48K ZX Spectrum Repair. (No. 6)

[@borayurt66]

It is very normal for a leaky capacitor to show a higher value than it is rated. DMM's measure capacitance by applying a constant current and measuring the charge time. If the capacitor is leaky, some current is lost and the charging time takes longer, thus resulting in a fake high capacitance. Apparently, you have given up on posting videos, so I don't know if you follow comments. I resurrected my old 48K with the great tips I learned here, very good tips derived from experience are present here, I am sure you have many more to share, you should continue.

[@CDOODY1999]

so satisfying to hit on the right component and get one working, I was convinced I had an upper memory problem but I saw your transistor diagnostics and it seamed to fit, took one off my salvage machine and it only bloody worked. I didn't have a lick of experience fixing these before i inherited a box full of my grandads old zx's. thanks for the help.

[@RetroWorkshop]

Excellent video. I’ve just received a Spectrum 48k issue 3 and can now safely check it before powering.

[@GregMcCarthyUK]

Just come across this video. Excellent, love seeing all these retro devices being brought back to life.

[@webwarp2023]

THE BEST SPECTRUM REPAIR VIDEOS ON THE NET

[@mark2097]

After connecting a 9v mains adaptor with the wrong polarity and killing my poor spectrum, you've given me some hope that it's salvageable (maybe!?!) great video.

[@JoulesperCoulomb]

+mark2097 It can be repaired. I'd check the 7805 and the voltage converter circuit first.

[@TheChipmunk2008]

I love that you diagnose what went wrong with the tests rather than just shrugging :-)

[@retrocomputeruser]

At 7:00 The schematic tells you what track goes to what side on all resistors and caps. LT for left and RT for right side. C65 for example is mounted vertically so that has BK & FT.Of course it's always better to check.

[@LFOSyncToo]

Very nice repair and wonderfull video & explanations.

[@EuphoricMonkey]

Another really nice and informative video. Thanks for the effort you put into making it and sharing.

[@Firefoxfifty]

Thank you so much. I was able to repair another zx spectrum with the help of your videos!

[@cbmeeks]

I love these videos. Are you still doing repair videos? Would love to see more.

[@speedsterh]

Top notch repair ! Very very interesting explanations, thanks for sharing a piece of your expertise :)

[@PlasmaHH]

Oh and regarding the pcb repair kits, there are plenty out there, its just that they are darn expensive... just some copper foil and heat resistive epoxy is fine. For the trace you repaired I sometimes like to mill a tiny track into the board and grind one side of a wire flat and insert it with the round side into the groove and fix it with epoxy. looks like an original trace but holds much better. But then again I do that when restaurating pcbs, not when just repairing them

[@Beaps73]

Love learning from you buddy, never doubted you would have it tickin'

[@PlasmaHH]

Regarding diode drop differences in the meters: They are usually implemented as constant current sources, thus the unit likely uses a much lower current. My agilent uses a so low current that it is practically uncomparable, it would like show 500mV for that diode.

[@spudhead169]

Capacitors that have leakage current often measure significantly higher capacitance than their marked value. This is because capacitance testers often use the time it takes for the cap to charge to a particular voltage to determine the capacitance. When the cap is leaking current, it takes longer to charge because some of the current is being lost, thus the meter erroneously reports a higher capacitance.

[@peddersoldchap]

Those ULA chips are not produced anymore, are they? Is there a way to emulate them, for instance, with an EPROM? Also, thank you for the video.

[@michaelhawthorne8696]

Nice vid , well executed fault finding too....

[@GadgetUK164]

Brilliant! Expertly done as usual =)

[@beingatliberty]

amazing job fantastic videos keep up the good works

[@TheBezumax]

is it ok if TR4 NPN shows 0,9 and 0,6 on the N legs? Also on IC pin 1 =0v; pin8=9.4 V. I have changed all caps excluding С46 ,what I should to do next?

[@flyguille]

a q temperatura tienes seteado el desoldador zd916 (creo q es el modelo)?

[@HeyBirt]

The circuit repair kits you were mentioning are made by Pace World Wide. They are not as easy to find these days and not inexpensive for a kit: paceworldwide.com/products/circuit-level-repair/nonthermobond-repair-kits/cirkit-advanced-version-nonthermobond . I'm not sure who might supply them in the UK.

[@networldworld4333]

Hell ! can you help ? i own a zx spectrum sinclair 48k that doesn´t load the games. They just get errors when first game screen opens or crash during the doalings and green little squares on some loading drawings. I inserted that to check the upper RAM chips : PRINT PEEK 23732 + 256 * PEEK 23733 the value result was wrong it was 32863 instead of 6553 »»»» I tested all the 8 upper RAM chips group on the board below (right side not the logical ones) using a fully working sinclair 48k and all 8 are good.

[@jacobartaylor]

I have a possible issue with my spectrum, when i power it up i has a rather annoying high pitched whine noise, do you know if this is normal and if it can be fixed? Thanks

[@JoulesperCoulomb]

What you describe is almost certainly normal, especially if all the power supply voltages are present and correct. It's caused by the windings of the inductor vibrating. It might be possible to reduce it by applying lacquer/varnish/similar to the windings, but take care not to use anything that might attack the wire's insulation or anything else inside the Spectrum.

[@volodimirkun]

Cool, man! Enjoyed lot.

[@PhilReynoldsLondonGeek]

What's the desolderer you use in this video?

[@JoulesperCoulomb]

Mine is branded Duratool and it doesn't appear to have a model printed on it. I've seen it sold under several other names. It seems to be fairly well constructed for its low cost, though the hand piece is less sturdy than I'd like and the rest that attaches to the side of the base unit is very poorly designed and a bit unsafe. As far as de-soldering goes, it works very well so long as it is cleaned out regularly.

[@euphoricmonkey8409]

Really nice video.

[@andygozzo72]

very rare for the coil to fail? oh,yeah!! i've had them go shorted turns and you cant always tell from a resistance test....

[@RichSzerman]

Nice vid.. good work... dont take it personal but don't understand your introduction expression "good time of day to you" .

[@helioshaul3924]

Wonderful Stuff . Thanks.

[@Jenny_Digital]

JoulesperCoulomb Having enjoyed learning more about Spectrum repair from you I thought I'd add that there is a company still doing pcb repair frames in England. I've not bought any from them yet to say how good they are however. www.Intertronics.co.uk