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Old 02 May 2012, 23:33   #1
Retrofan
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Fixing a Spectrum 48k

I'm fixing my Speccy 48k (Issue 2).

I just want to give a couple of good links I've found.

First the screen wasn't right, but (here comes the first link):

http://translate.google.es/translate...2Freparar.html

"Yellow: Set the playing white potentiometers VR1 and VR2 (which only have issue 1 and 2). " ...

Now I've got it perfect.

Second one: It wasn't (still it isn't) loading:
"RAM failure on top. Change a chip 4532 (32Kx1) for 4164 (64Kx1). " -I've read in other place that Spectrum were using half working 64k RAM chips for their upper 32k of memory-

Next step: How do you know which is the ram chip that is out of order?

Link: http://www.worldofspectrum.org/hardware/rep5.html

RAM check procedures
The following routine will isolate a fault at one address of the RAM:
(1) Enter the following: PRINT PEEK 23732 + 256 * PEEK 23733
(2) If the result if other than 65535 or 32767 (16k version) there's a fault.
(3) Add one to the faulty result. Let's say it was 54321.
POKE 54322,85 (Enter) then:
PRINT PEEK 54322 (Enter)
Use your result +1 in place of the example quoted above.
(4) If the answer returned is 85, repeat steps 3 using 170 instead of 85.
(5) One of the answers should differ from the 85 or 170 entered. Provided there is only one faulty ic at the address, Table 2 will indicate which one it is. Find the line with the wrong data bit then refer to IC6-13 if the address is below 32768 or IC15-22 if the address is above 32768.
(6) Repeat step 1 after the repair to ensure that there isn't another fault.

Table 2 : Identifying the faulty chip
-Sorry, open my link, as pasting it you can't read well this part-

Well, I had the result of 93, so I changed IC18 with a chip I had. Unfortunatelly it keeps without loading, and the tests now says 213, so I must change IC22, which I've just ordered (well, a couple of them) http://www.ebay.es/itm/310095483722?...84.m1439.l2649. I'm mounting every chip I change on sockets.

At least I've found a good way to know where the problem is

Last edited by Retrofan; 12 May 2012 at 03:31. Reason: Thread moved.
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Old 10 May 2012, 18:35   #2
bugsthor
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i got a fault 48k which ive been looking at fixing, i`ve done a fix to make the RF put out vga, but no picture , i think my ULA is dead , but spare RAM chips , got a 48k in a box on its way working and another one for spares . found those fixes the other day.
but thanks for posting links.
they are prity hard to find these days, so maybe an idea to give or copy URL/s , or info we find, i wanted to make a web page with stuff i find on the old 48k as it would be getting more rare from now on me thinks. there are some old spectrum magazines on ebay going for sale atm, looking in rity good condition, after being stuck in a loft for 20yrs. i`m concidering geting them and scanning those babies, like HOL and EAB.

hanks again for the easy REF/s
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Old 11 May 2012, 01:26   #3
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i gtot one of them today. lots of goodies

but this old problem
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Old 11 May 2012, 09:42   #4
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this could help someone

found what could be my problem.

http://www.tablix.org/~avian/blog/ar...th_experience/
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Old 11 May 2012, 23:56   #5
Retrofan
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Quote:
Originally Posted by bugsthor View Post
i gtot one of them today. lots of goodies

but this old problem
Your's seem http://translate.google.es/translate...2Freparar.html a Z80 problem. Make the ram test too http://www.worldofspectrum.org/hardware/rep5.html. (Edit: Oh, sorry, you can't, so just try with the Z80).

"The Spectrum is based on a Zilog Z80A CPU running at 3.5 MHz (or NEC D780C-1 clone). " http://en.wikipedia.org/wiki/ZX_Spectrum

I think this: http://www.ebay.es/itm/CPU-ST-Z80ADA...item35bbc57c92
Btw: I've changed my keyboard, membrane and the printed kb metal frame, so I've got my Speccy as new. If you need them surely I can find where I got them.

