1084s-P problem

[Impakt]

Hi all,
Today i was playing around with my amiga 2000 and 500. I only have the one monitor and a few times i unplugged/plugged the monitor from one amiga to the other without switching it off and now it's dead.

When I turn it on you can see it 'trying' to start up (the sound it makes is hard to describe, kinda like the high pitched startup sound it makes but on loop), and the sound is very low, almost like the amp isn't working. Power LED comes on fine..

Anyone know of any obvious things I can check? I'm handy enough with a soldering iron/multimeter etc.

edit: anyone have a copy of the service manual?

Thanks,
Impakt

[Loedown]

Check the 12 V zener feeding the line stage, if it's short circuit, replace vertical line drive, shorted diode, smaller electrolytic caps. Replace electros in power supply too, all secondary side.

Also check horizontal line output transistor for shorts, or open circuit on feed for horizontal, it's usually a small isolation transformer, resolder flyback transformer too.

If none of the above scenarios are right, write back here.

Paul

P.S. The high pitch squealing is usually the power supply starting, driving into a short and cutting out, then starting again, loop ad infinitum.

[Impakt]

Hi Loedown,
Got a service manual handy? If you're in Sydney, I'd be happy to pay for you to have a look at it. I don't know my way around a monitor so will need the manual to work what's what.

Thanks,
Impakt

[Anemos]

i think i have somthing from 1084 donot remeber if this type..

[Loedown]

Originally Posted by Impakt

Hi Loedown,
Got a service manual handy? If you're in Sydney, I'd be happy to pay for you to have a look at it. I don't know my way around a monitor so will need the manual to work what's what.

Thanks,
Impakt

I do have some circuits for a few monitors, but not 100% sure if 1084, but sadly for you, I'm in Melbourne. If you pay the freight each way and a moderate fee for the repair, yes, I will do it.

Paul

[Anemos]

Originally Posted by Anemos

i think i have somthing from 1084 donot remeber if this type..

in the zone ..

[xc8]

I just u/l on the Zone the service manual of the 1084P ..- very bad quality of scanned material.. it seens it was from a photocopy but..

have a nice New Year..

Chris

[Impakt]

Hi all,
Found some circuit diagrams here http://staff.washington.edu/rrcc/uwweb/1084PAL1
http://staff.washington.edu/rrcc/uwweb/1084PAL2

Based off this site, which has a heap of c64 info http://staff.washington.edu/rrcc/

What components on the schematic should i be checking?? I had a look at the ones posted (thanks!), but I'm no repairman so don't know which components i should be looking at.

Thanks,
Impakt

[xc8]

heh... Ray Carlsen's site! is a guru technician of C= equipment!


Chris

[Impakt]

Spoke to some repairer friends who tell me that the issue lies around TS467, a BU508A transistor, and the diodes around it (d465, d467, d468). Will report back if i make any progress!

[Loedown]

Originally Posted by Impakt

Spoke to some repairer friends who tell me that the issue lies around TS467, a BU508A transistor, and the diodes around it (d465, d467, d468). Will report back if i make any progress!

TS467 is horizontal line drive transistor, check for a short between emitter / collector, base / collector, it's usual for around 47 ohms to be read between base / emitter.

Check for dry joints on T401, horizontal line feed isolation transformer, S465 coil for O/C.

Voltage rails, 12V IC403 (7812), S491 O/C, regulator supply rail.
Voltage rail, 125V, measure across R494, check S491 for O/C
TDA2653 is Vertical Drive IC, check pin 9 for 26V

If all that fails, write back what you found

Paul

[Impakt]

with ts467 out i get 30M ohm between e/c, 0.76M ohm betweeb B/C

touched up solder joints on T401 and S465, problem still there.

IC403 has 5v between pin 1 and 2, 4v between 2 and 3, so the 16v input isn't right

[Impakt]

48.5v dc across r494
0.2 ohm across s465 when still in circuit, same with s491.
9.6v going to IC302 (tda2653), measured across pins 8 and 9.

disconnected power supply from the main PCB and i get ~127v DC coming out (measures across C144). Also the noise of the monitor changes to normal so the problem is obviously not on the power supply

when main circuit is plugged in again i get ~48v DC on C144, same elsewhere on the main board. C144 and the collector of the HOT have continuity. The problem seems to be related to the 125v rail at this stage.

Thanks for your help so far!

[Loedown]

Originally Posted by Impakt

48.5v dc across r494
0.2 ohm across s465 when still in circuit, same with s491.
9.6v going to IC302 (tda2653), measured across pins 8 and 9.

disconnected power supply from the main PCB and i get ~127v DC coming out (measures across C144). Also the noise of the monitor changes to normal so the problem is obviously not on the power supply

when main circuit is plugged in again i get ~48v DC on C144, same elsewhere on the main board. C144 and the collector of the HOT have continuity. The problem seems to be related to the 125v rail at this stage.

Thanks for your help so far!

You have a short circuit somewhere, I forgot to add that you usually need to check the TS467 out of circuit, but what you write doesn't sound right, normally they go dead short, it's rare for them to just go leaky. If I have a BU508 here somewhere, I'll check its resistance after I come back from dinner. The values of Sxxx are right, they're just coils to protect from excess current. In worst case you may have a faulty flyback transformer, they're a bit harder to check without proper testers, I always had access to a dedicated flyback tester, haven't bothered to investigate alternative methods since. Keep checking around the line stage / horizontal, that's where the fault will most likely lie.

Regards,

Paul

[Impakt]

so the transistor sounds OK? I'll check the diodes and capacitors around Ts467.

[Loedown]

Originally Posted by Impakt

so the transistor sounds OK? I'll check the diodes and capacitors around Ts467.

I wonder where I wrote that the transistor would be ok?

Going back to the schematic, I wrote the last lot without any reference, I also don't have any BU508, but 2SC5299, R456 partially sets resistance between B-E, C-E can only be influenced by the diodes, but their resistance would be greater than the resistance of the transistor. C470 or C478, runs from collector to earth may also have gone short circuit. Also check D465, the back EMF snubber diode S/C or O/C, it points more and more to the BU508 having gone leaky, as I previously stated, they usually go dead short.

Desolder all the pins of BU508 and check it out of circuit, leave it on the heatsink, it's still most likely to be the culprit, but check the rest of the circuit nearby, failing that, pack it up and send it off to me to fix.

Paul

[Impakt]

Hi Paul,
I checked the transistor out of circuit, my findings are: with ts467 out i get 30M ohm between e/c, 0.76M ohm between B/C

[Loedown]

Got diode check on your meter?

It sounds like the transistor is ok, but something is loading down the supply. Check all your voltage rails, then you should isolate them one at a time to determine which one is being loaded down, take a reading of what resistance you have on the affected rail and then search it out from there.

Paul

[Impakt]

yeah i got a diode checker on my meter. I'll start with D465 and make way from there..

edit: D465 looks to be dead (open). I'll desolder it and check again.. nope, it's fine..

[Impakt]

I took the BU508A out again and here are my measurements, they're different depending on the orientation of the probes. The component is on my desk, not on the heatsink.

| + | - |  Ohms  |
| B | C | ~0.85M |
| C | B |Infinity|
| C | E |Infinity|
| E | C | ~31.9M |

Edit: Just now i powered up the monitor without the BU508A, sound went away, and speakers are working again. Looks more and more like it's this part. I have a CM8833 and a CM8833-II too (which are set up elsewhere), so if I was desperate I could swap the part out just to help isolate it.