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Is there a prime suspect for an Issue 3 board that produces yellow text, instead of white?

Success.

I socketed IC55 and replacing the 4564 did the trick. Cheers guys.

I agree with Kazzie that this is most probably caused by a faulty IC55. Sometimes the first bit (bit 0) is high when it should be low and vice versa. The way it behaves it could well work if you piggyback a working memory chip on it (but you can never really tell). Piggy backing didn't have any eff...

Actually, just a photo of the first (mode 7) screen may be sufficient. Does the sound and the caps lock/shift lock toggling work with Tricky’s rom installed?

Sorry, missed this post. Yes, the sound works at the start and the caps lock/shift lock toggle.

Here's a gif of the start of the test rom but I doubt it's of any help. It is too big to upload here so I've made it available at;

https://www.ictprovision.com:80/pics/TEST2.gif

Ok. On power on with long beeeeeeeep; Pon.jpg After CTRL-BREAK without long beeeeep; ctrl-break.jpg Typing MODE 6; goto-mode6.jpg In MODE6; mode6.jpg and MODE0; mode0.jpg After a memory check, which I assume from previous info means nothing; memchk.jpg Test ROM pic to follow. Hope this helps.

I have a Elk that I _think_ was just waiting for me to fix the internal power pcb. Can't be sure, it's been a while (for while read years), so if you still want one, I can fix the pcb and test the board. It won't be in the next day or two but I will get back to you as soon as I can. Ping me if I don...

Thank you for the comments Kazzie. Firstly (with all the B+-related posts recently I've got them all mixed up in my head) are we talking about a 64k or a 128k model? 64K If you see screen corruption (possibly of a different nature) in other MODEs, then that would suggest that it isn't IC54. Narrowin...

Maybe I should start a new thread on this, if so just say. The reason I asked initially about the B+ memory mapping was that having just sorted my B, due the help received here, I powered up a B+ and got a long beeeeep. Another machine out of the loft. Pressing CTRL BREAK gets rid of the long beeeee...

No. Pin 3 on IC49 which is RD5 is only connected to Din / Dout of IC65. However, I think I understand the point you were trying to make. IC49 pins 2 thru 9 do not translate directly to RD0 thru RD7 as is stated in that other topic. Pin assignment for IC49 is as you have stated. Ok, cool. The owner ...

IC49 is not a RAM chip. It's a 74LS245 tri-state octal bus transceiver. This transceiver buffers the 8 data lines, and each one of these data lines connects to the data in / out pins of each dram chip. Well yes, I know it's not a ram chip, what is confusing me is it's links to the ram chips. From t...

Ok, getting confused now (easily done some might say), Kazzie stated D0= IC55 D1= IC56 D2= IC60 D3= IC61 D4= IC64 D5= IC65 D6= IC66 D7= IC66 and over in the pointed to thread of the B+ ram problem at https://stardot.org.uk/forums/viewtopic.php?t=15961 stated this; Voltmeter measurements on page 1 ga...

Thank you Kazzie for the detailed explanation. every RAM chip is used to provide the byte of memory at every address location So, each memory location, say &3000 for example, comprises of one bit from each dram chip? Therefore, any apparent fault at any location could be caused by any one or more of...

Gah, that's what I get for posting so early in the morning. For a B+, let's try: For a B+ 64k Code: Select all D0= IC55 D1= IC56 D2= IC60 D3= IC61 D4= IC64 D5= IC65 D6= IC66 D7= IC66 The early bird catches the worm :D So, for a mere mortal like myself, how does this equate to memory locations/addre...

Well done
viewtopic.php?f=3&t=6383&p=61457 may help you with your noisy beeb...

Is that topic pertinent to Bs as well as the Master?

Good to see you were successful.

Does anybody know which ram ICs map to which addresses?

Glad to hear that your Beeb's looking more and more healthy! Thank you. With regard to the memory test, memory chips can fail in all sorts of unusual ways, not all of which will be picked up by any particular type-in test. I guess you're right on that. As well as using the likes of Mode 0 to test t...

So, I still have some noise through the speaker. Very faint background noise on key press and a louder hissing noise in tandem with floppy drive usage. Anyway, I ran the memory tester (listing at https://stardot.org.uk/forums/viewtopic.php?f=3&t=14809 ) with and without the LS04 inverter and in both...

I replaced IC32 this morning and had a bit of weirdness then some success. Having replaced the ic, switching on left me in a worse position. I had the continuous beeeeeep and no display. Powered off and then back on, same situation! Did the same for a third time and hey presto, beep, beep and a 16K ...

About the tuneful keypresses: is the tone always the same for each key, and does it differ between keys? Are there groups of keys which give the same tone? I can't see any real pattern other than as well as making a sound of it's own, each key press further distorts the continuous tone that's ongoi...

Could you confirm for me how the Caps and Shift LEDs behave when you turn the machine on, and then after pressing break? Also, is there any difference if you press Control+break instead of break? Sure. On initial power on, no key press response, 'CAPS LOCK', 'SHIFT LOCK' on. On pressing break, no c...

You said pin 8 is now high: that's surprising, as pin 8 should be ground! Did you make an error, perhaps? (Are you sure of the other pin numbers?) Great info, thank you very much. I need to read over it a few times I think, but I just want to correct myself. You were obviously correct about pin 8 a...

Apologies for bombarding you with all this info but it helps me remember what I've done :) Anyway, with a good system, testing IC32 I get; 1->High, 2->High, 3->Low, 4->High, 5->High, 6->High, 7->High, 8->Low, 9->Low, 10->High, 11->Low, 12->High, 13->High, 14->Pulsing, 15->High, 16->High Which is mar...

A little more info. As mentioned, on startup, the keyboard is unresponsive until break is pressed. It was in this condition that the readings with the logic probe in my previous post were taken. If I press break and get a responsive keyboard, the readings change slightly. Here are the differences wi...

The sound chip (IC18, 76489) is connected to the ‘slow bus’ from the system VIA (IC3) and controlled by the /WE signal (pin 5 on IC18). This control signal also comes from IC3, but via IC32 (74LS259). Ok, got IC 33 back in, still the same situation. So, in an attempt to check sound, got my (cheapo)...

Yay!

Some hints and links to guides on using an oscilloscope are here and here

You can either use your logic probe or your ‘scope to trace signals.

Ok, thanks for the info. If tomorrow I get the bits I'm waiting for I'll start having a play with the probe.

By the way, what test gear do you have / have available/ can borrow or pinch?

Well I have a Fluke (179) and a logic probe which I can use confidently, I have a Siglent SDS 1052DL which I'm not so proficient with. In fact, I'm not proficient at all with it, but I would like to be

Default start-up is in MODE 7, the teletext mode. So if there is one or more defective RAM chips, the resulting bit errors will result in the wrong character being displayed. If you know what should be shown (compare to a normal start-up screen), you can use the table of teletext characters in the ...

More info: So, with the inverter fitted I pressed BREAK, typed MODE 6 and typed in the simple memory test prog, as below. Typed characters appear correctly in mode 6. 5 MODE 0 10 ?&4000=0 20 A=?&4000 30 IF A=0 THEN GOTO 20 40 PRINT A This produced nothing but the cursor at the top of the screen. The...

With the inverter fitted the symptoms are similar to those with S25 south. Cannot type until break is pressed . Then th 32k message disappears and typing is possible, albeit with musical tones. The beeeeeeeep continues. Typing in the startup MODE (cant remember what mode that is) produces random cha...