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Old 5th Jan 2021, 8:00 pm   #1
Malcolm G6ANZ
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Default Editing VHS

Following advice on here I set to and changed a lot of caps on the video cards. The majority that I changed were 47uF and were probably decoupling for supply rails. I also changed all the smaller value ones, 2.2uF 10uF and similar. Changing these seemed to make more difference than the decoupling ones. I first tried to get the E-E working so i could see a decent set of colour bars on the output. The bars were just visible but very noisy with no sync, after changing the decoupling caps with no major improvement I started on the smaller ones Each time I changed a few I powered the machine to see what, if any, difference had been made. After changing one of the smaller value caps I was rewarded with a set of locked bars, although still noisy. After changing a few more of the small value caps I had perfect colour bars.
When playing a tape the picture was locked but noisy. Again I swopped out caps and tested after several were changed. Again after one swop I was rewarded with a decent picture.
There are still more 47uF caps to change but I have runout and waiting for delivery.
The photos show the number of caps I have changed and the noisy bars.
So far I haven't tried to record on the machine but it does look hopeful.
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Old 5th Jan 2021, 8:25 pm   #2
HamishBoxer
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Default Re: Editing VHS

Excellent job and result. I can see why you have run out of 47uF,s!!
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Old 6th Jan 2021, 1:41 pm   #3
Welsh Anorak
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Default Re: Editing VHS

As a matter of interest, what method do you use for removing these? Everyone seems to have their own!
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Old 6th Jan 2021, 3:25 pm   #4
Malcolm G6ANZ
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Default Re: Editing VHS

When I started on the marathon cap change I tried to remove each cap bwithout damaging them. I did this by using solder braid and then carefully lifting the legs off the PCB. This was difficult as the legs were under a plastic mounting plate so there was a problem in getting the pad hot enough without melting the plastic. After a few abortive attempts I went for brute force and just twisted and pulled each cap until the body came away from the legs. I could then remove the plastic plate and desolder the legs from the pads. This left a nice clean pad to solder in the new caps. The caps usually came out easily sometimes both legs came out of the body and sometimes only one and the other lifted from the solder pad. There were only two cases when the action of pulling tore the track from the board, luckily in both cases it was to the -ve pad so by scraping off the varnish coating I could find and reuse the remaining track.
The twist and pull seems brutal but it works and in many cases the caps were packed so tightly together desoldering them would have been impossible.
The photo shows the dismembered cap, legs and plastic plate with a 5p coin for scale.
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Old 6th Jan 2021, 3:33 pm   #5
Nickthedentist
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Default Re: Editing VHS

Thanks for letting us know how you did it, and well done! I'm glad it worked after all that hard work.
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Old 6th Jan 2021, 3:44 pm   #6
Malcolm G6ANZ
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Default Re: Editing VHS

There's still more caps to change purely as a precautionary measure. But the system is happy now. I just hope the heads are OK for a while to come.
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Old 6th Jan 2021, 7:17 pm   #7
Ted Kendall
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Default Re: Editing VHS

I find twisting can cause print damage, particularly if the cap has leaked. I use a pair of cutters on the can to get most of it off - the plastic plate can then be picked off and the legs removed, Trouble then is tinning the pads - the fishy goo forms a near-impermeable crust.
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