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Commodore monitor 1084S-P and PHILIPS CM8833II

D

demonlg

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Now with repaired 1084 with support of hugo and dave, very best friends, i have to repair other two monitor, but if possible to recover one of two it's ok for me,
This two monitor are simply the same, circuit is the same, tube is the same, flyback is the same HR7533 model.
I have a new HR7533 not used, and the 1084S-P have another one new replaced year ago and worked for about 2 hours!

Now, both monitor stored for year in working condition, the 1084S-P buyed on line not working and when i replaced flyback it's going to working perfect, the our defect at the time was a high pithc sound on startup continuosly, the flyback results in short, replaced it and the H transistor. Powerswitch with the classic problem replaced with a simply panel switch placed in original position.

The CM8833II founded on a used material shop, on the road with one AMIGA500! Buyed all for 15 euro, in 2002 year, but when i have turned on it's working perfectly, lost front panel door, power switch with the classic problem, but working very fine, AMIGA500 too after replaced two RAM chip.

About 12-14 year i have moved both of us from the downstairs home to my new upstairs studio as I had flooded the basement over the years and the humidity was damaging many of my computers. Tuned on first (1084S-P) but nothing appenig, only leds come up and i hear the PSU sounds startup, the second (CM8833II) after 3-4 seconds is popped!

Opened both one year ago, and now both on my table from 1 year....first visual check nothing...

From the board of CM8833II i have desoldered all capacitors in PSU area, and i have desoldered one BC337-40 and one capacitor from PSU area needed for repair the PSU of 1084 in other post, and finally the optocoupler too, But i have all for replacing, only PSU capacitor not but i have to buy it.

Now starting this new adventure, tomorrow i'll try to reassemble the 1084S-P first and try to check again and power on again.

Please, anyone have schematics of 1084S-P in good readable conditions? I have found one but it's very poor to read!

Emanuel
 
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Ok, shematics is here, is the same of my two boards, i have opened 1084S-P1 (exactly model is same of CM8833MKII or CM11342)...
Next of eating time i try to power up...........💣
 

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I followed your previous post and repair of your other monitor was rooting for you to fix it and was happy you did! :)

I have a 1084S-P myself and got replacement flyback for it. My replacement was an hr7506. 7533 is for the S-P1 no?
 
Hi mbliss, good questions.............i have original parts mounted on my 1084S-P1 now, i don't remember if i have exchanged two flyback from CM8833MKII and 1084S-P1, but, the original philips CM8833MKII parts have this code on top:

AT2079-37591

an on hr diemen it's correspond to HR 7533 and report the compatibility with commodore and philips monitor in attached image, and at the moment it's corresponding with my two models.

But i have repaired in past one Commodore 1084S and it's have different part number AT2079-30102 and corresponding with HR 7506 replacement, in other case i have one old philips monitor, don't remember model now, but same electronics of 1084S and in effect it have an HR7506 flyback!

At the moment I would say that it is the case to make sure that the flyback is the correct one! You made me doubt :D

Emanuel
 

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Here any information of commodore monitors:

Commodore monitors

gona.mactar.hu gona.mactar.hu

According to this site the results is:

Commodore 1084 flyback AT2076 36731 or HR6489 (it's my monitor repaired in other post)
Commodore 1084P flyback AT2079 30102 or HR7506 (it's my other working monitor mensioned in other post)
Commodore 1084S-P flyback AT2079 30102 or HR7506
Commodore 1084S-P1 flyback AT2079 37591 or HR7533 (It's my monitor in this post) same as PHILIPS CM8833MKII monitor
Commodore 1084S-D1 flyback MSH1FCT31 or HR46045 (it's my other working monitor) Daewoo chassis
 
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At the moment i have measued and compared the yoke coils with my other same tube and the results is the same, not short. I'll try to soldering a wires in all PSU area output, this have a PSU in the same board of VDU, and then try to measure all primary voltage.
 
Voltage check:

All measured with wire soldered on the output solder point of PSU:

128v rail results 129,4v
28v rail results 28,3v
12v rail results 12,1v
9v rail results 8,7v
5v rail results 5,1v

All voltage seems to be ok, only 128v is little higest but this is not a big problem for now i have located the 128v ADJ, and the little differencies probably if because need an electrolityc recap, but multimeter results are very stable, don't have checked with scope.

The issue is, the monitor power up correcltry, without "flame or arc or anithing of abnormal" :D, I have connected a C64 in a LCA INPUT line and selected input from rear switch LCA.
The high FBT voltage is present.

I don't have image, the screen stay black, but if i turn off the monitor i have an instant flash with a horizontal line in the center, but only when I turn it off, while it is on I have no horizontal line.

The flyback is the original Philips AT2079-37591 or HR7533, in past i have replaced it with another new but have the same issue.

When it is turned off, in the flash moment I described earlier, I hear a discharge, like a residual electrostatic discharge, the classic frying type noise and an instant later it stops.

