Issue 6 problems

For experts to discuss very technical stuff and newbies to ask why the Spectrum they bought off ebay doesn't work.
Post Reply
Patxi
Berk
Posts: 7
Joined: Wed Oct 09, 2019 1:29 pm

Issue 6 problems

Post by Patxi » Wed Oct 09, 2019 3:55 pm

Hi!

I am a complete ZX newbie, having recently bought this Issue 6 speccy. I have replaced the keyboard membrane, and i'm waiting for a new cap kit for it and for my M-332.

I ran it today, after replacing the keyboard, and it seemed ok for some 5 to 10 minutes. Then it froze. Powered it down, and the screen would start flickering either showing complete or incomplete Sinclair screen, restarting once or twice a second.

I let it rest for an hour, and then tried it again, this time filming it.

What could this be?



Thank you
0 x

Patxi
Berk
Posts: 7
Joined: Wed Oct 09, 2019 1:29 pm

Re: Issue 6 problems

Post by Patxi » Wed Oct 09, 2019 6:00 pm

Took the multimeter at the 7805.
5.69V input, 4V output.

My working M-332 Speccy pulls the input voltage to the same 5.69V, but somehow keeps on ticking.

Seems like I have a power supply problem, 12+V no load, but bogs down under load.

Image
0 x

User avatar
Mort
Berk
Posts: 40
Joined: Thu Jan 17, 2019 10:03 am
Location: Kent , England
Contact:

Re: Issue 6 problems

Post by Mort » Wed Oct 09, 2019 6:58 pm

If you can`t get a Speccy Psu, pick up the mk1 megadrive psu as this uses the same voltage as the 48k speccy ;)
1 x
Scanner extraordinaire, 1000`s of magazines and Software from the 8 and 16 bit era now up on internet archive in lovely 600dpi.
Donations are welcome of items to scan that are no longer needed ;)

Patxi
Berk
Posts: 7
Joined: Wed Oct 09, 2019 1:29 pm

Re: Issue 6 problems

Post by Patxi » Wed Oct 09, 2019 8:19 pm

Thanks Mort!

I found an online ad for an original 48k PSU for 15€.
Also found a 9v@2A smps for 13€, but needs the plug reworked for polarity.

Do the originals need being recapped?
0 x

User avatar
Ast A. Moore
Dynamite Dan
Posts: 1167
Joined: Mon Nov 13, 2017 3:16 pm

Re: Issue 6 problems

Post by Ast A. Moore » Wed Oct 09, 2019 10:49 pm

Patxi wrote:
Wed Oct 09, 2019 6:00 pm
Took the multimeter at the 7805.
5.69V input, 4V output.
That’s way too low for the 7805. It needs about 7–7.5V minimum to start regulating the voltage reliably. Your PSU is definitely underpowered. Get a good regulated switching PSU that can output 9V at 2A or more. The Spectrum itself normally draws around 600–800 mA, but if you plan to use peripherals with it, it’s good to have some extra power to spare. If you get a 2.5–3A PSU, you can even use it with the 128K/+2 Spectrums as well.

Keep in mind that the Spectrum’s DC-DC circuitry generates all the voltages necessary for the operation of the computer from that single +5V rail provided by the 7805. If they go significantly out of spec, you can potentially damage the lower RAM ICs.
0 x
Every man should plant a tree, build a house, and write a ZX Spectrum game.

Author of A Yankee in Iraq, a 50 fps shoot-’em-up—the first game to utilize the floating bus on the +2A/+3,
and zasm Z80 Assembler syntax highlighter.

User avatar
Ast A. Moore
Dynamite Dan
Posts: 1167
Joined: Mon Nov 13, 2017 3:16 pm

Re: Issue 6 problems

Post by Ast A. Moore » Wed Oct 09, 2019 10:56 pm

Patxi wrote:
Wed Oct 09, 2019 8:19 pm
Thanks Mort!

I found an online ad for an original 48k PSU for 15€.
Also found a 9v@2A smps for 13€, but needs the plug reworked for polarity.

Do the originals need being recapped?
Rarely. The original PSUs are pretty robust. Their biggest downside is because they’re unregulated, the 7805 has to dissipate a lot of extra energy as heat. There are no fans inside the Spectrum, so all that heat pretty much stays inside the computer. This greatly reduces the lifespan of many of its components, so your best bet is a switching PSU. It’s trivial to either open up the PSU and swap the leads for correct polarity, or cut off the original barrel plug that came with the PSU and solder a new one.

Some PSUs are easier to open than others. The could be glued or ultrasonically welded together, or use a few simple plastic latches around the perimeter or even be held together by screws.
0 x
Every man should plant a tree, build a house, and write a ZX Spectrum game.

Author of A Yankee in Iraq, a 50 fps shoot-’em-up—the first game to utilize the floating bus on the +2A/+3,
and zasm Z80 Assembler syntax highlighter.

Patxi
Berk
Posts: 7
Joined: Wed Oct 09, 2019 1:29 pm

Re: Issue 6 problems

Post by Patxi » Thu Oct 10, 2019 10:17 am

New smps, the Speccy is happy!
Image
0 x

User avatar
1024MAK
Manic Miner
Posts: 491
Joined: Wed Nov 15, 2017 2:52 pm
Location: Sunny Somerset in the U.K. in Europe

Re: Issue 6 problems

Post by 1024MAK » Thu Oct 10, 2019 3:28 pm

Patxi wrote:
Wed Oct 09, 2019 6:00 pm
Took the multimeter at the 7805.
5.69V input, 4V output.

My working M-332 Speccy pulls the input voltage to the same 5.69V, but somehow keeps on ticking.

Seems like I have a power supply problem, 12+V no load, but bogs down under load.
The various different issue boards all use a different amount of power. So just because one works with a PSU / mains adapter, does not mean that another ZX Spectrum will work. Sinclair recommended a PSU rated at 1.4A. Although most ZX Spectrums on their own use around 0.8A (800mA).
Patxi wrote:
Wed Oct 09, 2019 8:19 pm
Do the originals need being recapped?
The capacitor(s) used in most have a surprisingly long life. So don’t normally need changing unless you experience problems. If you suspect/ think that there may be a problem, it’s fairly easy to replace the capacitor(s). Normally a single 4700uF capacitor is used. I recommend a new capacitor with a voltage rating of 25V and a temperature rating of 105°C. But check the physical size, as there is not much space in the PSU.

Mark
0 x

Post Reply