Electronic repair question C64

jvdbossc

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I have one C64 that is making (over the RF modulator) a chopper sound, continuous, interchanged SID chip, less chopper, but still there, no caps broken to be spot in eye-sight :( Unit working fine for the rest, could sell it when repaired instead of loosing one piece of history ..

The R/F modulator is doing nice work for the rest, looks sharper & better then most units.

I have a nice fluke multimeter, but don't know how to messure the caps to be quite honest.

What should I messure (resistor value? caps keeping voltage? ) Have no clue..:oops:
 

TheCorfiot

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Using your multimeter, check the +12V supply at Pin 28 & +5V supply at Pin 25 of the SID (6581) chip.

Have you tried the Audio out of the A/V socket, is the Audio clean or still "choppy"

FYI

The SID 6581 was first used in the Commodore 64. It is a synthesizer with many synthesis controls and filters; additionally, it has two builtin A/D converters (used for the paddles and analog mice in the C-64). It needs both 5V (Vcc) and 12V (Vdd) supply voltage, the latter generated from the 9VAC delivered by the power supply by using a rectifier bridge with a 12V voltage regulator after it.
With the new boards (C64G and late flat case-C64s), Commodore introduced a new version of the VIC and the SID. The new SID 8580 only needs 5V (Vcc) and 9V (Vdd) for operation.


TC :)
 

jvdbossc

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Thanks, did not think of that :Doh: If it's a small "coppor small psu" problem, probably will keep the unit myself, and solder a molex connector to it. Will let you know that it was that..
 

jvdbossc

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It's alway's nice with some word of advice to have a go at these problems. :)

I must admid I blew the fuse when mesuring, but it was not on the SID where I ****ed up it was somewhere else, luckily:)

The fuse blowing could be quite a photographic thing to do, might have a go if I can find them cheap enoug:p

I started to mesure between GND and any PIN number it mesures mostly 4.85 and one pin (there two indications on the chip one how to put the chip in and one I think where the nummering starts (I think will post pic)

Not pin 1 but the first pin in next row gets 12 volts. Strange thing is this unit has 7805 AND 78012 in it, and it delvers perfectly:help:(eh did deliver before I put my mesure pin between the 7805 (luckily before)
 

Merlin

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@ Jurgen

If you need a spare fuse, I can take the one out of my spare 64 board that TC has already had the SID chip from; do you want it?
 

jvdbossc

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No thanks Merlin, I have 6 dead ones, and I know a shop in front of my door, not electronics, but they do have them for years :)

---------- Post added at 20:36 ---------- Previous post was at 20:33 ----------

Here is the beast, did not find a coil convertor, but hey adding a molex (at psu)after the 780X is easy enough, if they would be to blame.



---------- Post added at 20:38 ---------- Previous post was at 20:36 ----------

If you look at the sid chip, it has two spots, one indicating to position the chip , one I THINK to start counting, now the first pin from the other row has 12 V on it, most all others have 4.8, (messured between GND and pin..)

---------- Post added at 20:43 ---------- Previous post was at 20:38 ----------

I add on that the 780X delivered very close to there specs, about 0.03 voltage off according to my fluke at most!!
 

TheCorfiot

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Follow this linky ;)

http://ist.uwaterloo.ca/~schepers/MJK/sid.html

The notch on the one end of the chip helps identify Pin 1. Some chips also have a dot engraved on the housing next to pin 1 too.

Chip pin numbering then continues anti-clockwise. so you can identify Pin 25 & Pin 28 easily.

All DIL - Dual In Line IC's are numbered in the same manner.

Hope this helps fella
TC :)
 

jvdbossc

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Thanks, so this means:

PIN 28 has got 12 Volts (like it should have)

I read already some of the pages, It's quite interesting, it learnes me the resistor color code value's to messure.. Next check will be pin 14 (GND reducing interference) AND other psu unit, I think I'll just solder the molex from an AT psu :Dto the 780X x2 , I will look for haircracks on all units to.

I will look for the proper hook up cable to. (for composyte connector and audio)

Do I need to remove the 780X if I feed the right legs +5 and +12 , or do they act like a DIODE? (meaning having resistor function in them, while I provide the right current on there legs where they put out the stabelised current? (no need to desolder them or cut them..)


it would mean two things, me not selling it, me finishing up on a project started..:unsure: Commercial value is zero, for 10 eu after all, I could think of other types of projects to have some extra cash.:roll: But hey personal value is always worth more then money..
 

dabone

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There are 2 sources of +5v in the c64.

