75D First Steps.

[dhe]

I received the 75D I purchased from the bay.

1) It's very very dirty, but doesn't appear to have had major damage.
2) I'm guessing first steps are to buy a charger and batteries.
3) It appears to me the AT&T Docking Station is screwed in to the unit, I didn't see any sort of 'quick release' buttons.
4) I did open the docking stations battery compartment, while there was no batteries, it didn't appear any batteries, went bad locked in the compartment.

I'm hoping the more knowledgeable can point me to the correct charger and batteries.

I will upload some quick pics next.

Thanks,
Dan

[dhe]

Did I mention it was dirty?

[Dave Frederickson]

I highly recommend you get some of Mark Hoskins AAA battery adapters. See the Parts and Services article. Then get some good LSD NiMH batteries like Eneloops or EBL's (now back in stock at Amazon) and charge them in a smart charger, like a BC-700.

For an AC adapter, the 82059D is what you need.

The 75 separates from the POD by loosening the six large screws on the bottom of the POD.

For getting the gunk out of the keyboard, I've been using Cyber Clean.

Be extremely careful if you ever need to disassemble the 75. The mounting posts get brittle and easily crack when removing the screws.

Find an I/O ROM as Sylvain suggested and maybe a memory module.

Dave

[dhe]

Ok..

I think I have a 82059D. Do you know if it's safe to test this power adapter without being under load - ie.. plugged in and CAREFULLY putting two meter probes to either end?

My normal mode for cleaning old calc's has been to spray a bit of deox on a lint free qtip and clean power terminals.

For the outside case, moisten a lint free q-tip with multi-surface cleaner and gentle go over the case. No pressure on my q-tip, no batteries and waiting a day for everything to dry. << Does that sound reasonable?

I've order some batteries from the bay, I'll clean while I wait for them to come in. I'm also going to hand wash the AT&T case!

I appreciate all the advice.

[Dave Frederickson]

There's no problem plugging in the adapter without a load. I measure 12.8 VAC on mine. The output should be about 8 VAC under load.

All of your other methods sound good.

[Sylvain Cote]

Hello Dan,
If you intent to remove the 75 from the POD, look for a 2.5mm jack connector at the back of the POD.
If you have one it mean that the 75 internal audio wires has been bridged to the POD.
It also mean that you will have to open up the 75 and unsolder these wires.
I have 5 or 6 PODs and half of them had the wires.
Sylvain

[rprosperi]

How does your 75D reply to the MEM command, it will be either 16K or 24K (if 8K RAM module is installed). Most 75D on PODs have the 8KB RAM module installed, so it's likely yours does too. The POD has RAM but it's RAM disk only, so you cans store data and program files, but it can't be used as system RAM.

If it is 24K then...

The good news is YAY, you have 24KB, the maximum system RAM a 75 can have installed.

The bad news is Booo, you have 24KB, the maximum system RAM a 75 can have installed.

Also, how does it reply to VER$, which will show the OS ROM versions. Known values are aaaaaa, bbbbbb, or dddddd.

[dhe]

Hi Bob,
I need to get a set of batteries and see if it even powers on, but as I progress, I'll do this as a serial of my adventure. I'm somewhat hopefully the bottom of the POD says 64K. Next week will be exterior cleaning while I wait for the batteries.
I really do love reading the serial adventures of repair found on this forum and the camaraderie of the help and encouragement people get!

To take a slight turn....
I read the article on LSI and the making of the 75's CPU, learned me something.
I also used to subscribe to byte and creative computing and electronics magazine as well as popular mechanic. Those where good times.

[dhe]

So last week, whilst waiting for batteries to come in, I gave the machine a good cleaning. Remember this was an ebay as is sale on the 75D.

Batteries came in, dropped them in place, and ...

Wait, what? Where's the on and off key?

Downloaded the manual, ah... on is attention.

While holding breath, hit the ATTN button, unit powered on, asked me for the time and date! W00T!

All keys seem to work, LED is crisp and sharp with no missing pixels and basic program ran to completion. I'd say I got lucky.

Now to check out memory and any optional ROM's that might be hiding.

[rprosperi]

(04-21-2021 07:25 PM)dhe Wrote:  So last week, whilst waiting for batteries to come in, I gave the machine a good cleaning. Remember this was an ebay as is sale on the 75D.

Batteries came in, dropped them in place, and ...

Wait, what? Where's the on and off key?

Downloaded the manual, ah... on is attention.

While holding breath, hit the ATTN button, unit powered on, asked me for the time and date! W00T!

All keys seem to work, LED is crisp and sharp with no missing pixels and basic program ran to completion. I'd say I got lucky.

Now to check out memory and any optional ROM's that might be hiding.

Congratulations on a good deal! You can't win if you don't play...

By hidden optional ROMs, are you suggesting some ROMs may be installed inside? Though likely possible from a h/w perspective, and despite being fairly common for 41C and 71B machines back in the day, I don't recall this being done with the 75C/75D. No doubt that was partly due to the very high cost for these machines, but I'm also not sure if 4+ ROMs could be installed (logically) at the same time.

