Need help diagnosing my PAL Amiga 500+

[SamBushman]

Hi gang. About a month ago I bought an Amiga 500+ off eBay. It had a battery that exploded, but didn't appear to have too wide-spread of damage. I've managed to clean up almost all the corrosion and bodge a couple traces that were broken. However, I still can't get my poor Amiga to fire up successfully. Work I've done on it so far:
1. Replaced all capacitors on the board.
2. Socketed and replaced U12 due to heavy corrosion on the pins
3. Socketed and replaced U38 and U39 as part of trying to resolve serial issues I'll explain below
4. Verified Paula, Gary, Odd CIA, and Even CIA all operate well in an existing A2000 I have access to.
5. Verified all expected traces connecting Chip RAM, Agnus, CPU, Paula, both CIAs, ROM, and the serial port have conductivity using my multimeter.
6. Reflowed the serial port
7. Verified there are no shorts at the power supply connection port (implying none of the rails on the board are shorting either)

Despite this I get a green screen when attempting to boot the kickstart ROM and the following when attempting to boot with a DiagROM:

Serial output:

[00][1B]gs5ra aa>fau b tDA

[S e[

0rOoat0 0F1m50 10 11F1DF0d01e00 1

 000A0 1F1 51 10 11F1[1B]F0:01e00 1

 000A0 0F1m50 10 11F1D00d11e00 1

 000F0 0F1m50 10 11F1D00a11t10 1

 0F0F0A0F0151 11 11F1E00a11i10 1

 0F0 0A1F0151 11 11F1E00e11i10 1

00F0 0A1F0151 11 1101LF0e11i1001

00F0 0A1$13$1 10 1100LF1R11r1001

00F0 4A0$1[$0 10 1100IF1R11r1001

00F0m4A0$1[$0 10 1100IF1R11r1001

00F0m4A0$1[$0

11

1100A01 11W10F1m00$014A0$0[1B]$0

11

11F0A01 11W10F1m00F014A0$0[1B]$0

11

11F0A01 11 10F1000$014A1 0[1B] 1

11

10F0F01 10 10F1000$030A1 00 1

 1

 0F0F01 10 10F1000$038A1:10:1

 1

 0F0F01 10 11F1[00$0[0A0:10:01 1

 0F0 F1 10 11F1[1B]00$0[8A0d10e01 1

 0F0 F1 10 11F1[1B]00 0[9A0d10e01 1

 0F0 F1 10 01F1[1B]00 0[1B]9A0a11t11 1

 0F0m01 10 01F1D00:00AA1a11t10 1

 0F0m01 10 01F1D00:0[1B]AA1a11t10 1

 0F0m01 10 01F1E00:00BA1e10i1051

00F1100 10 01F1E00d000A1e10i0051

00F1100 10 01F1E00d100A0e10i0051

00F1100 10 01F1L00a100A0R10r0151

00$13$0 10 01F1L00a100A0 11W1151m01$13$0 10 01F1I00a100A0 11W1151m01$1[$0 10 01F1I00e100A1 11W10510F1$1[1B]$0