One is the power supply, this is the one going to the cpu, cia, ram, etc.
If you have no +5 on pin 40 of the cpu, check your power switch.
(Just replaced one last night).

The other source is a 7805 that powers the vic II and related circuit.
It takes its input from the 9v ac input.

The power switch uses the inner 4 pins, the 2 towards the back are the 5v and the other 2 the 9v ac.


Later,
dabone
 

jvdbossc

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Continue

Continue

I was planning to abandon this, but I bought a jiffydos - autoboot rom that needs this type of mobo.:(

So first question:

Where to find this type of rom socket? 24 pins?



I am busy with the caps to, to eliminate the chopper sound.

I desoldered the biggest ones just while at it ..

 

jvdbossc

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@Merlin

Thanks for those links I learned that they translated socket to a local dutch word in the local electronic shop, meaning I needed to translate the word socket.

http://www1.conrad.be/scripts/wgate/zcop_be3/~flNlc3Npb249UDkwX0JFX0IyQzpDX0FHQVRFMDU6MDAwMC4wMGQxLjk5YTBjMGVkJn5odHRwX2NvbnRlbnRfY2hhcnNldD1pc28tODg1OS0xJn5TdGF0ZT0yMDcwMDcxNzI=?~template=PCAT_AREA_S_BROWSE&mfhelp=&p_selected_area=%24ROOT&p_selected_area_fh=&perform_special_action=&glb_user_js=Y&shop=BE&vgl_artikel_in_index=&product_show_id=&p_page_to_display=DirektSearch&~cookies=1&zhmmh_lfo=&zhmmh_area_kz=&s_haupt_kategorie=&p_searchstring=IC+FITTING+24&p_searchstring_artnr=&p_searchstring_manufac_artnr=&p_search_category=alle&fh_directcall=&r3_matn=&insert_kz=&gvlon=&area_s_url=&brand=&amount=&new_item_quantity=&area_url=&direkt_aufriss_area=&p_countdown=&p_80=&p_80_category=&p_80_article=&p_next_template_after_login=&mindestbestellwert=&login=&password=&bpemail=&bpid=&url=&show_wk=&use_search=3&p_back_template=&template=&kat_save=&updatestr=&vgl_artikel_in_vgl=&titel=&darsteller=&regisseur=&anbieter=&genre=&fsk=&jahr=&jahr2=&dvd_error=X&dvd_empty_error=X&dvd_year_error=&call_dvd=&kna_news=&p_status_scenario=&documentselector=&aktiv=&gewinnspiel=&p_load_area=$ROOT&p_artikelbilder_mode=&p_sortopt=&page=&p_catalog_max_results=20
 

TheCorfiot

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Turned pin strips are always handy to have, I used some tonight to create a 40 Pin DIL socket to replace a Z80A & repair a ZX Spectrum.

You could use the same to create the socket you need.

TC :)
 

jvdbossc

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Tc,

I saw "the strips" somewhere, I'll have to find the translation.

Boss is away, so I'll have a local drive to electronic store.

I would like to desolder most IC's so it would be easy to "repair" it in the future. It would be a good practice for me, since my solder skills are uumm..

Thanks guys(y)
 

TheCorfiot

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Well here's a good tip for you, as I used tonight to remove the dead Z80A, it really does save damage to the PCB pads & tracks.

Using very fine nosed cutters, cut each leg of the IC as it exits the Ceramic body of the chip.

Then remove Chip body, you will be left with legs sticking out of the PCB.

Using a fairly fine soldering iron on the top (IC) side of the board apply heat where the bottom of the leg touches the solder pad.
When the solder fully melts & the leg moves use tweezers & pull the leg clear..

When all legs have been removed. use Chem-Wick desolder braid to clear the holes.

Deflux the now clear solder pads with IPA.

Solder in the turned pin strips..


Job done (y)

TC :)
 

jay

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Don't blow that 6581R4AR!
I've been trying to find a good R4AR for years. Just can't find them anywhere. I gave up buying C64's on the off chance that I'd find an R4AR and buying c128's is just too expensive.
The one I have is from a guy off ebay, but the filter is slightly distorted.
So, keep yours un-broken :p
 

arnljot

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@jay

I had to edit your post. I'm sorry, but there is no commenting on pricing my friend.
 
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