 <-> Dallas D0, nothing. Broken trace you say? I tried it on working Falcon and -- the same result! I don't understand how it's possible? I double checked I connect right pins (pin 4 on Dallas to pin 22 on ACIA) so here shouldn't be error. I can't understand why I don't hear any beep on working Falcon? Isn't possible it's another data bus? Rodolphe recommended me this check (keyboard ACIA data bus -> Dallas data bus).
Last edited by mikro on Fri Jun 11, 2010 7:40 pm, edited 1 time in total.

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Re: How to find damaged trace?

Postby mikro » Fri Jun 11, 2010 7:38 pm

Finally some success. I was able to use Videl as source for data bus connection and I discovered D5 is dead on U64, good. That ACIA remains mystery for me. What's worse, now I don't know where to get that D5, I certainly can't solder on Videl/Combel, not with my (lack of any) experiences. Is there any other source on simpler chip other than ACIA? Or do you think it's safe to solder it on ACIA's D5 even when I can't measure connection?

Simbo and others, I would really appreciate your great knowledge now :)

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Re: How to find damaged trace?

Postby lp » Fri Jun 11, 2010 7:41 pm

I worked in electronics for many years, about 12, and when all else failed I used a very good magnifying glass and my eyeball. We had small eyepiece things, forget the proper term. Best of luck finding it.

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Re: How to find damaged trace?

Postby mikro » Fri Jun 11, 2010 9:57 pm

ACIA mystery solved, it's true both have 8bit data bus but the difference is one use upper 8bit while second (U64 and friends) the other side :)

Anyway, I tried to connect wire from SCC's D5 to U64's D5, no success. According to Rodolphe, this U64 is write-trough, i.e. it's not terminal (no idea about the right term ;-) so I assume that D5 isn't "forwarded" to some other chip.

Stay tuned :)

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Re: How to find damaged trace?

Postby wongck » Sat Jun 12, 2010 4:54 am

Well, for people like myself who cannot do soldering to save my life, I would just do what I did to my Falc to recover the NVRAM.
Basically cut one leg and solder 2 wires to the chip as written in my webpage. :mrgreen:

Sure easier than to unsolder 24 pin (from multi layered PCB :roll: ) and then solder it back.
Total soldering is around 48 points.
So i need to do around 5% soldering ( 2 out of 48) and none of these 2 are for multilayered - just normal solder blob.
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Re: How to find damaged trace?

Postby enito » Thu Jun 24, 2010 3:34 am

Hi, in my case for fix the nvram nightmare was checking all the u64, contacts, i checked this check list:

64/Pin1 Power 5V
U64/Pin2 not connected or not used
U64/Pin3 not connected or not used
U64/Pin4 AD0 <-> U31/Pin41
U64/Pin5 AD1 <-> U31/Pin42
U64/Pin6 AD2 <-> U31/Pin43
U64/Pin7 AD3 <-> U31/Pin44
U64/Pin8 AD4 <-> U31/Pin45
U64/Pin9 AD5 <-> U31/Pin46
U64/Pin10 AD6 <-> U31/Pin47
U64/Pin11 AD7 <-> U31/Pin48
U64/Pin12 GND
U64/Pin13 RTCCS <-> U56/Pin75
U64/Pin14 RTCAS <-> U56/Pin76
U64/Pin15 RXW <-> U24+U52/Pin13
U64/Pin16 not connected or not used
U64/Pin17 RTCDS <-> U56/Pin55
U64/Pin18 is connect to C232, R243 and D11 on the motherboard backside
U64/Pin19 not connected or not used
U64/Pin20 not connected or not used
U64/Pin21 not connected or not used
U64/Pin22 not connected or not used
U64/Pin23 not connected or not used
U64/Pin24 Power 5V

In my case, was a bad trace and no get 5V, i hope this guide can help you..

greets

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Re: How to find damaged trace?

Postby mikro » Thu Jun 24, 2010 7:01 am

enito, I've made quite a progress, I was able to cross-check all U64 pins (D5 is the only one fault) but as I said, it's not terminal, so my further check uncovered 3 missing traces to EPROM chip (TOS) data bus. Hopefully in following days I will be able to re-connect them again (poor MB :) and it will start working. If not, there's another trace(s) between U64 and some Falcon part (SDMA probably?). Let's hope this wont be the case :)

simbo

Re: How to find damaged trace?