11

0101A00R100A1 11 10510F1$1[1B]$0

11

0101A00e100A1 11 10510F1$1[1B]$0

11

0001F00R100A0 10 00F1[01 10 0

11

0001F00 100A0 11 11F1D01d11t11 1

 0F1100 11r$1 11

01F1FF0 11 10F1[1B]01:11e0

11

i11F1

50$13$1 11

00F1A01 11 00F10 01F1E50a11i00 1

F1F13$0 11 00F1L0 0F1 51 11 11F1D00d11t10 1

00F1m4A0$1[1B]$1

11

10F1 F1 11 11F1[1B]00 111A1e11r01F1m01$1[$0

11

00F1F00 11$A1 11 00F1EF1e11i11F1

00$1[$0 11d:0

 1

 0F1 00 11 00F1EF1a11i00 1

 01F1050 11 1

 1

 1F1 F1 11 00F1[1B] 01F1I51 11W00F1000$11 0

11

 0F1F0 0F1151 11 11F1IF1R11W10F1m00$1[0A0:11e01 1

 0F1m01 11 01F1L00a110A1 11 01F1[1B]01:11e01 1

 0F1m00 11 $1 11

00F1FF0 11 11F1[01:11:0

11

i01F1

50$13$1 11 00F1A01 11 00F1m 01F1D51a11t00 1

F1F13$0 11 00F1L0 0F1 51 11 11F1D00d11t10 1

00F1m4A0$1[1B] 1

11

 0F1 F1 11 01F1D00:111A0e11r01F1mF1$1[1B]$0

11

00F1F00 11$A1 11 00F1L01e11r11F1m01$1[$0 11d:10 1

 0F1mF0 11 00F1LF1e11r00 1

 11F1[50 11:10 1

 1F1 F1 11 00F1D 01F1I51 11 00F1000 11 0

 1

 0F1F0 0F1151 11 11F1IF1R11W10F1000$1[CA0d11t11 1

 0F1100 11 01F1I00e110A0 11 01F1[1B]01d11e01 1

 0F1100 11r$1 11

00F1FF0 11 10F1[1B]01:11e0

11

i11F1

50$1[$1 11

00F1A01 11 00F10 01F1E50a11i00F1

F1$13$0 11

00F1I0 1F1 51 11 11F1E00a11i10 1

00F114A0$1[1B] 1

11

 0F1 F1 11 01F1D00:11enm

- pAM

And the following on my monitor:
1. A flickering red screen
https://drive.google.com/uc?export=v...cLmLyddgUFg8He
2. A solid blue screen
https://drive.google.com/uc?export=v...We9_1RMhxdSfLp
3. A solid light grey screen
https://drive.google.com/uc?export=v...cDRBr4VXSNzVzo

I'm kinda stumped what the problem could be. I figure it's either:
1. A bad board (perhaps a short somewhere)
2. A bad Agnus
3. Bad Ram

Any suggestions on how to further diagnose?

[alexh]

https://www.amigalove.com/viewtopic.php?t=324

I'd say (1) you've got trace damage somewhere. Possibly vias going between the top and bottom of the board?

Start at the kickstart ROM and trace address and data lines back to the CPU and the chip selects from the custom chips? ROMEN signal (comes from Gary?)

High res photos of the board, top and bottom, especially around the battery might help.

[SamBushman]

Thanks for the suggestions so far. I'll recheck those tonight. Also, here are some images of the board:

https://drive.google.com/uc?export=v...3JBHGlzBNEZDwy

https://drive.google.com/uc?export=v...BH5Fx8BEg06S2K

https://drive.google.com/uc?export=v...FPVP98M1BRnr49

https://drive.google.com/uc?export=v...3l2OSCsnEvR4xB

https://drive.google.com/uc?export=v...tF8cbXf-Aj_DT4

[solarmon]

Looking at the pictures, there is still a lot of battery damage - it needs to be removed and cleaned up and the traces repaired. It is likely that one or more of the traces are broken or high resistance and need repairing and/or re-tinning.

[Hewitson]

Originally Posted by solarmon

Looking at the pictures, there is still a lot of battery damage - it needs to be removed and cleaned up and the traces repaired. It is likely that one or more of the traces are broken or high resistance and need repairing and/or re-tinning.

Yep. Looks like quite a few tracks to the immediate right of the battery location have basically vanished.

[SamBushman]

Hi gang, sorry for the long delay in reply. I've been testing traces on my board. I DID find a single broken trace connecting pin 18 of U9 (the CLOCK IC) to the resistor/diode blob next to the battery terminals. I installed a bodge wire to restore connectivity, but no change to behavior.

