DRAM 128K system has stopped working

[MbeeTech]

Hi Chesh.
Just thought I would mention, there is always the option of sending it in for repair.

[ChickenMan]

A GQ-4x4 Eprom Programmer will read and burn all varieties of Microbee EPROMs from 2716 to 27128 as well as 2532's, including 12v and 25v varieties. I have one of these and works from Windows XP to Windows 11.  I can always burn you out an EPROM, just PM me what your after or grab one of these off eBay - GQ-4X v4 USB Programmer Eprom Chip Burner GQ-4X4 BIOS Flash PIC AVR SPI I2C | eBay

All the BN54 eproms are "proper", the bn54_2732 doesnt have the Networking part, the bn5442 was the original issue while bn5443 has updated Networking (43) code.  Most found in the wild labelled as bn54 are the bn5443 variety.

[CheshireNoir]

Cheers Ewan.
At this point I might just have to take you up on your offer. I'll persevere for a bit longer as I'm learning a heap of stuff.
Cheers ChickenMan.
Thank you a heap for clarifying the difference between the BN54 ROMs. I was quite confused by the different file names. That ROM burner definitely looks interesting. I have a local guy who can burn me pretty much any ROM in the short term. (He's part of the Arcade repair fraternity, so has every adapter for every ROM in existence as pretty much every variant was used in an arcade board sooner or later)

As always, you're all super helpful! It keeps me pushing through the pain barrier.

Chesh

[someone]

Someone has no short term memory & is easily confused & prone to errors.

[CheshireNoir]

You and me both, someone.
I rely on tiny post-it notes and LOTS of cross referencing what I have already posted, and even then I get things wrong...
Well, the work week is over, which means I can get the 'bee back on the bench :-)
Ewan, I have replaced C46. No change.
I'm getting some 27128 ROMs blanked so I can try some ROM images.
Interestingly I dropped back in the RAM test ROM and I'm now seeing it fail at random locations while doing the RANDOM NUMBER test, somewhat, err, randomly. Certainly at different addresses each time.
I've also been monitoring the power rails and seeing a bit of fluctuation. Nothing I'd call terrible. probably ±0.2V but it comes and goes. The voltages will be stable, then they'll flicker, then they'll go stable again.

I have a bunch of 1/2 watt TRACO 7805 replacements. I could drop them in instead of the 2 regulators on the core board, assuming the core board doesn't pull more than half a watt per regulator.

I'll update the post once I've tried a BN54 ROM and a combined BASIC ROM. (I think Ernest suggested both of those)

Cheers, and always, thanks for your help.

Chesh

Ps. If I cant get things working by the end of this week I'll pack it up for Ewan to look at. I know when I have reached my skill limits. There's also the matter of the 3 different Amigas I have recently received that also need attention :-D

[CheshireNoir]

OK Folks,
I broke out the ROM Programmer, and then dug out my collection of 27128 ROMs left over from upgrading the PC85b back in the day. (The very same main board underneath the new DRAM core board I'm playing with now. The Core board is set aside for now. I'll probably look at upgrading the Personal Communicator with it if I can get this DRAM Core board working reliably)

What I have tried:
BN5443 - No change. Still doesn't seem to boot.
BN55 - I checksummed it and the ROM itself is fine
BASICA+B - It boots into basic fine! The keyboard works and I can type my "Hello World" 2 line BASIC program in.
(The BASICA+B is just microbee-pc85-eprom-a.bin and microbee-pc85-eprom-b.bin burned sequentially onto a 27C128)

What does it all mean??

BTW I also tried pulling the FDC controller chip in case it was a bad chip, but there's no change. Tired it with both the BN5443 and BN55 ROM.

The scope is on the bench, and I can get the risers out at the drop of a hat if need be :-)

Chesh

[MbeeTech]

Are you changing anything on the motherboard between swapping in the ROM coreboard and the DRAM coreboard?
There are track cuts and links to be done. The Baseboard in a ROM bee situation generates a signal when memory is accessed at F000h->FFFFh
but when set up for a DRAM based bee, the DRAM coreboard generates this (because of the bank switching arrangement for DRAM banks and switching
video ram in and out.

Have a look at the Hardware notebook and see the notes on upgrading to a Computer in a Book from a ROM based bee.

[CheshireNoir]

Hi Ewan,
Yes, when I did my initial attempt I didn't realise the main board needed the mods. Once I realised I dug out the Hardware Notebook (I now have a printout as I keep referring to it) and converted it. It worked fine for about a week then stopped (Just before I was due to take it to a local retro meet, no less)
I also converted it back to test if the main board had failed or the core board. (It worked fine with the PC85 core board)
I then converted it again back to DRAM for the ongoing testing. This time I did it a lot neater too. :-)

BTW, if it's causing confusion, the BASICA+B ROM is sitting in the DRAM core board. A suggestion from Ernest.

Cheers!