Postby simbo » Sat Jun 26, 2010 4:23 pm

ive had to resolder the eprom sockets a few times seems sparce on solder when flowed

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Re: How to find damaged trace?

Postby mikro » Sat Jun 26, 2010 4:55 pm

Currently, situation looks really bad. I've checked every trace from / to NVRAM and TOS, repaired broken ones and that damned Falcon still wont boot, it seems like video output even isn't active but I can measure +5V on NVRAM + fan is working so ... Jookie brought oscilloscope here, so we try something but I'm very sad about it :(

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Re: How to find damaged trace?

Postby wongck » Sun Jun 27, 2010 1:44 am

Mikro... sounds bad.
What ever you're trying, hope it works for you... Good Luck !!
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Re: How to find damaged trace? [SOLVED]

Postby mikro » Sun Jun 27, 2010 1:32 pm

OK, so it seems fixed (knock-knock). To sum my adventure up + to possibly help others in a future I try to compile some hints about NVRAM and Falcon repair in general.

1. Never try to mess with Falcon hardware, especially meaning soldering work, if you are not very experienced. Having skill like "I can solder something here and there" is simply not enough.

2. Even if you are experienced iron man :), keep in mind Falcon has multi-layer PCB and its contacts can be destroyed not only by scratches but also by much heat from soldering iron! (my case)

Ok, so even although you were careful (I was not) with soldering iron, something stopped to work after NVRAM replace (better said, after NVRAM -> socket+NVRAM replace).

3. Download NVRAM (Dallas) datasheet (attached) and Falcon schematics (from http://www.janthomas.org.uk/files/falcon.zip). Identify and check basic things on NVRAM -- +5V on pins 1/24, GND on pin 12.

4. Check further things -- 3 signals from Combel (see post from enito or check Falcon scheme for RTCxx signals) to NVRAM, data bus (d0-d7) connection (against Videl, Combel, CPU, ... whatever you like) to NVRAM, RxW signal (anywhere on Falcon MB). Be careful with data bus on ACIAs, as they have d0-d7 but they are upper 8bits, not lower !!! So don't use them for connection validation.

5. Now, tricky thing. TOS (EPROM) is connected on NVRAM data bus, not general Falcon one!!! So you must check d0-d7 from NVRAm to TOS! Rodolphe was not sure but it's possible SDMA chip is also connected to NVRAM and not general data bus.

6. Ok, now you should have some broken traces found. How to repair: if it's easy soldering (like signal from NVRAM), solder it on front or back side of MB, as appropriate, there's no problem with that. Problems begin with destinations -- from NVRAM. For example, soldering on Combel, TOS chip (with very small pins)... it's worth checking if there isn't some hole near the pin connected to it, i.e. you wont solder on pin itself but on the hole, you can use back side of MB then, too. Very useful.

7. You've done all soldering and still not working. Very important thing: check everything again. It's not empty words, I really mean it, best to let it check to someone else than who did the soldering / first checking. Everything from good connections between damaged traces to right number of pin (!).

8. Checking: it's more or less safe to use "beeper" to check, at least for data and control signals, I didn't destroy my Falcon with that :) But for checking on CPU, FPU, GALs, ... better use resistance measuring, i.e. if you see unlimited resistance => no trace, ~0 Ohms resistance => working trace.

9. Ok, you're sure everything is connected and Falcon still shows nothing, time to check if reset signal is delivered to CPU and if some most important chips receive their clocks. In Falcon schematics archive is very useful diagram by Rodolphe showing clocks in Falcon with connections and values. Very useful to check. Also AS signal on CPU is useful to check, if you get 1-2 UPs and then nothing, it's bad (access fault reading TOS ROM).

10. You receive all clocks, see reset signal when measuring and still not working? It's possible some pins / contacts on chips seems to be ok, when you push them, you receive values but as soon as you get your hands out, chip is disconnected. I recommend to let Falcon running and try to push / knock on MB / chips and to see if something doesn't change. Sounds silly? It shouldn't, it's true!

So, this is what I learned here. Used stuff: multi-meter device, Falcon schematics, Dallas data sheet, Rodolphe's clock diagrams, oscilloscope. Short summary of my problems / causes:

- I suck at soldering :)
- trace D5 from NVRAM to data bus was broken
- trace from D5-D7 from NVRAM to TOS EPROM were broken
- RTCDS from Combel to NVRAM was broken (found after 3rd check in totally hopeless mood!)
- RTCDS from Combel to NVRAM was soldered on Pin18 instead of 17 ;-)
- XRESET from U11 to CPU wasn't delivered (measured by oscilloscope), we didn't solve this mystery, it got fixed after next step, probably some side effect
- Pin12 (GND) on NVRAM was badly soldered (good contact only after push / knocking on MB)

You see, quite horror. NEVER try to solder if you can't do it!!! NEVER !!!