Last edited by Retrofan; 12 May 2012 at 03:14.
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Old 12 May 2012, 22:46   #6
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hey Retrofan thanks for the links, its the same one i found

a little bit of soldering i think, got two with picture problems, so i think i`ll use my 1st one and take the Z80 from that one, and swap and jiggle the lower memory chips around to see if i could possibly fix the two from the scrap yard which would be kind of ACE.

my keyboard check would have to come after the Z80 swap/testing. there could obviously be more errors yet to find

but the mebrains look prity good , and the outside of both is in mint near new condition for their age , with only two rubber feet missing off one

i`ll get them out and take some picture/s for you and anyone else, and some details of my fixes with pics.
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Old 12 May 2012, 22:53   #7
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Be careful while desoldering. The traces like to go up when you try to lift the chip... If you don't desolder all completely (and it's hard to do) you'll find that you'll have to repair that traces. Perhaps a hot air gun would make it easier. What about the printed kb metal frame? It likes to lose paint...

Edit: Yes, weekend, but I've got to fix the Spectrum (I've received the ram chips), close the BPPC Amiga taking and uploading photos, install (or create) all in a new A1200, try a new 8mb ram in my Hawk ramboard, retrobrightning and all, opening the other A1200 to try the sockets for the fast ata and the Mk2 Indi (unopened parcel, let's see tomorrow)... add the home work for the weekend... and I think I have a baby and a wife somewhere in the house.... Lol

Last edited by Retrofan; 16 May 2012 at 23:15.
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Old 13 May 2012, 13:00   #8
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Ok, I don't know what chip ram I must change.
I've changed IC22 and now making the test:
PRINT PEEK 23732 + 256 * PEEK 23733

I've got a result of 32775. The thing is that after making
POKE 32776,85 (Enter) then:
PRINT PEEK 32776 (Enter)
I've got a result of 85. Making
POKE 32776,170 (Enter) then:
PRINT PEEK 32776 (Enter)
I've got a result of 170.

So, I don't know what is the faulty chip.

It seems I'll have to start changing them one by one.





Last edited by Retrofan; 13 May 2012 at 14:56.
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Old 13 May 2012, 20:51   #9
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few more links i found, could come in handy for people.

and easy REF:- to save other people and us time, spent 2 days with hardly any sleep finding some of these better links. so mainy dead page

will update Links with INFO/s to save even more of your time.
might get myself a website to save what left of these infos. as you never know when they are going to disapear from the web (email the owners 1st show some respect)

http://8bit.yarek.pl/computer/zx.48/index.html

http://user.tninet.se/~vjz762w/

http://tarjan.uw.hu/zxclones_en.htm

http://womblesretrorepairshack.blogspot.co.uk/

something about spectrum child (will read through it, and edit this for clarity)
http://www.dotkam.com/2008/11/19/zx-spectrum-child/

Retro treasures blog
http://retro-treasures.blogspot.co.u...-warranty.html

some fixes with pictures common errors for spectrum
http://retro-treasures.blogspot.co.u...-warranty.html

google search IMAGES PRON
https://www.google.co.uk/search?hl=e...w.r_qf.,cf.osb
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Old 14 May 2012, 16:44   #10
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well changig ram on zx spectrum can be a pain retro fan is right i destroy one board trying to get the chip too fast and the traces come together and other bu cutting with a dremel went down til it cuted the traces underneath the chip, although i found this way best if you got steady hands i used to remove my mc68000 on the amiga then cleaned the rest of the solder and pins,i have an timex that also when loading a game passes program then get me the message ram top no good ,i think is a faulty ram too ,but finding the bad (faulty ram)seed is another story
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Old 14 May 2012, 21:37   #11
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found this for yo if its any help Retrofan

Table 1 : RAM check procedures

The following routine will isolate a fault at one address of the RAM:

(1) Enter the following: PRINT PEEK 23732 + 256 * PEEK 23733

(2) If the result if other than 65535 or 32767 (16k version) there's a fault.

(3) Add one to the faulty result. Let's say it was 54321.

POKE 54322,85 (Enter) then:

PRINT PEEK 54322 (Enter)

Use your result +1 in place of the example quoted above.

(4) If the answer returned is 85, repeat steps 3 using 170 instead of 85.