I've been testing all the components around the "splash zone" of the battery corrosion. I also tested all the pins on Gary (including the ROMEM line, address, and data lines). All appear to be connected and I've detected no unexpected shorts on Gary's pins. I've documented the resistance measured. Most traces are below 0.5 Ohms. Everything is below 1 Ohm. I don't know if any of these readings are wildly out of spec. Any advice would be appreciated.

Thanks again for your help so far!

Trace resistances
ROMEM -> R114 0.22 Ohms
R111 -> U13 Pin 11 0.12 Ohms
E106 -> R105 0.23 Ohms
E106 -> Ground 0.05 Ohms
R105 -> U33 Pins 2, 3 0.16 Ohms
E107 -> ground 0.07 Ohms
R916 -> JP9 0.13 Ohms
E102 -> JP9 via 0.08 Ohms
R103 -> U12 Pin 1 0.1 ohms
U12 Pin 1 -> U12 Pin 19 0.05 Ohms
R103 -> U10 Pin 1 0.17 Ohms
U10 Pin 1 -> U10 Pin 19 0.05 Ohms
R101 -> CPU Pin 10 0.31 Ohms
R112 -> U11 Pin 1 0.18 Ohms
R113 -> U11 Pin 1 0.13 Ohms
R915 -> via near battery 0.05 Ohms
R915 -> U9 Pin 2 0.2 Ohms
R915 -> VCC 0.15 Ohms
R102 -> clock 0.23 Ohms
C12 -> VCC, Ground 0.8 Ohms