Chesh
(Who has just voted early to avoid the rush)

[Ernest]

Interestingly I dropped back in the RAM test ROM and I'm now seeing it fail at random locations while doing the RANDOM NUMBER test, somewhat, err, randomly. Certainly at different addresses each time.

Interesting that you are now having random problems with the TEST ROM memory test. Do the random failure happen on one particular bank or pair of banks or across all banks?
Quite probable that you have some contact issues either with the 2x 25 way headers between the Main and Core boards or even your IC Sockets, have good look at you EPROM socket. The original ones were not meant for multiple insertion removals and can be a bit of a problem. Are your RAM chips socketed?
The fact that BASIC fired up OK is a good sign, as this takes out a number of variables, bank switching and FDC being two main ones.

When you are saying that the neither the BN5443 nor the BN55 are booting up, earlier you described it as "doesn't even get a video sync" is this still the case or can you get into the Monitor with the BN5443 by powering up with the M key held down? If it is trying to boot the floppy through the FDC, you should get a block cursor at the top left of the screen until the floppy starts to boot, however depending on your setup may end up being off the top of the screen if your monitor is over scanning.
Depending on if you can get into the monitor or not will tell us if it is a floppy disk booting issue or a more sinister hardware problem with the Coreboard.
I don't have a BN55 EPROM to see if we can do the same there, but I would expect so.
The best I can tell is the BN5443 is meant for the 5.25" ds40 drives and the BN55 was for the 3.5" ss80 drives. It is possible that the routines for the ds40 access may have been replaced by those for the ss80, but I'm only guessing on this.
I assume you are using a GOTEK for Floppy Emulation?

Ernest

[CheshireNoir]

Can I just start with a huge "Thank you!" to everyone for so much help.
Seriously, this is really heartening. keeps me going on this one.

Interesting that you are now having random problems with the TEST ROM memory test. Do the random failure happen on one particular bank or pair of banks or across all banks?

Seems to be across multiple banks. I've seen it on bank 0, 1 and 2 so far.

Quite probable that you have some contact issues either with the 2x 25 way headers between the Main and Core boards or even your IC Sockets, have good look at you EPROM socket. The original ones were not meant for multiple insertion removals and can be a bit of a problem. Are your RAM chips socketed?

I've cleaned the edge connectors with a very mild abrasive (ink eraser) and deoxit. I have reflowed all the pins on the core board edge connector. The socket for the ROM is a turned pin socket so should be good for a LOT of reinsertions.  The RAM is not socketed but I can socket it if need be.

The fact that BASIC fired up OK is a good sign, as this takes out a number of variables, bank switching and FDC being two main ones.

I'll take the progress where I can get it :-)

When you are saying that the neither the BN5443 nor the BN55 are booting up, earlier you described it as "doesn't even get a video sync" is this still the case or can you get into the Monitor with the BN5443 by powering up with the M key held down? If it is trying to boot the floppy through the FDC, you should get a block cursor at the top left of the screen until the floppy starts to boot, however depending on your setup may end up being off the top of the screen if your monitor is over scanning.

OK I did some extensive testing. When it doesn't work, I literally get "No Signal" come up on screen.
I have tried with both the BN5443 and the BN55 ROM. Both on startup give "No Signal" regardless of whether the M key is held down or not, and regardless of whether the Floppy Drive Controller Chip is in. Permutations FTW! No black cursor. I'd recognise that from when it was working. Pressing the reset key a bunch of times (in all permutations) usually gets a screen full of squares and symbols (Usually capital I characters) . Pressing the reset key a bunch of times with M held down usually gets a black screen. No cursor. This has changed along the way (M used to get me a Monitor screen but no keyboard. Whatever got the RAM test starting seems to have stopped the monitor starting). Most of the time pressing the reset key does nothing. Note this is only with the BN54 and 55 ROM. It works fine for Memory test. I haven't checked with BASICA+B

Depending on if you can get into the monitor or not will tell us if it is a floppy disk booting issue or a more sinister hardware problem with the Coreboard.
I don't have a BN55 EPROM to see if we can do the same there, but I would expect so.
The best I can tell is the BN5443 is meant for the 5.25" ds40 drives and the BN55 was for the 3.5" ss80 drives. It is possible that the routines for the ds40 access may have been replaced by those for the ss80, but I'm only guessing on this.

Hmm. I can't get into monitor at all any more, which points to something more sinister. I can run my TL866II+ over all the logic chips that are socketed, and now my desoldering station has a new gun, desoldering is a heck of a lot easier. I am happy to desolder chips as needed if you want to give me a short list.

I assume you are using a GOTEK for Floppy Emulation?

Yes, but as it isn't getting to the cursor screen, I haven't been plugging it in.

Ernest

Thanks again for all the help!

Hope these symptoms mean something to someone. I also have some photos of the screen if anyone thinks they'll help? Scope is on the bench, ready to go.

Cheers!

Chesh