PHP1260 memory expansion issue

[PeteW]

Hello,

 

I purchased a PHP1260 memory expansion card for my PEB.  However when the card is in the PEB and I turn on the PEBand then TI99/4a there is a load constant beep and the screen turns different colors and never comes to the boot screen.  However if I take out the PHP1260 the PEB and TI99/4a will boot normally.  Unfortunately I cannot send it back, so I wanted to know how I can get this fixed.  Does anybody know if there is a reset or anything else I can do to get this fixed?

 

Thank you for your help

[+acadiel]

The actual card itself is simple.  Here's a write up on it:

https://www.unige.ch/medecine/nouspikel/ti99/mem32k.htm

 

Without an oscilloscope, you will need to do trial and error.  I also suggest in seeing while replacing these if socketing the ICs will allow space to keep the clamshell on - that will make it easier to change stuff in the future.

 

The following are components in the card.  The 74LS chips should be easily obtainable.  The 4116/4164s can be obtained by eBay, Unicorn Electronics, etc.  

• 4116 DRAMs (16).  If at fault, these can be replaced by 4164's with modifications or you can use 4116's. @arcadeshopper sells boards that you can use if you don't want to modify each 4164. 
• 3  74LS74   dual-D flip-flop - DRAM refresh
• 1  74LS109  dual JK flip-flop - DRAM refresh
• 1  74LS161  4-bit counter - DRAM refresh
• 1  74LS393  dual 4-bit counter - DRAM refresh
• 4  74LS244  dual 4-bit buffer, 3-state (1 control bus, 2 address bus buffers, 1 DRAM refresh)
• 1  74LS245  data bus buffer 
• A proprietary selection IC (I don't see any further details on the page about it.)
• 2  74LS257 quad 2-to-1 multiplexers - address multiplexers
• 1  74LS123 one shot multivibrator (LED)

You might want to verify the list by looking at the card.  I don't have one handy at present to look at.

 

The first thing I would try would be the buffers (74LS244 & 74LS245).  That has been really the only thing that has ever gone out on me.  The regulators *might* be at fault.  Others can chime in on what to check/try.

 

 

[+Ksarul]

The unidentified selection logic chip is the PAL (U1 on the board), decoded in the PAL/GAL thread. Note that there may be a few chips not identified in the list above on the board as well, as I noticed there is a 74LS125 on it that wasn't identified yet. Here is a set of schematics that may also help. . .pulled from the Mainbyte site (where there are useful schematics, projects, and hardware data aplenty). Note, I haven't done updated A3-size copies of these schematics yet, but that task is on my list.

[+acadiel]

Yep, and I know it might be overwhelming right now - if you don’t know how to solder, feel free to ask for help - I’m sure someone in here can help try and diagnose it.  There’s only so many of these in the wild and it makes sense to try and fix them.  
 

Two more things I just thought of in case anyone else reads this thread in the future:

 

1)  triple check that nobody removed the regulators.  Sometimes, people mod their PEBs to use a PC PSU, and they have to remove the regulators on the cards to get them to work.  These regulatorless cards could be damaged in a regular PEB.  

 

2) Check the 74LS buffer chips on the flex interface card.  I’ve seen most people just replace the ones in the black boot, but have seen others also replace the other side on the actually slot 1 interface card too.  

[+mizapf]

32K RAM: EXP BOX MEU PAL12L6 DEFINITION
RAS0 = MQ2*/A01S + REFRAS*/REFADR7
MESEL = PCBEN*MEMEN*AMC*AMB*AMA*/A01*A02 + PCBEN*MEMEN*AMC*AMB*AMA*A00*A01
RAS1* = MQ2*A01S + REFRAS*REFADR7
AP02 = A00*A02
SPARE OUTPUT
MEMENB = /MEMEN