Gary
Gary Pin 1 -> Ground 0.08 Ohms
R102 -> Gary Pin 2 0.11 Ohms
R112 -> Gary Pin 3 0.11 Ohms
Gary Pin 4 -> R113 0.08 Ohms
Gary Pin 5 -> RP501 Pin 5 0.19 Ohms
Gary Pin 5 -> JP1, Q711 0.12 Ohms
Gary Pin 6 -> VCC 0.07 Ohms
Gary Pin 7 -> EvenCIA Pin 17 0.14 Ohms
Gary Pin 8 -> Paula Pin 39 0.17 Ohms
Gary Pin 9 -> Paula Pin 38 0.17 Ohms
Gary Pin 10 -> Agnus Pin 51 0.28 Ohms
Gary Pin 10 -> CPU Pin 8 0.35 Ohms
Gary Pin 11 -> RP101 Pin 6 0.06 Ohms
Gary Pin 11 -> Agnus Pin 52 0.32 Ohms
Gary Pin 11 -> CPU Pin 7 0.35 Ohms
Gary Pin 12 -> Agnus Pin 22 0.3 Ohms
Gary Pin 12 -> CPU Pin 9 0.48 Ohms
Gary Pin 12 -> EvenCIA Pin 22 0.11 Ohms?
Gary Pin 12 -> OddCIA Pin 22 0.18 Ohms
Gary Pin 13 -> Agnus Pin 24 0.19 Ohms
Gary Pin 13 -> CPU Pin 6 0.33 Ohms
Gary Pin 14 -> CPU Pin 12 0.24 Ohms
gary Pin 14 -> RP104 Pin 6 0.3 Ohms
Gary Pin 15 -> Agnus Pin 20 0.19 Ohms
Gary Pin 16 -> EvenCIA Pin 13 0.21
Gary Pin 16 -> Floppy Pin 10 0.23
?Gary Pin 17 -> VCC 0.08 Ohms
?Gary Pin 18 -> Agnus Pin 23 0.18 Ohms
Gary Pin 19 -> Agnus Pin 19 0.19 Ohms?
Gary Pin 20 -> Agnus Pin 25 0.22 Ohms
R114 -> Gary Pin 21 0.1 Ohms
Gary Pin 22 -> U9 Pin 8 0.17 Ohms?
Gary Pin 22 -> RAMExp Pin 49 0.54 Ohms
Gary Pin 23 -> U9 Pin 10 0.24 Ohms
Gary Pin 23 -> RAMExp pin 50 0.21 Ohms
Gary Pin 24 -> Ground 0.05 Ohms
R111 -> Gary Pin 25 0.07 Ohms
E106 -> Gary Pin 26 0.07 Ohms
Gary Pin 26 -> R105 0.19 Ohms
Gary Pin 26 -> U33 Pin 2, 3 0.22 Ohms
Gary Pin 27 -> E107 0.09 Ohms
Gary Pin 27 -> Paula Pin 29 0.13 Ohms?
Gary Pin 27 -> R104 0.13 Ohms
?Gary Pin 27 -> U33 Pin 10, 11 0.22 Ohms?
Gary Pin 28 -> E108 0.07 Ohms?
Gary Pin 28 -> U35 Pin 15 0.24 Ohms?
Gary Pin 28 -> Paula Pin 28 0.13 Ohms?
