Commodore monitor 1084S-P and PHILIPS CM8833II

[demonlg]

Thx Bennehboy.....1901 is my dream but is not possible to buy one with a onest pricing!

In fact.....i have another monitor to check and eventually repair, an old but good condition 1701 commodore monitor, but not powered on from many years, about 10... but this is very rare and this time i disassemble and clear all part before powering on, and then repair if necessary... i open another post when try with it.

 

[demonlg]

Ok i have found the audio problem, i have missed to reconnect a black ground wire from audio section to the main ground, now is perfect, closed and completed.

Thanks at all

Emanuel

 

[daver2]

Woop, woop...

Dave

 

[spiny]

Hi all,

I found this thread on google, and its literally the only one i can find with actual info on how to fix the CM8833 I have one that has a similar fault to a few in this thread, so I'm going to bump this rather than create a new one.

Mine has an odd issue where the screen 'bounces' after it warms up. powering off and back on does not clear the 'bounce'

example vid:

i have replaced all the caps except the 4.7up 50v BP one, as i ordered 47uf by mistake, so the proper one is in the post, but the issue is still there.

I then replaced the D1577 with a BU205BA , which is apparently the current best practice ? but when I turn it on after that, i get the -exact- same issue as demonlg on page 2, literally so exactly the same theres no point me making a vid

thankfully, when i put the D1577 back in place, the monitor powers up normally, but still has the bounce.

original (heatsink is only temporarily removed, it'll get refitted) :



replacement I used, which didn't work:



soooooooooooo, am i on the right track replacing the D1577 for the issue I have, or should i be looking somewhere else.
I have the 'hot' as well, but i'm sensibly for a change, just replacing one thing at a time so I can troubleshoot this properly



cheers, Phil.

 

[demonlg]

I have used BU508AF or S2000 to replace 2SD1577, the BU205 is not goot for me, or is defective because the video on first post indicate a short circuit, but i think so the problem you have is not this transistor the cause, normally when are defectiv the monitor won't start EAT high voltage in horizontal circuitry or if short the same problem of video in post2.

For me is a problem in vertical section.

 

[daver2]

The strange thing is, the 'pulsing' appears to be every second. Is this correct?

Have you checked the vertical drive / synchronisation signal to the monitor for stability before replacing anything else?

Dave

 

[spiny]

I have used BU508AF or S2000 to replace 2SD1577, the BU205 is not goot for me, or is defective because the video on first post indicate a short circuit, but i think so the problem you have is not this transistor the cause, normally when are defectiv the monitor won't start EAT high voltage in horizontal circuitry or if short the same problem of video in post2.

For me is a problem in vertical section.

thanks I'll try a BU508AF, just in case

 

[spiny]

The strange thing is, the 'pulsing' appears to be every second. Is this correct?

Have you checked the vertical drive / synchronisation signal to the monitor for stability before replacing anything else?

Dave

I have tried several different Ataris and my 1200, all do the same thing, though it's not instant, if the monitor is cold, the picture is rock solid and looks amazing, but after about 5 minutes, it starts to 'pulse', slowly at first, then speeds up gradually, then after about ten mins it settles at the speed you can see in my video clip.

It's like something is breaking down when it warms up

but i don't know what :D

 

[daver2]

OK, thanks. I'll take a look at the schematics.

I am going to look for a power supply capacitor feeding the vertical dive circuitry.

If it is temperature dependent (of course) I would recommend a can of freezer spray and a hair dryer to find the faulty component.

Do you have an oscilloscope by the way?

Dave

 

[demonlg]

Just for info, i have verified the BU2508A and the specification is good for replace the 2sd1577, but only a note, the package of BU2508A is metallic and if you install it need a isolation from BU and heatsync, or you just buy a BU2508AF because the AF have a plastic package and not need a isolation (BU508AF is same package).

Probably you have shorted the collector with GND and this cause the issue on video in post2.

 

[demonlg]

And is not a BU250BA but it is BU2508A !

 

[spiny]

Just for info, i have verified the BU2508A and the specification is good for replace the 2sd1577, but only a note, the package of BU2508A is metallic and if you install it need a isolation from BU and heatsync, or you just buy a BU2508AF because the AF have a plastic package and not need a isolation (BU508AF is same package).

Probably you have shorted the collector with GND and this cause the issue on video in post2.

ah, yes, I did have it connected to the heatsink, so it was grounded. I will re-test with no heatsink

 

[spiny]

OK, thanks. I'll take a look at the schematics.

I am going to look for a power supply capacitor feeding the vertical dive circuitry.

If it is temperature dependent (of course) I would recommend a can of freezer spray and a hair dryer to find the faulty component.

Do you have an oscilloscope by the way?

Dave

I have a scope somewhere, but I can't find it :D freeze spray is a good shout, I'll get some ordered

 

[daver2]

Can you point me at some schematics (or service manual containing schematics) for your monitor?

I have found some but they don't appear to tally. There is a safety resistor and electrolytic capacitor feeding the supply to the vertical section of the circuitry. However, before I identify specific components, it would be good to ensure that we have the correct (and readable) schematic...

Dave

 

[spiny]

Can you point me at some schematics (or service manual containing schematics) for your monitor?

I have found some but they don't appear to tally. There is a safety resistor and electrolytic capacitor feeding the supply to the vertical section of the circuitry. However, before I identify specific components, it would be good to ensure that we have the correct (and readable) schematic...

Dave

it's this one:

Wave Forms - Philips CM11342 Service Manual [Page 18]

Philips CM11342 Manual Online: Wave Forms.

www.manualslib.com

photo of the sticker on my monitor:

 

[demonlg]

ah, yes, I did have it connected to the heatsink, so it was grounded. I will re-test with no heatsink

It's not good procedure testing it without heatsink, the temperature of this device going to high in many seconds, if you find a mica isolator you can make little plat of isolation to put from heatsink and BU2508A, and then check the screw if it is fixed with screw on heatsink, but probaly is it fixed with a spring.

 

[spiny]

It's not good procedure testing it without heatsink, the temperature of this device goung to high in many seconds, if you find a mica isolator you can make little plat of isolation to put from heatsink and BU2508A, and chek the screw if it is fixed with screw on heatsink, but probaly is it fixed with a spring.

yes, mine is foxed with a spring clip to the heatsink. I did try the BU2508A without the heatsink, only for a second, and it made the 'buzzy' noise, so its just not working. Swapping back to the 1577 allows the monitor to work normally again, but with the 'bounce' still present.

I have a BU508AF on order, which I will try.

 

[demonlg]

OK, if BU2508A have a buzzy noise it is in short circuit, is defective, or it is damaged from previouse test with heatsink!

 

[daver2]

Just to expand...

If the heatsink is not electrically connected to anything, it is not strictly necessary to isolate it. However, good practice would isolate the transistor from the heatsink...

If you fit a mica washer, you must also use heatsink compound between the transistor and mica washer and between the mica washer and the heatsink.

If you have a metal bolt, nut and washer, you need an insulating 'top hat' to prevent compromising the mica washer insulation.

Dave

 

[demonlg]

Just to expand...

If the heatsink is not electrically connected to anything, it is not strictly necessary to isolate it. However, good practice would isolate the transistor from the heatsink...

If you fit a mica washer, you must also use heatsink compound between the transistor and mica washer and between the mica washer and the heatsink.

If you have a metal bolt, nut and washer, you need an insulating 'top hat' to prevent compromising the mica washer insulation.

Dave

Yes, i have this model of monitor, and heatsink is connected to GND