Search found 455 matches

by tcat
Sun Apr 08, 2018 2:22 pm
Forum: Hardware
Topic: All RAM chips destroyed??
Replies: 62
Views: 4986

Re: All RAM chips destroyed??

Hi Martyn, those JUx represent wire-links/zero-ohm resistors on the Iss-5 boards...They appear immediately between the ZX8302 and the right-hand ROM socket. ql-iss#5.jpg In the picture above I only located JU1,2,6 in the red rectangle, but manual refers to JU2,3,4. Is it just me looking at the wrong...
by tcat
Sun Apr 08, 2018 11:11 am
Forum: Hardware
Topic: All RAM chips destroyed??
Replies: 62
Views: 4986

Re: All RAM chips destroyed??

Hi, I have been following this topic with a great interest, while learning a lot about QL as well. It made me read several chapters from the service manual again, now with slightly more understanding. The chapter on firmware upgrade caught my attention. 4. Remove IC17 (74LS00). 5. Remove IC33 and IC...
by tcat
Thu Mar 15, 2018 6:00 pm
Forum: Hardware
Topic: Microdrive boards
Replies: 26
Views: 2096

Re: Microdrive boards

Dave wrote:Unfortunately, the company that made the heads went out of business a long time ago.


Ah bad luck, many thanks anyway.
Tomas
by tcat
Thu Mar 15, 2018 1:54 pm
Forum: Hardware
Topic: Microdrive boards
Replies: 26
Views: 2096

Re: Microdrive boards

I can get the combo ERP heads from a specialty company Hi Dave, I am so currious about R/W head drop in replacement, as I thought it impossible. Slightly off-topic, while I was looking for an audio device with continuous loop, I came accross STEREO-8 system. Developed by Lear Jet aircraft company. ...
by tcat
Wed Mar 07, 2018 5:24 pm
Forum: Hardware
Topic: 74HCxx vs 74LSxx
Replies: 5
Views: 543

Re: 74HCxx vs 74LSxx

Hi PrOf,

Perfect, the document even mentions some macro definitions, that could help to provide FPU library. 74HCxx are used to drive chip select, would it fail to function with 74LSxx?

CIRCUIT.PNG
FPU-CPU peripheral wiring
CIRCUIT.PNG (8.54 KiB) Viewed 476 times

Many thanks.

Tomas
by tcat
Wed Mar 07, 2018 11:33 am
Forum: Hardware
Topic: 74HCxx vs 74LSxx
Replies: 5
Views: 543

74HCxx vs 74LSxx

Hi, I plan to build a simple FPU board for MC68000, based on a DIY design. I need to decode many address lines. Am I safe to replace original 74HCxx chips with 74LSxx ones, as these seem easier to get here? I cannot tell any difference between LS and MC technology, and when to use one or the other. ...
by tcat
Sat Dec 09, 2017 1:40 pm
Forum: Hardware
Topic: The Mandatory Modifications
Replies: 6
Views: 861

Re: The Mandatory Modifications

Hi Cristian,

Just observations, need to be proved by experience of others.

I reckon you have Iss#5 QL board to service, I wish to learn from your steps, if you shared here in the forum, I may do the same in parallel.

Tomas
by tcat
Fri Dec 08, 2017 10:26 am
Forum: Hardware
Topic: ZX Interface I - under the hood
Replies: 5
Views: 499

Re: ZX Interface I - under the hood

Hi Charles, Your post was quicker than mine. I see Q11 transistor. My Speccy is Iss#3 so perhaps a later model. I was confused when looking at ULA pin1 (with a dot) and its opposite pin 40 ~ with +5V VCC, this is where one transistor leg is fitted through a wire? Compared to the diagram, annotated b...
by tcat
Fri Dec 08, 2017 9:27 am
Forum: Hardware
Topic: ZX Interface I - under the hood
Replies: 5
Views: 499

Re: ZX Interface I - under the hood

Hi Prof,

Thank you. I have assembled it again. But it seems middle transistor leg (possibly its base), is attached to ULA pin 10? Perhaps service manual has some info, that I do not get. I have only a circuit diagram inside the manual of poorer quality.

Tomas
by tcat
Fri Dec 08, 2017 8:55 am
Forum: Hardware
Topic: ZX Interface I - under the hood
Replies: 5
Views: 499

ZX Interface I - under the hood

Hi, I would have normally posted to `World Of Spectrum' forum, but I got SSL handshake failed, so I hope may get some attention here as well. I have recently recapped my Speccy also I1, now looking inside it, I would like to know the function of a transistor flying on top of ULA. Please see picture....

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