Gary Pin 28 -> R103 0.12 Ohms?
Gary Pin 28 -> U33 Pin 5, 6 0.21 Ohms?
Gary Pin 28 -> Denise Pin 36 0.22 Ohms?
Gary Pin 28 -> U41 Pin 6 0.26 Ohms
Gary Pin 29 -> CN15 Pin 2 0.13 Ohms
?Gary Pin 29 -> RP104 Pin 9 0.31 Ohms
?Gary Pin 30 -> RP101 Pin 9 0.08 Ohms
Gary Pin 30 -> OddCIA Pin 2 0.16 Ohms
Gary Pin 31 -> CN15 Pin 3 0.12? Ohms
Gary Pin 31 -> RP104 Pin 8 0.31 Ohms
Gary Pin 32 -> JP7A Pin 2 0.1 Ohms?
Gary Pin 32 -> JP7B Pin 3 0.23 Ohms?
Gary Pin 32 -> RP501 Pin 9 0.25 Ohms
Gary Pin 33 -> RP105 Pin 8 0.08 Ohms?
Gary Pin 33 -> CPU Pin 45 0.22 Ohms?
Gary Pin 33 -> ROM Pin 33 0.26 Ohms
?Gary Pin 33 -> Agnus Pin 76 0.3 Ohms
Gary Pin 34 -> Agnus Pin 77 0.19 Ohms?
Gary Pin 34 -> ROM Pin 2 0.36 Ohms
?Gary Pin 34 -> CPU Pin 46 0.29 Ohms?
Gary Pin 35 -> Agnus Pin 59 0.25 Ohms?
Gary Pin 35 -> ROM Pin 1 0.3 Ohms?
Gary Pin 35 -> CPU Pin 47 0.3 Ohms?
Gary Pin 36 -> Agnus Pin 35 0.19 Ohms
?Gary Pin 36 -> ROM Pin 42 0.27 Ohms?
Gary Pin 36 -> CPU Pin 48 0.28 Ohms?
Gary Pin 37 -> CPU Pin 50 0.26 Ohms
?Gary Pin 38 -> CPU Pin 51 0.28 Ohms?
Gary Pin 39 -> CPU Pin 52 0.28 Ohms
Gary Pin 40 -> Ground 0.08 Ohms?
Gary Pin 41 -> Agnus Pin 16 0.29 Ohms
Gary Pin 41 -> CPU Pin 18 0.30 Ohms?
Gary Pin 42 -> CPU Pin 17 0.29 Ohms
Gary Pin 43 -> R101 0.09 Ohms
Gary Pin 44 -> U36 Pin 9 0.18 Ohms?
Gary Pin 45 -> U36 Pin 5 0.17 Ohms?
Gary Pin 46 -> U36 Pin 3 0.19 Ohms
?Gary Pin 47 -> U36 Pin 1 0.2 Ohms
?Gary Pin 48 -> VCC 0.35 Ohms??
RP105
10 -> Ground 0.09 Ohms
9 -> isolated
8 -> Gary Pin 33 0.09 Ohms
7 -> Gary Pin 34 0.09 Ohms, U12 via 0.13 Ohms
6 -> Gary Pin 35 0.09 Ohms
5, 4, 3, 2 -> Gary Pins 0.09 Ohms
1 -> VCC 0.14 Ohms