I want say public and huge thank you to -XI-/Satantronic for his excellent soldering skills, Jookie for his useful and pragmatic point of view on our work ("hey, here's the bug, ok, next will follow, don't worry" :) and amazing ability to deduce things from foreign schemes for foreign hardware (he didn't do any work on any Falcon before, not even change of hard disk :) and of course Rodolphe Czuba for his useful tips what to check (we would never find out TOS EPROM is behind NVRAM for example).
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Re: How to find damaged trace?

Postby bladeomega » Wed Jun 30, 2010 11:52 pm

enito wrote:Hi, in my case for fix the nvram nightmare was checking all the u64, contacts, i checked this check list:

64/Pin1 Power 5V
U64/Pin2 not connected or not used
U64/Pin3 not connected or not used
U64/Pin4 AD0 <-> U31/Pin41
U64/Pin5 AD1 <-> U31/Pin42
U64/Pin6 AD2 <-> U31/Pin43
U64/Pin7 AD3 <-> U31/Pin44
U64/Pin8 AD4 <-> U31/Pin45
U64/Pin9 AD5 <-> U31/Pin46
U64/Pin10 AD6 <-> U31/Pin47
U64/Pin11 AD7 <-> U31/Pin48
U64/Pin12 GND
U64/Pin13 RTCCS <-> U56/Pin75
U64/Pin14 RTCAS <-> U56/Pin76
U64/Pin15 RXW <-> U24+U52/Pin13
U64/Pin16 not connected or not used
U64/Pin17 RTCDS <-> U56/Pin55
U64/Pin18 is connect to C232, R243 and D11 on the motherboard backside
U64/Pin19 not connected or not used
U64/Pin20 not connected or not used
U64/Pin21 not connected or not used
U64/Pin22 not connected or not used
U64/Pin23 not connected or not used
U64/Pin24 Power 5V

In my case, was a bad trace and no get 5V, i hope this guide can help you..
greets


Good work enito.
Last edited by bladeomega on Fri Jul 02, 2010 12:42 am, edited 1 time in total.

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Re: How to find damaged trace? [SOLVED]

Postby enito » Thu Jul 01, 2010 12:36 pm

thx :) i hop this info can help another guy ,

regards!

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Re: How to find damaged trace? [SOLVED]

Postby bladeomega » Thu Sep 16, 2010 11:14 am

enito wrote:thx :) i hop this info can help another guy ,

regards!


Here are some news about nvram fixing too.
http://forum.atari-home.de/index.php?topic=7055.msg47161#msg47161

http://forum.atari-home.de/index.php?topic=5846.msg34519#msg34519

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Re: How to find damaged trace? [SOLVED]

Postby Atari030 » Mon Jan 26, 2015 7:18 am

This just saved me god knows how long studying the Falcon schematics. Brilliant. Pin 14 of my Dallas chip wasn't very forthcoming, thar she is RTCAS.

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Re: How to find damaged trace? [SOLVED]

Postby bladeomega » Sat Nov 07, 2015 12:50 am

Yeah, it's a nice checklist.

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Re: How to find damaged trace?

Postby fenarinarsa » Tue Oct 09, 2018 10:55 pm

enito wrote:Hi, in my case for fix the nvram nightmare was checking all the u64, contacts, i checked this check list:

64/Pin1 Power 5V
U64/Pin2 not connected or not used
U64/Pin3 not connected or not used
U64/Pin4 AD0 <-> U31/Pin41
(...)


OMG thanks a lot for the checklist, I just changed the NVRAM and my Falcon didn't boot (with no video at all). It turned out I made a bad solder
joint on pin 14 and that the trace from U64/Pin11 to U31/Pin48 was damaged.

Now my Falcon boots perfectly <3

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Re: How to find damaged trace? [SOLVED]

Postby frost » Wed Oct 10, 2018 10:05 am

Thanks for "up-ing" this topic, I have a Falcon with some NVRAM problems. The NVRAM has been changed by the former owner - but I would have made the same result and I can't write the NVRAM correctly anymore.
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