(5) One of the answers should differ from the 85 or 170 entered. Provided there is only one faulty ic at the address, Table 2 will indicate which one it is. Find the line with the wrong data bit then refer to IC6-13 if the address is below 32768 or IC15-22 if the address is above 32768.

(6) Repeat step 1 after the repair to ensure that there isn't another fault.

link to page:-
http://members.multimania.co.uk/eigh...pair/rep4.html
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Old 14 May 2012, 21:46   #12
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Thanks a lot, but you haven't read my links and post 1. That info is what I'm using in another link. The thing is that after having changed 2 chips now having a first result of 32775 later I get results 85 and 170, so what?

Edit: Another thing that I didn't comment (yes, it's for rom, not ram, but...). This test:

ROM Check

The program given below will enable you to verify that the ROM is satisfactory.

10 LET 1=0
20 FOR n=28003 TO 28033
30 READ a
40 LET 1=1+a
50 POKE n,a
60 NEXT n
70 DATA 17,0,64,62,0,33,0,0,1,0,0,134,48,2,3,63,35,29,32,247,21,32,244,50,96,108,237,67,109,201
80 IF 1=2033 THEN GO TO 110
90 PRINT "Error in Data"
100 STOP
110 RANDOMIZE USR 28003
120 PRINT PEEK 28000 +256 * PEEK 28001 + 65536 * PEEK 28002
180 STOP

The first line is wrong. The Spectrum doesn't let you write that and it has no sense. Changing 1 for a letter, later I had an Out of data message.

Last edited by Retrofan; 14 May 2012 at 21:54.
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Old 15 May 2012, 21:43   #13
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even if you get any error on pokes it is some times dificult to trace the chip in some models and error could be also no power or cut line in some IC.
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Old 23 May 2012, 04:53   #14
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how the repairing bugsthor the best way is like i said cut with ease the pin legs with a dremmel not touching the pcb ,remove the rest of the pins by unsoldering one by one much more easy and apply ram chip sockets in case in the future you need to replace again the spanish web page refers those white and black bars for damaged ic 18 ,but i think that depends on the model you have, my timex boots ok,but when loading says ramtop no good when i replace the ram i am going to put sockets too ,it is not original but much more pratical on repairing and no one is looking inside
keep in thouch
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Old 24 May 2012, 02:04   #15
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not yet rampartsagain,

cannot find where i seen the link for those sockets, would have got them by now, but been side tracked with life this past week to do any work on them.

what i did find though is my second soldering iron, which i need to file down the end so it`ll make my life easier to solder /de-solder the stuff. where pcb are concerned my tool box is vertually empty, i need to get some small snips to do what you say.
no vault tester/ no clips for removing chips from sockets(i use a small screw drive)
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Old 24 May 2012, 02:21   #16
Retrofan
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Quote:
Originally Posted by rampartsagain View Post
how the repairing bugsthor the best way is like i said cut with ease the pin legs with a dremmel not touching the pcb ,remove the rest of the pins by unsoldering one by one much more easy and apply ram chip sockets in case in the future you need to replace again

That's fine if you've got a lot of chips to replace them, but my plan is to go testing one by one, and to keep the working ones on sockets.
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Old 24 May 2012, 02:38   #17
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got a link to i can get the sockets to fit
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Old 24 May 2012, 03:03   #18
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bugsthor you can see under ebay i don´t remembr how many pins 4116 ram chips have but on ebay you put like 12 pin socket and there you go,i hope there should be an easy way to test maybe you can check like when error message occurs try to measure each voltage pin of the ics and try to see if any is like be grounded were the voltage drops ,if you know what i mean
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Old 24 May 2012, 04:14   #19
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just got me a old new Z80 woohoo cheep as chips pardon the pun lol.

ok i`ll try that search now rampartsagain.
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Old 24 May 2012, 04:23   #20
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that is excellent i am a fan and collector of amigas and spectrum and the things i love most is when i bought the are dirt and tired ,after opening and washing all the plastics cleaning the pcb,blow on the air compressor then silicone protection assemble all and see the old machines gaining life i feel on top of the world
like a zensation
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