JP7A
3 -> Ground 0.03 Ohms
2 -> JP7B-1 0.2 Ohms
1 -> Memory Exp Via 0.15 Ohms

U12
Pin 1 -> R113 0.07 Ohms?
Pin 1 -> Pin 19 0.06 Ohms
?Pin 1 -> U10 Pin 1 0.09
?Pin 1 -> U10 Pin 19 0.12?
Pin 2 -> ROM Pin 15 0.23 Ohms
?Pin 2 -> U13 Pin 2 0.05 Ohms
?Pin 2 -> EvenCIA Pin 33 0.2 Ohms
?Pin 2 -> CPU Pin 61 0.23 Ohms
?Pin 2 -> RP108 Pin 9 0.24 Ohms?
Pin 3 -> U13 Pin 18 0.1 Ohms?
Pin 3 -> Paula Pin 42 0.21 Ohms
?Pin 3 -> Agnus Pin 83 0.13 Ohms?
Pin 3 -> RP109 Pin 9 0.19 Ohms
?Pin 3 -> U19 Pin 1 0.27 Ohms?
Pin 3 -> U23 Pin 1 0.25 Ohms?
Pin 3 -> Denise Pin 40 0.32 Ohms?
Pin 4 -> EvenCIA Pin 32 0.19 Ohms?
Pin 4 -> U13 Pin 5 0.11 Ohms?
Pin 4 -> ROM Pin 17 0.28 Ohms?
Pin 4 -> CPU Pin 60 0.22 Ohms?
Pin 4 -> RP108 Pin 3 0.21 Ohms?
Pin 5 -> U13 Pin 17 0.07 Ohms
?Pin 5 -> Denise Pin 41 0.29 Ohms
Pin 5 -> Paula Pin 43 0.15 Ohms
?Pin 5 -> Agnus Pin 84 0.12 Ohms
?Pin 5 -> RP111 Pin 9 0.15 Ohms
?Pin 5 -> U19 Pin 19 0.24 Ohms
?Pin 5 -> U23 Pin 19 0.24 Ohms
?Pin 6 -> EvenCIA Pin 31 0.17 Ohms
Pin 6 -> U13 Pin 6 0.08? Ohms
Pin 6 -> ROM Pin 19 0.3? Ohms
Pin 6 -> CPU Pin 59 0.21? Ohms
Pin 7 -> U13 Pin 14 0.16? Ohms
Pin 7 -> Paula Pin 44 0.14? Ohms
Pin 7 -> Agnus Pin 1 0.12? Ohms
Pin 7 -> U19 Pin 2 0.23? Ohms
Pin 7 -> U23 Pin 2 0.23? Ohms
Pin 7 -> Denise Pin 42 0.27 Ohms
?Pin 8 -> EvenCIA Pin 30 0.15 Ohms
?Pin 8 -> U13 Pin 9 0.07? Ohms
Pin 8 -> ROM Pin 21 0.17 Ohms
?Pin 8 -> CPU Pin 58 0.23 Ohms
?Pin 9 -> U13 Pin 13 0.08 Ohms
Pin 9 -> Agnus Pin 2 0.15 Ohms
?Pin 9 -> Paula Pin 45 0.18 Ohms
?Pin 9 -> Denise Pin 43 0.3? Ohms
Pin 9 -> U19 Pin 18 0.31 Ohms
?Pin 9 -> U23 Pin 18 0.31? Ohms
Pin 10 -> Ground 0.07 Ohms
Pin 11 -> U13 Pin 12 0.07? Ohms
Pin 11 -> ROM Pin 24 0.22 Ohms
?Pin 11 -> CPU Pin 57 0.20? Ohms
Pin 11 -> EvenCIA Pin 29 0.21 Ohms
?Pin 12 -> U13 Pin 8 0.08? Ohms
Pin 12 -> Agnus Pin 3 0.12 Ohms
?Pin 12 -> U18 Pin 1 0.24? Ohms
Pin 12 -> U22 Pin 1 0.23? Ohms
Pin 12 -> Denise Pin 44 0.26? Ohms
Pin 12 -> Paula Pin 46 0.13? Ohms
Pin 13 -> U13 Pin 15 0.07? Ohms
Pin 13 -> ROM Pin 26 0.33 Ohms
Pin 13 -> CPU Pin 56 0.2? Ohms
Pin 13 -> EvenCIA Pin 28 0.18 Ohms
?Pin 14 -> U13 Pin 7 0.06 Ohms
Pin 14 -> Agnus Pin 4 0.17 Ohms
?Pin 14 -> Paula Pin 47 0.14 Ohms
?Pin 14 -> Denise Pin 45 0.25 Ohms
?Pin 14 -> U18 Pin 19 0.23 Ohms
Pin 14 -> U22 Pin 19 0.2? Ohms
Pin 15 -> U13 Pin 16 0.05? Ohms
Pin 15 -> ROM Pin 28 0.25? Ohms
Pin 15 -> CPU Pin 55 0.2? Ohms
Pin 15 -> EvenCIA Pin 27 0.17? Ohms
Pin 16 -> U13 Pin 4 0.08 Ohms
?Pin 16 -> Agnus Pin 5 0.12? Ohms
Pin 16 -> U18 Pin 2 0.25? Ohms
Pin 16 -> U22 Pin 2 0.23? Ohms
Pin 16 -> Paula Pin 48 0.15? Ohms
Pin 16 -> Denise Pin 46 0.27? Ohms
Pin 17 -> U13 Pin 19 0.09? Ohms
Pin 17 -> ROM Pin 30 0.13 Ohms
?Pin 17 -> CPU Pin 54 0.24? Ohms
Pin 17 -> EvenCIA Pin 26 0.21 Ohms
Pin 18 -> U13 Pin 3 0.06 Ohms
Pin 18 -> Agnus Pin 6 0.12 Ohms
Pin 18 -> U18 Pin 18 0.26 Ohms
?Pin 18 -> U22 Pin 18 0.23 Ohms
Pin 18 -> Paula Pin 1 0.16 Ohms
?Pin 18 -> Denise Pin 47 0.28 Ohms
Pin 19 -> (done with pin 1)?
Pin 20 -> VCC 0.12 Ohms

