A500 wavy screen

Misko78 · 10 December 2021, 00:17

Well i bought one 4.5A power supply really cheap. One of the capacitors was leaky so I've recaped it before connecting it to Amiga. Checked the voltages after the recap and it was +5.2V +11.89V and -11.80V. Connected the Amiga and i have wavy lines on the screen that almost disappear when floppy is running. Voltages measured on floppy connector under load are 5,03V and 12,0V. Games work fine. What can make this issue? With Meanwell RT-65B and 2,5A heavy brick there are no waves on the screen.

Power supply is the same as Jan Beta reviewed here [ Show youtube player ]

whaka · 14 December 2021, 17:15

did you replace some capacitors with ultra low esr ? (specially thoses at output ?)
in some cases, very low esr is problematic for regulation feedback and can lead to weird behaviour.

Misko78 · 14 December 2021, 22:43

Just used the regular 105°C ones from local electronics store.

I fixed it. Resistor in position R2 were in fact two 330K Ohm resistors in serial connection, at first i thought it was a Commodores fine work but when i looked at the high res pictures of the same power supply i found that two had 1M Ohm resistor and one had 820K Ohm resistor in position R2. So i called my engineer friend for and advice and he told me that it could make mess, and to swap it out for a 1M one. Everything works perfect now and maybe i?m just imagining runs a little bill cooler.

Misko78 · 16 February 2022, 12:17

Unfortunately, when i connected HC508 accelerator waves appeared again, also tried it on A1200 with TF1230. When any Amiga is accelerated it has waves, without it the screen is crisp and clear.

Misko78 · 03 March 2022, 21:12

In the end problem was with the box X2 capacitors. Both of those were in the spec when measured with capacitometer but I've changed them anyway and voila no interference at all.

pandy71 · 04 March 2022, 15:47

Quote:

Originally Posted by Misko78

In the end problem was with the box X2 capacitors. Both of those were in the spec when measured with capacitometer but I've changed them anyway and voila no interference at all.

Capacity is one side and ESR is also important - older caps may have poor ESR (too high to efficiently reduce current ripple).

10 December 2021, 00:17	#1
Misko78 Registered User Join Date: Sep 2021 Location: Belgrade, Serbia Age: 46 Posts: 32	A500 wavy screen Well i bought one 4.5A power supply really cheap. One of the capacitors was leaky so I've recaped it before connecting it to Amiga. Checked the voltages after the recap and it was +5.2V +11.89V and -11.80V. Connected the Amiga and i have wavy lines on the screen that almost disappear when floppy is running. Voltages measured on floppy connector under load are 5,03V and 12,0V. Games work fine. What can make this issue? With Meanwell RT-65B and 2,5A heavy brick there are no waves on the screen. Power supply is the same as Jan Beta reviewed here [ Show youtube player ]

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14 December 2021, 17:15	#2
whaka Registered User Join Date: Jan 2017 Location: France Posts: 102	did you replace some capacitors with ultra low esr ? (specially thoses at output ?) in some cases, very low esr is problematic for regulation feedback and can lead to weird behaviour.

14 December 2021, 22:43	#3
Misko78 Registered User Join Date: Sep 2021 Location: Belgrade, Serbia Age: 46 Posts: 32	Just used the regular 105°C ones from local electronics store. I fixed it. Resistor in position R2 were in fact two 330K Ohm resistors in serial connection, at first i thought it was a Commodores fine work but when i looked at the high res pictures of the same power supply i found that two had 1M Ohm resistor and one had 820K Ohm resistor in position R2. So i called my engineer friend for and advice and he told me that it could make mess, and to swap it out for a 1M one. Everything works perfect now and maybe i?m just imagining runs a little bill cooler.

16 February 2022, 12:17	#4
Misko78 Registered User Join Date: Sep 2021 Location: Belgrade, Serbia Age: 46 Posts: 32	Unfortunately, when i connected HC508 accelerator waves appeared again, also tried it on A1200 with TF1230. When any Amiga is accelerated it has waves, without it the screen is crisp and clear.

03 March 2022, 21:12	#5
Misko78 Registered User Join Date: Sep 2021 Location: Belgrade, Serbia Age: 46 Posts: 32	In the end problem was with the box X2 capacitors. Both of those were in the spec when measured with capacitometer but I've changed them anyway and voila no interference at all.

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