Spectrum 48k - Issue 2 - Repairing

[Bubu]

Oh, my godness!!! [mention]1024MAK[/mention], thanx a loooot!!!! Really this is not an answer, it's actually a book, I'm going to print it and bind it, wwaaawwww!!!

Then first 'm gonna do is to replace TR4, but not soldering strightly a new one, but through a.. a.... I don't know the name... errr.... this:

[Bubu]

And here's the result:

Implementing a socket for TR4:




Here we are, TR4 and TR5 are in each socket:






Then, powering up!!!




And writting BORDER 1 (by shorting KB1 and KB2 with a cable, LOL):




The result, perfect color, and very clean image:






YEEEAAAAHHHH!!!!!

Now I need to test if there's 16KB or 48KB RAM, I'm afraid it's 16KB, but I've got no keyboard for typing... I'm going to borrow to another speccy

[1024MAK]

Oh, my godness!!! @1024MAK, thanx a loooot!!!! Really this is not an answer, it's actually a book, I'm going to print it and bind it, wwaaawwww!!!

Okay, but I’m not colouring in the pictures (even if I have a qualification in art).

Then first 'm gonna do is to replace TR4, but not soldering strightly a new one, but through a.. a.... I don't know the name... errr.... this:

0.1 inch socket strip…

Or 2.54mm if you prefer metric

YEEEAAAAHHHH!!!!!

Now I need to test if there's 16KB or 48KB RAM, I'm afraid it's 16KB, but I've got no keyboard for typing... I'm going to borrow to another speccy

Well done!

Now doesn’t that feeeeeel goooood

Mark

[Bubu]

Yessssssssssssssss!!!!!!!!!!!!! And this PCB has almost everything in sockets

Let's go with next issue: the upper RAM fault. I've just plugged a DivIDE and tried to play a 48K game, but it crashes at first or 2nd second, so I'm pretty sure I have no upper RAM at all. And I have no keyboard by now. Do you know if I can use the DivIDE to make some test?

Meanwhile, I see some chips that I still don't understand what the are for: 1 x 7400, 4 x 74157, 1 x 7432. If they are useful for addressing the upper RAM, then maybe my RAM chips are OK but some of these LS aren't. I'm going to study !!!!!!!!!!

[Bubu]

*** FIXED !!! ***







I cant believe what the fail was... I had 4164 chips for upper RAM but... had forgoten to cut the pin #1 !!!! I thought it didn't mind as every pin #1 was 0V (GND), but not, they MUST be cutted.



Now I'll find a keyboard for this Issue 2, and finish yeahhhh!!!

[Bubu]

Summing up :

- VIDEO (12V) FAIL:
- 7805 replaced by Traco Power
- TR4 replaced by ZTX651 (and socket)
- TR5 replaced by BC557 (and socket)

- UPPER RAM FAIL:
- 8 x 4164 cutting pin #1

[Bubu]

Nothing is easy... I've borrowed a keyboard to try this PCB, and it doesn't close, it looks as if the Traco is too large for the Speccy to close.

[patters]

I believe for the Issue 2 the Traco needs to be mounted on its side, with additional bits of wire rising up to make the connections to its pins. Retroleum sells a Murata regulator which mounts sideways for this specific use case. See bottom of this page.

Nice work on the repair. I like reading this kind of thread as the person inches closer and closer to success ultimately

[Bubu]

Thank you, [mention]patters[/mention]!

Ok, I'll desolder the Traco, solder 2 thin legs to it, so I can overthrow the Traco. My worry is that Traco's legs are veeery fragile..

[patters]

[mention]1024MAK[/mention] posted this image over at Sinclairzxworld of a sideways regulator installation on a ZX81 which shows a good way to do it - by winding the wire around the legs so that the solder at that joint doesn't break as you heat the part that's being soldered to the PCB. For the wire, use some offcuts from resistors.

[Bubu]

Very good idea, and I tried it but for me it was some difficult to handle with those so small offcuts... I thought of this idea:





I mean, put a... a... socket strip (thanks, [mention]1024MAK[/mention]) and bend it.

[Bubu]

FINISHED

Here some pics of the final result:









THANK YOU, SPECTRUMCOMPUTING!

[spider]

Only just seen this but "well done!"

[1024MAK]

Only just seen this but "well done!"

Absolutely

The wire I used for mounting the RECOM was more likely off-cuts of telecom solid core 0.9mm or 0.63mm diameter copper wire. Fixed telephone or network cable would do.

I use a set of very fine (small electronic size) round nose pliers to put the coiled bit on the end.

Mark

[]-[]

It looks like all the DRAM was originally soldered. And all the original DRAM has been removed. The ‘lower’ DRAM chips been replaced with 64K bit DRAM chips that only need a single +5V supply. That may explain the changes near to capacitor C44.

Has the +12V supply to pin 8 of the ‘lower’ DRAM been isolated from the +12V supply? And instead been connected to the +5V supply?
Has the -5V supply to pin 1 of the ‘lower’ DRAM been isolated from the -5V supply?

It looks like the ‘upper’ DRAM chips are now 64K bit DRAM chips as well.

The Z80A looks like it’s been changed as well.

Mark

Hi Mark,

I have a poorly 48k Spectrum Issue 4B, it seems like a lower ram issue, I'm just waiting for some BAT85 diodes so I can do the OR gate mod. I intend to try the DiagRom written to a 27128 chip to verify this is the case. Doing the resistance check between pins 1 & 16 comes in at about 2.7kR across all of them so it doesn't look good. I have available to me some quite a number of MB8118-10 ram chips and also HM4864P-2. Would either of these be OK as replacements if the board is modded to provide only +5v to pin 8?

Thanks H

[1024MAK]

@]-[ I suggest you start a new topic. Having multiple repairs in the same topic often leads to confusion.

Mark