Broken ZXpander

Discussions about Sinclair ZX80 and ZX81 Hardware
sirmorris
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Re: Broken ZXpander

Post by sirmorris »

Are you well practised in desoldering?

There are a couple of best practises I can suggest if you're not used to this kind of thing.

C
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questarian
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Re: Broken ZXpander

Post by questarian »

sirmorris wrote:Are you well practised in desoldering?

There are a couple of best practises I can suggest if you're not used to this kind of thing.

C
Thanks, any suggestions would be greatly appreciated! I've done some, so I've got desolder tape and an iron with a suction tip. I usually use a clipper to cut the leeds close to the bad chip then desolder each pin... if there's enough leed left, sometimes I've put a clip on it for for a gravity assist. I've had better luck with older stuff and it seems like the melting temperatures on the new solders is somewhat higher and the tape I have isn't wicking as well as it used to.

-John-
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Andy Rea
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Re: Broken ZXpander

Post by Andy Rea »

nothing wrong with cutting the pins and then removing them 1 by 1, it's what i do if I'm certain the chip is scrap, extra solder flux may help your De-solder tape (braid) to wick a little better.

Andy
what's that Smell.... smells like fresh flux and solder fumes...
sirmorris
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Re: Broken ZXpander

Post by sirmorris »

Great, I think you're on to a winner with that technique. There's nothing unusual about the board apart from the close proximity to the eprom socket so you should be fine if you go steady.

Keep us informed!

C
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questarian
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Re: Broken ZXpander

Post by questarian »

Well no good news I'm afraid. I replaced the RAM and no change, it still won't start up... :(
sirmorris
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Re: Broken ZXpander

Post by sirmorris »

.. and you've tried swapping the PIC/GALs over. Have you switched chips since replacing the RAM?

Have you checked the voltages coming from the regulators? The large tab is V-out, and looking at the device with the three smaller tabs at the bottom from left to right you have GND, V-OUT, V-IN.

Was the SD card in the slot during testing? It's possible to bake cards - I did so once but it's pretty unlikely I'd say.

The rest of the components are unlikely to fail though it is possible to kill diodes and resistors but the effect of that would be pretty noticeable...

I suspect we're looking at a return-to-base for diagnosis. I'll be happy to investigate - all you'll need to do is arrange shipping.

C
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questarian
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Re: Broken ZXpander

Post by questarian »

I've swapped the chips between the two of them several times, with and without the SD, I've looked cold solder joints and bridges.... I'm reluctant to do more swapping as I've bent pins a number of times and I expect that if I do much more they'll begin breaking off.

I ran a meter on the regulators briefly before I left for work and I got 3.26v on the one , if memory serves, under the SD and 4.97v on the other.

I gave it a lot of thought last night, and at this point, all things considered, between the postage, repair , time and burnt fingers... had forgotten the RAM was sitting between the ROM socket pins and a fairly tight fit... I'm thinking it may be better to just writing it off as experience, buying a replacement, and using the bad one for spares.

-John-
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PokeMon
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Re: Broken ZXpander

Post by PokeMon »

questarian wrote:and burnt fingers...
Welcome in da club. :mrgreen:

Last week I tried to repair an RTC circuit DS1287 with my mini drill and finally the motherboard of my compaq 286slt (laptop) come only up with error 102 (I think the 162 or 163 before showing low battery was quite better). :roll:

Image
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questarian
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Re: Broken ZXpander - It Lives!

Post by questarian »

When My new hardware arrived today I decided to swap out the v6.6 ROM from my DOA board with the V6 on the working board I had so that my two working ZXpanders would both be running the same new versions... but when I swapped the ROM, the second one stopped working!!!!! For a moment I really thought I was cursed. For laughs I put the other v6 ROM in the "DOA" ZXpander and it started working again!!!

It appears that the ROM was the problem all the time. I would have sworn I tried swapping them between the two several times, and I'm sure the second one never flinched once. I'm going to check the socket on the "DOA" ZXpander and the pins on the ROM. So now I guess I need to get a new ROM... and once I get it going again, can anyone point me at a RAM test program to check the memory I replaced? :)

PS: Sorry it's a bit off topic but out of curiosity...On the ZXpander-AY, should all the pins on the audio out jack be soldered? on the new one I got they are, but on the first I received the inner two, of the row of four, are not.

-John-
sirmorris
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Re: Broken ZXpander

Post by sirmorris »

Hi - great news!

Well, these things happen - even now. I've done it a few times myself. It's very easy to lose track of what has been swapped with what, and end up with a bad prognosis :D You never know - it may have been a combo of ROM and RAM that was damaged.

Do you have EPROM programming facility? I'm away from my programmer for a little while so sending a new EPROM out will have to wait a few days. Rich may be able to come up with a solution though.

The only pins to make contact on the audio socket are the outer 2, sometimes I solder the inner pair, sometimes not. I think it depends on the weather :lol:

Glad it's working.

C
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