[DigitalKeeper]

Please check all Traces & VIAs in marked Area's!

Often there are Problem's - renew Solder Blob's!

On Top of the PCB the VIAs (Vertical Interconnect Access) looks like they are ok; on Bottom Side -> the SAME VIA have a failure Signal, or they are broken.



Example:

It's a A600 without "Red" - at this Point -> the Line would be broken at the Pad! Similar to your Amiga -> look ath the VIAs and - i hope so - connected Traces

[solarmon]

@SamBushman

It looks you have put in a lot of effort in checking the traces!

One thing to bear in mind is that sometimes the issue is not that the trace is broken from A to B where it is supposed to go, but because it could also be shorted to C. Thus, your continuity test between A and B will always show continuity between them, but it does not show continuity to C, unless you measure from A to C.

What you could do is to try to measure for any shorts to either ground or VCC. The could be for those traces that have pull down resistors to ground or pull up resistors to VCC.

Since you have DiagROM but your serial output is garbage then I would try to sort that out first - so check around the serial chips. Without output to screen and/or serial, DiagROM is useless. It is common that these serial chips, or components and traces associated with them fail and they need to be repaired/replaced.

[SamBushman]

@DigitalKeeper Thanks for the advice. I just checked the indicated VIAs. All pins and components connected to each VIA appears to connect properly and within the specs I've seen with my other trace checks. At this time I don't believe the VIAs are bad (well, to rephrase I don't think they are the cause of my present symptoms. They quite likely will need a little love to remove the last of the corrosion ).

@solarmon That is a very good point. Checking the various power rails from the DC input port, I find the following:
5V (VCC)
To Ground: 100.7 Ohms
To -12V: No connection
To +12V: No Connection

-12V
To Ground: No Connection
+12V: No Connection

+12V
To Ground: No Connection

Interesting, is that reading between the 5V line and Ground normal?

Also, I absolutely agree with your statement about the DiagRom serial. This was the starting motivation for me checking the various traces on the board. I've traced everything back from the serial port to the custom chips and memory once already. I had found a couple breaks on U12 (which I had replaced with a socket and new IC), but bodging those pins hadn't resolved my issue. I have also already replaced U39 and U38 in case one of theme were to blame. The lack of a smoking gun has been a challenge with getting DiagRom serial to work.

[dalek]

As solarmon aluded to, it looks to me like an address or data line short. Check each address lines for shorts to another, same for each data line.

[solarmon]

Originally Posted by SamBushman

@DigitalKeeper Thanks for the advice. I just checked the indicated VIAs. All pins and components connected to each VIA appears to connect properly and within the specs I've seen with my other trace checks. At this time I don't believe the VIAs are bad (well, to rephrase I don't think they are the cause of my present symptoms. They quite likely will need a little love to remove the last of the corrosion ).

@solarmon That is a very good point. Checking the various power rails from the DC input port, I find the following:
5V (VCC)
To Ground: 100.7 Ohms
To -12V: No connection
To +12V: No Connection

-12V
To Ground: No Connection
+12V: No Connection

+12V
To Ground: No Connection

Interesting, is that reading between the 5V line and Ground normal?

Also, I absolutely agree with your statement about the DiagRom serial. This was the starting motivation for me checking the various traces on the board. I've traced everything back from the serial port to the custom chips and memory once already. I had found a couple breaks on U12 (which I had replaced with a socket and new IC), but bodging those pins hadn't resolved my issue. I have also already replaced U39 and U38 in case one of theme were to blame. The lack of a smoking gun has been a challenge with getting DiagRom serial to work.

I wasn't suggesting that there may be an issue with shorting between the power rails - I think you would know if there was - i.e. components burning!

It was really whether any signal lines were shorted to any of the power lines.

Sorry, I forgot you had mentioned in your first post that you replaced and socketed the serial chips. The serial chips makes use of the 12V and -12V rails, so check that these gets to U38 OK.

The serial traces/signals also go to the CIA's - so you should check the CIA's and possibly swap them to see if that makes a differrence. There are also EMI components on the serial port pins that should be inspected and checked too.

[DigitalKeeper]

For Serial Output -> check Paula and U8 (8520)

As solarmon said - check EMI Filters, coz of short's or broken & Power at U38








Hope it help's a little.....

[SamBushman]

@DigitalKeeper

Hope it help's a little.....

It does. I really appreciate it

@solarmon my apologies. I had misinterpreted your suggestion. I've tested all chip pins against -12V, +12V, Ground, and +5V. All the readings appear to match the Amiga PCB Explorer. I am running with the assumption that by verifying at the chip pins, I won't need to test every via and contact point along the way.

I did see that Paula Pin 34 had 0.14 Ohms to ground. That pin was labeled as "A_GND", so I assume it must be a ground line of some sort.

+12V and -12V lines also appear to connect to U38 ok. Running power through the board, I see the appropriate voltage going across the pins as well.

I have swapped the CIAs before and tested both in a working machine. As far as I can tell, they should be working and all traces have been tested going to them.

Sorry, I forgot you had mentioned in your first post that you replaced and socketed the serial chips.

