"8749 replaces 8049" Curiosity

[Harbars]

Hi there!

I recently got another QL, rather ancient and full of all kinds of muck and grime and some dubious mods (a hook up wire not connected to anything floating around inside the case and a failed attempt to solder the LED cables to the connector!).

After a disassemble and a deep clean, basic functions are OK aside the microdrives, which I've not yet attempted to clean up and the left ROM chip, which was fried and needed replaced.
I haven't done any detailed testing, but it boots, shows 128K and can load basic programs from a known good MDV unit from another box. Board is an Issue 5, and the case serial is a D09.

At any rate, the IPC chip has been replaced with what is pictured below, and I was wondering if any one here could shed some light on this.

Handwritten text on the label reads "8749 replaces 8049" and after a brief search here in the forums, it seems the 8749 is an EPROM replacement.
This one also has a mod to it - couple resistors and a transistor. One of the pins is bent so that it doesn't connect to the DIP socket - and was also used to help route the speaker cable.
Two leads just stick up going nowhere, which I guess is OK, but doesn't really sit well with my limited appreciation of basic electronics!

Has anyone seen this before? Would it have been common, and what would the purpose be. Any info on the additional mod also also appreciated.

Cheers
Spence

[Derek_Stewart]

Hi,

This is a Hermes replacement IPC for the 8049 chip in all standard QLs, the components on the chip are the circuit for CAPSLED, see forum thread:
https://www.theqlforum.com/viewtopic.php ... ock#p41027
Which gives the QL a Caps Lock LED and also flashes the LED when the scroll lock is enabled.

I made some 30 years ago like the picture, but it really needs a PCB...

[Harbars]

Marvelous - many thanks for the reply and info. I hadn't considered the Caps Lock LED at all!

Cheers
s.

[vanpeebles]

I love the hacky looking ones

[Dave]

The original maker of the caps lock LED kit is bringing it back, so just hold tight on that one.

[Derek_Stewart]

Hi

I have done a updated PCB, with SMD components, which is 3rd on my list of jobs...

[Harbars]

Could it be possible that the chip is just a "copy" of the original IPC?

After loading the hermes extensions and printing ipcver$ i'm getting back 0.0. Similarly IPCEXT 6 returns "not found" - so it seems the chip isn't a Hermes

[Derek_Stewart]

Hi,

The added components on the chip are to implement the CAPSLOCK_LED circuit, which works with 8049 and 8749.

So from the IPCVER$ function,the IPC is a 8049.

[mk79]

I've never seen a plastic 8749, so I would venture the guess this is a bog standard 8049 as seen in any other QL.

[tofro]

I've never seen a plastic 8749, so I would venture the guess this is a bog standard 8049 as seen in any other QL.

A 8749 would also need to have a visible quartz window (just like an EPROM) to qualify as one - I can't see that in the picture.