@anyone - is this feasible and do you recall this being done?

[Sylvain Cote]

(04-21-2021 09:06 PM)rprosperi Wrote:  I don't recall this being done with the 75C/75D. No doubt that was partly due to the very high cost for these machines, but I'm also not sure if 4+ ROMs could be installed (logically) at the same time.
@anyone - is this feasible and do you recall this being done?

memory space allocation
IVT: 0 to 17B (9 ISR using 2 bytes each)
ROM: 18B to 24K
ROM: 24K to 32K bank switched system & front port ROM (maximum 18 banks or 6 banks per front port slot)
RAM: 32K to 56K
ROM: 56K to 64K-256
I/O: 64K-256 to 64K

All 8KB of all the banks of all plugin ROMs are located at the same address space (24k to 32K)

[Paul Berger (Canada)]

(04-21-2021 09:06 PM)rprosperi Wrote:  

(04-21-2021 07:25 PM)dhe Wrote:  So last week, whilst waiting for batteries to come in, I gave the machine a good cleaning. Remember this was an ebay as is sale on the 75D.

Batteries came in, dropped them in place, and ...

Wait, what? Where's the on and off key?

Downloaded the manual, ah... on is attention.

While holding breath, hit the ATTN button, unit powered on, asked me for the time and date! W00T!

All keys seem to work, LED is crisp and sharp with no missing pixels and basic program ran to completion. I'd say I got lucky.

Now to check out memory and any optional ROM's that might be hiding.

Congratulations on a good deal! You can't win if you don't play...

By hidden optional ROMs, are you suggesting some ROMs may be installed inside? Though likely possible from a h/w perspective, and despite being fairly common for 41C and 71B machines back in the day, I don't recall this being done with the 75C/75D. No doubt that was partly due to the very high cost for these machines, but I'm also not sure if 4+ ROMs could be installed (logically) at the same time.

@anyone - is this feasible and do you recall this being done?

I don't think it would be feasible there is very little empty space inside a 75, but there would be room inside a pod, especially if you chucked the 300 baud modem, in fact I have toyed with the idea of a PMS like device inside a pod. I have built a read only ROM emulator but it still needs work, I will have to get back to that one of these days. My ultimate goal would be an expanded PMS like device that uses nonvolatile memory like FRAM.

Paul.

[rprosperi]

(04-21-2021 11:10 PM)Paul Berger (Canada) Wrote:  

(04-21-2021 09:06 PM)rprosperi Wrote:  Congratulations on a good deal! You can't win if you don't play...

By hidden optional ROMs, are you suggesting some ROMs may be installed inside? Though likely possible from a h/w perspective, and despite being fairly common for 41C and 71B machines back in the day, I don't recall this being done with the 75C/75D. No doubt that was partly due to the very high cost for these machines, but I'm also not sure if 4+ ROMs could be installed (logically) at the same time.

@anyone - is this feasible and do you recall this being done?

I don't think it would be feasible there is very little empty space inside a 75, but there would be room inside a pod, especially if you chucked the 300 baud modem, in fact I have toyed with the idea of a PMS like device inside a pod. I have built a read only ROM emulator but it still needs work, I will have to get back to that one of these days. My ultimate goal would be an expanded PMS like device that uses nonvolatile memory like FRAM.

Paul.

Thanks Paul. I have a Pod ready to lose its modem when you're ready...

[dhe]

The way the att pod fits, it only shows two rom ports, I was thinking att probably had proprietary software in one of the other slots?

Any mine reports:
MEM - 22423
VER$ - bbbbbb

I'm also assuming to upgrade I just need to copy the correct file onto a USB thumb drive and boot from it? =)

[Paul Berger (Canada)]

(04-22-2021 08:53 PM)dhe Wrote:  The way the att pod fits, it only shows two rom ports, I was thinking att probably had proprietary software in one of the other slots?

Any mine reports:
MEM - 22423
VER$ - bbbbbb

I'm also assuming to upgrade I just need to copy the correct file onto a USB thumb drive and boot from it? =)

While it is not quite that simple unfortunately, it would be possible to replace the system ROMs there is a pin on one of the ROM ports that disables the system ROMs. During development of the 75 the operating system ROMs where on an external EPROM board. I have one of these EPROM boards and it does not appear that they used this signal line, as that signal line is not connected. I also have a prototype card set for a 75 and the system ROMs are not populated on it.

Paul.

[Dave Frederickson]

(04-22-2021 08:53 PM)dhe Wrote:  The way the att pod fits, it only shows two rom ports, I was thinking att probably had proprietary software in one of the other slots?

Any mine reports:
MEM - 22423
VER$ - bbbbbb

I'm also assuming to upgrade I just need to copy the correct file onto a USB thumb drive and boot from it? =)

The Pod connects to the 75 via the right-most front port. See the Pod manual.
http://www.hpmuseum.net/document.php?hwfile=6200

The firmware could be upgraded with a FRAM75, like FRAM71 can do with the 71B, as soon as someone makes one.

Dave

[dhe]

Thanks, that document answer all the questions I had about the POD.