I don't hear any whistling except as soon as it is turned on and then it stops, no capacitors exploded, but I only kept it on for 1 minute, to measure the voltages.

I have not yet seen if the heater lights up the tube, but I suppose so since I see the horizontal line when I turn it off, on the other monitor without a working heater I didn't even see the flash when I turned it off, but will I check!

Next step? Do I check the tensions on the neck of the tube?

Attached the point of my wires soldered for voltage measurement. At the moment the component codes match the schematic, the schematics attached in previous post are good.
 

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Adding: the tube lightup... I tried to turn on both with contrast and brightness at maximum and minimum but the result does not change.

I have to admit that the position of the FBT with the adjustments inwards is quite a design error, to get to adjust gain and focus you need a 50cm long plastic screwdriver to get there from the opposite side!
 
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News, i have moved the g2 gain on the flyback and now i see horizontal line at center of screen...... So at this point I have to look at the horizontal! No ?

Let's say it's strange but in fact this flyback was mounted on the CM8833MKII, the potentiometer on the FBT was blocked by the manufacturer with enamel, probably this adjustment was ok for the CM8833MKII but not for the 1084S-P1.

The horizontal transistor in this case is a D1577, i have new one, but schematics part list report a BU508AF......mmm
 
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I think so the problem is on vertical circuit and not on horizontal....but check both.
 
Checked D1577 is good, then checked power on TDA3653B vertical power.....pin 9 is +vcc and 4 gnd, i don't have power on pin 9, it is 0 volt, i will check resistor and diode in the area of this IC.
 
This resistor is opened! +28v power input to the IC TDA3653B, vertical deflection, now or it's IC in short, but not if i test from ground and VCC, or other in the area. The R3563 restistor part number is a 4R7 (4,7ohm) and is located at the top center of video board rear of the color trimmer, and is directly connected to 28v rail C2445 from PSU.
 

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Actually, while I was writing the previous post, I pulled the card out of the monitor and did more precise checks, all the components involved in the area are good and within tolerance, so I decided to change the resistor and the monitor started working again! I'm really happy because this time I followed a logic taught by Dave and Hugo, without going randomly. You are great and you give me courage, now it's MKII's turn, I keep the discussion in this post, there are missing parts, capacitors, resistors, transistors that I took as spare parts, but I want to try ... see you in the next post as soon as I have all components missing and replaced.

I hope my posts can be useful for someone else in the future.

Emanuel
 
Notice on the schematic, how the 4R7 resistor has lines drawn beside it and an exclamation point nearby.

This is because it is a "fusible resistor" that behaves as a resistor and sometimes a fuse. It is not uncommon to find fusible resistors that have gone open circuit in VDU's. They can have failed through overload, but often also with just age. This is why when you replaced it, the vertical deflection sprang back to life. Though it might pay to replace the capacitor 2563, in case it had high initial leakage currents.
 
Yes hugo, its a fuse resistor...i have replaced capacitor in vertical area, not other on board because all seems to be fine. Now i have used monitor for about 1 hour and it's very fine.
What seems very strange to me is that this monitor was stopped about 12-14 years ago, working, but in a damp place, but just in case, both this and the other, however, bought on ebay but full of dust and dirt inside, they had a similar defect, two interrupted protection resistors (then the other 1084 which also had the power supply tampered with by the previous owner who must have tried to repair it without success). I think the moisture from the dust and dirt shorted it out somewhere.
 

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I am proud of your new-found diagnostic skills in this thread my friend!

Everything in the correct order and beautifully executed.

Well done on finding the faulty fusible resistor.

Dave
 
Yes Dave, you two have given me courage to face my fears with your hands inside a monitor. Now the only thing I regret is that 1 year ago I mounted a used flyback transformer, it was the one from the CM8833MKII that I have to repair, while now there is the new one on it, I didn't feel like unsoldering it again, so much if it should break I have another one that I will never sell to anyone :D

This weekend i'm going to Bologna (Italy) at the Nerd Show with my family, very big exposition of old computers, console and arcade games, and other, then i'm dedicate to the CM8833MKII.

Emanuel
 
Before departure, i have resoldered all removed component on the video board of the CM8833MKII, electrolytic capacitors, two ceramic resistors, one BC337-40, one 15nF caps and resoldered wires of focus and G2 on neckboard, and finally replaced power switch with another type.

Checked all protection resistors, horizontal transistors, vertical ic controller, SCR and coil yoke.
The flyback is new, or 14 years buyed and only few minutes of working.

It's ready to go for reinstalling on the case and for new tests, in first power output of PSU!

See you monday :D

Emanuel
 
Ok,
i turned on the CM8833MKII, a continuous whistle is heard, like a hiss, and when I remove the power it emits pulses and then stops. Nothing in flame or explosion :D

Symptoms of a short circuit.......probably flyback or H transistors?
 
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