No problem. I know I've posted a bunch of stuff here already, I'm sure it's easy to miss a detail or two. When in doubt feel free to ask and double check me. I'm happy to validate what's been tested

As for the EMI component, I don't detect any shorts and they seem connected. I don't know how to further test the components. I suppose I could just try replacing them unless there are better suggestions.

One note:
While checking Agnus for shorts I noticed one of the pins (in this case, all my multimeter can reach is the body of the socket pins, not the chip itself) was a little sensitive to actually reading properly (it was pin 41, one of the ground pins). I reflowed all the Agnus pins, but there was no change in behavior

[robinsonb5]

OK, it looks to me like the ROM's reading fine since Kickstart gives you a greenscreen and DiagROM attempts to write to the serial port.

Since both ROMs are apparently hitting the right hardware registers to make the screen flash and serial port emit characters, I think the address lines are probably OK - or at least not the main problem.

Check, double check and triple-check all the traces and vias around U10, U11 and especially U12 and U13, since (a) that's the area of worst damage, (b) you have what looks like a data bus problem, and (c) the data connection between the CPU and chipset / onboard memory goes through there. It's also possible, I suppose, that one of U10/11/12/13 is faulty?

[SamBushman]

Thanks for the suggestions robinsonb5!

An update to my investigation:

I've finished checking U9, U10, U11, U12, and U13. U9 (labeled CLOCK on the board) had 3 different broken traces. I've bodged those. After that fix, all traces on all chips checked out. No pins were shorting with one another, 5V, +12V, -12V, or Ground. With the bodges to U9 there was no change in behavior.

U12 had previously been replaced and socketed due to significant corrosion on the pins. U10 had less, but given how things are going I went ahead and replaced with (adding a socket). No change in behavior.

I could order and replace the other ICs in this cluster I suppose. I have a small bluetooth oscilloscope that I could use to look at some of these pins during operation. However, I'm not really sure what to look for.

Any thoughts on what to try next?

[robinsonb5]

Do you have the facilities to burn your own ROMs?

[SamBushman]

Not currently. Whatcha thinkin'?

[robinsonb5]

Originally Posted by SamBushman

Not currently. Whatcha thinkin'?

Just that since the CPU's own bus seems to be working (since the ROM works), the chipset / RAM bus isn't working and the point where the two join is where the worst of the corrosion happened, it would be useful to be able to put specific signals on the bus using a custom ROM.


Since you have that bluetooth scope, see if you can see activity on the D0 - D4 pins on each of the RAM chips, and also pin 1 of U10, U11, U12 and U13, when you power on...

[SamBushman]

As a slight off topic, I had bought a Pokit Meter a couple weeks ago for this project. I just went to try it tonight and found that it has issues connecting to my android phone. Reading online, many have had that issue. Looks like I gotta explore other options for reading signals off these pins :/

As a lesson to everyone here, the Pokit Meter is not a matured product. I've seen less complaints about iOS but overall I am not impressed. Now back to the Amiga 500+........

[robinsonb5]

Originally Posted by SamBushman

As a slight off topic, I had bought a Pokit Meter a couple weeks ago for this project. I just went to try it tonight and found that it has issues connecting to my android phone. Reading online, many have had that issue. Looks like I gotta explore other options for reading signals off these pins :/

That's annoying. Hopefully you'll be able to find a better solution.


(By far the cheapest diagnostic tool I have is a simple crystal radio earpiece. They're very high impedance so shouldn't affect any logic you probe with them - so much so, in fact, that you don't even need a proper return path! I just tested on my A500+ and I can just about hear some evidence of the signals on the RAM chips' data lines, and pin 1 of U10-13 just by touching the tip of the plug to the relevant pin. If I touch the barrel of the earpiece's plug with my finger at the same time I can hear it more clearly, especially if I allow my hand to touch the RF shielding at the same time. Obviously I can't tell a great deal about what's happening on the pins I'm probing, but I can verify that a signal of some sort is reaching them.)