From: Jonno Downes on
I have 3 64cs (one is marked 252311 rev A, another 252311 rev 4, the
third I haven't taken the keyboard off to read the rev markings but
looks to be approximately the same layout as the other 2)

All three are showing the same symptoms, namely when the power on the
led lights up, but the screen stays black. However there is obviously
some sort of video being output because my TV stops saying "no
signal".

For each one, I have powered them on, with a disk drive connected and
tried a few times to type 'load "*",8' to see if any disk activity was
triggered, but none of them do. I then felt every chip on the board -
a few felt a little warm but none where what I'd describe as 'hot'.

Any pointers on how to progress troubleshooting (and maybe even
repair)?

Cheers

Jonno
From: Andreas Meerbann on
On 29 Jun., 12:58, Jonno Downes <jonno...(a)gmail.com> wrote:
> I have 3 64cs (one is marked 252311 rev A, another 252311 rev 4, the
> third I haven't taken the keyboard off to read the rev markings but
> looks to be approximately the same layout as the other 2)
>
> All three are showing the same symptoms, namely when the power on the
> led lights up, but the screen stays black. However there is obviously
> some sort of video being output because my TV stops saying "no
> signal".
>
> For each one, I have powered them on, with a disk drive connected and
> tried a few times to type 'load "*",8' to see if any disk activity was
> triggered, but none of them do. I then felt every chip on the board -
> a few felt a little warm but none where what I'd describe as 'hot'.
>
> Any pointers on how to progress troubleshooting (and maybe even
> repair)?
>
> Cheers
>
> Jonno

well, I'd say the usual method (requires a more or less similar and
working 64)
0a. remove floppy drive connection just to be sure there is no
influence (permanent reset etc)
0b. remove socketed SID chips (the 64 also works fine without!)
1. checking all voltages (the on-board fuse seems OK since video seems
to come out)
2. replacing all socketed chips with known to be good ones from the
working unit (one after the other to see which one was broken)
3. soldering out of the non socketed chips in both working and non-
working unit. Mounting of sockets and then do the same as in step 2

in the given case I'd start with the CIAs, then PLA, CPU, VDC, then
DRAM (a lot to solder!), the 556 reset timer and then finally give up.

have fun :-)

Andreas
From: Clocky on
Jonno Downes wrote:
> I have 3 64cs (one is marked 252311 rev A, another 252311 rev 4, the
> third I haven't taken the keyboard off to read the rev markings but
> looks to be approximately the same layout as the other 2)
>
> All three are showing the same symptoms, namely when the power on the
> led lights up, but the screen stays black. However there is obviously
> some sort of video being output because my TV stops saying "no
> signal".
>
> For each one, I have powered them on, with a disk drive connected and
> tried a few times to type 'load "*",8' to see if any disk activity was
> triggered, but none of them do. I then felt every chip on the board -
> a few felt a little warm but none where what I'd describe as 'hot'.
>
> Any pointers on how to progress troubleshooting (and maybe even
> repair)?
>

DRAM failure is common on this model, the last three I have repaired
recently all had DRAM failure which will result in a black screen. The main
suspect for that would be the power supply, so if you have been using the
same supply for all three C64's I would strongly recommend using another
one.

I'm happy to diagnose and repair the boards if possible for the price of
parts and a little bit of labour, but that would also involve shipping the
boards (cheaper than shipping the whole C64) across the country which might
not be an economical option since I'm in Perth but I thought I would mention
it anyway.




From: Jonno Downes on
On Jun 30, 12:55 am, "Clocky" <notg...(a)happen.com> wrote:
>
> DRAM failure is common on this model, the last three I have repaired
> recently all had DRAM failure which will result in a black screen. The main
> suspect for that would be the power supply, so if you have been using the
> same supply for all three C64's I would strongly recommend using another
> one.
>
> I'm happy to diagnose and repair the boards if possible for the price of
> parts and a little bit of labour, but that would also involve shipping the
> boards (cheaper than shipping the whole C64) across the country which might
> not be an economical option since I'm in Perth but I thought I would mention
> it anyway.

Given that the over the last month, the ebay auctions I've been
watching have ended up with 64cs going for > $100, and breadbins for
over $200, I reckon shipping them may well be economical. Is there an
easy supply of suitable DRAM chips, if so maybe I should try swapping
those first and if that fails, send the boards off to yourself for
some more expert examination? (assuming of course I can't convince you
to come over to the east coast for tinkercon ;-)

I reckon you are right about the power supply, I have 1 remaining
working breadbin, which I am using with a different power supply - the
one time I plugged into the power supply the 64cs were using I got a
crash after 2 minutes, but the one it is on now it has been stable for
hours at a time even when using cartridges like 64NIC+ or IDE64 with a
Compact Flash that I imagine would increase the load on the power
supply.

Regards

Jonno
From: Clocky on
Jonno Downes wrote:
> On Jun 30, 12:55 am, "Clocky" <notg...(a)happen.com> wrote:
>>
>> DRAM failure is common on this model, the last three I have repaired
>> recently all had DRAM failure which will result in a black screen.
>> The main suspect for that would be the power supply, so if you have
>> been using the same supply for all three C64's I would strongly
>> recommend using another one.
>>
>> I'm happy to diagnose and repair the boards if possible for the
>> price of parts and a little bit of labour, but that would also
>> involve shipping the boards (cheaper than shipping the whole C64)
>> across the country which might not be an economical option since I'm
>> in Perth but I thought I would mention it anyway.
>
> Given that the over the last month, the ebay auctions I've been
> watching have ended up with 64cs going for > $100, and breadbins for
> over $200, I reckon shipping them may well be economical. Is there an
> easy supply of suitable DRAM chips, if so maybe I should try swapping
> those first and if that fails, send the boards off to yourself for
> some more expert examination?

They are getting harder to get hold of new though Jameco still sell them but
their minimum order for international customers is $30 plus the postage. I
have a number of spares that I have desoldered and tested, so if you need a
couple for diagnosing I'm happy to pop a couple in the mail for you.

(assuming of course I can't convince you
> to come over to the east coast for tinkercon ;-)
>

I would love to, but I'm currently in no position to travel :-(

> I reckon you are right about the power supply, I have 1 remaining
> working breadbin, which I am using with a different power supply - the
> one time I plugged into the power supply the 64cs were using I got a
> crash after 2 minutes, but the one it is on now it has been stable for
> hours at a time even when using cartridges like 64NIC+ or IDE64 with a
> Compact Flash that I imagine would increase the load on the power
> supply.
>

I wouldn't be using the suspect PSU again. I personally use an ATX supply
alongside a 9V AC 2A transformer from Jaycar with a recycled case and the
power cord salvaged from a dodgey powerbrick. See top picture here
http://users.on.net/~clockmeister/other/VIC20C/