MX5500 no audio, can anyone help?

10 replies

TomAland

Bronze

6 posts

Posted October 19, 2023 at 06:49 GMT

Hi All! I'm new to B&O CRT TV's, so trying my luck here. I was just gifted a "working" MX5500 (Europe version). When I came home to test it, I did so with Scart from a VCR. Picture on the TV is great, but there is no speech/music from the movie. The only sound I get is a high pitch noise, that varies if TV picture is static or all black. I have tried two other Scart cables, its all the same. Also disconnected the two front speakers, and connected another 8ohm speaker, same. So I suspect a component issue on some board. Did the MX5500 have a known issue when it came to audio? The TV is made in -89, should I go for a full recap and hope that solves it? It would be nice to hear from someone with MX series repair experience. I'm an electrician myself, so I wont be completely lost when it comes to faultfinding the internals. Would be nice to have the schematics tho... Thats all for now, Thanks in advance. Tom

Electrical Engineer in the offshore oil drilling industry.

solderon29

Gold

43 posts

Posted October 21, 2023 at 09:54 GMT

#704573

These are great telly's,but they do have number of "usual suspects"when things go wrong. Do you have a user guide,as you need to investigate the set up,which is done via on screen guides and the remote control. The set has a variety of audio set up options,and your's may have been used with external 'speakers,or as part of a Beolink system,where the tv sound was relayed via a seperate compatible B&O audio set up? The squealing sound you mention seems a bit sinister,suggesting that something is amiss. Re-capping,particularly of the power supple module is standard practice with these sets,if no previous work has been done.Wholesale re-capping is not usually necessary and can introduce new problems too! Nick

TomAland

Bronze

6 posts

Posted October 21, 2023 at 12:01 GMT

#704577

Hi Nick, Thanks for the reply. I dont have the user guide, as I also suspected some sound setting to be wrong. I have no clue what the ex owner had hooked up, I know he had a lot of B&O equipment, so TV might have been outputting to something else. Also wanted to get in to the service menu, but haven't been able to do so from the remote, might have to do that "hack" on the board. What do you mean by wholesale recapping? Thanks a lot! Tom

Electrical Engineer in the offshore oil drilling industry.

solderon29

Gold

43 posts

Posted October 22, 2023 at 10:24 GMT

#704595

Ok Tom. Try "option programming" first. Assuming that you have the original Beolink 1000 remote control? With the tv in stand-by,press the PICTURE button,followed by the 1 button,then STORE,and the standby light on the set should blink . Switch the set on,and if you now have sound-goodo-sorted? If not,try pressing SOUND-1-store. If still no go,then there is a problem,alas,but no doubt fixable Don't be tempted to tinker with the "service mode" yet.I suspect that this is what you mean by "hack on the board"? Wholesale recapping means replacing all the electrolytic capacitors,as recommended by some,but it's rarely necessary,and can in fact introduce more problems. Better to work methodically? From your discription,it seems as though the set is essentially functioning,so it should'nt need much work. Nick

TomAland

Bronze

6 posts

Posted October 22, 2023 at 18:05 GMT

#704623

Thank you so much Nick for this advice! I will try this tomorrow as the TV is in my workshop on the other side of town. Yes I have the original remote, so I'll give it a try. Yes by hacking, I ment installing that button in the back to get access to service menu, but I'll wait with that then. Yes you're absolutely right, I wont dive off the deep end here just do methodically as you suggest. Thanks for the encouragement, on the Facebook group for B&O repairs I was advised to bin the TV as "it's going to be too much work". I beg to differ... Tom

Electrical Engineer in the offshore oil drilling industry.

TomAland

Bronze

6 posts

Posted October 23, 2023 at 13:35 GMT

#704638

Hi again Nick, So I did Picture->1->Store and got a blink from the red led, this was in stby mode. But upon turning the tv ON, the sound issue was the same. I guess the next thing is to open the TV and check components, wiring or other visible issues. Will update here.

Electrical Engineer in the offshore oil drilling industry.

solderon29

Gold

43 posts

Posted October 24, 2023 at 18:21 GMT

#704693

Ok Tom. What about the other options,sound 1,2,3? These are to change between the internal speakers(1)internal and external speakers(2)or just the external speaker's(3). If still no sound,then yes indeed internal inspection is the next step,but great care is needed! There are very high voltages present inside crt tv's,even when switched off! Are you aware of this,and confident to proceed? If not,it may be best to enlist the help of someone experienced? Nick

TomAland

Bronze

6 posts

Posted October 29, 2023 at 15:16 GMT

#704808

Hi Nick, Don't worry. I am 50 years old and Electrician / El.Engr. since almost 30 years, I know the dangerous parts in a CRT. Options 1,2,3 are all the same, makes no differences to the noice which one I select. Brgs, Tom

Electrical Engineer in the offshore oil drilling industry.

solderon29

Gold

43 posts

Posted October 29, 2023 at 16:54 GMT

#704818

Ok Tom. The sound selection needs to be "sound",then either 1,2 or 3. The selection of internal or external speakers is carried out by a relay,so I would expect that in sound mode 3,there would be no sound at all,without external speakers connected? As you are using an external source and not the internal tuner,it suggests that the problem is in the main audio control circuit (IC1)on pcb 5,or the output stage which is on the main board(pcb10).The output chips are located at the rear edge of pcb10 closest to the crt. With the set unpowered at this stage,slide the chassis out,and check the printed circuit around the output chips and the relay for dry joints,as the parts can push through the solder here. if nothing is obvious,we can then get technical with a meter? Nick

Stoobie

Gold

986 posts

Posted October 29, 2023 at 17:09 GMT ? Edited October 29, 2023 at 17:15 GMT

#704820

Is there not a button on the front of the TV? If I recall there was a Power Button, one that steps through through the channels and the third cuts in/out the speakers for listening with headphones or connected speakers. Also, there may be a setting in the menu that deals with the PowerLink connection. If the previous owner had connected speakers and the PowerLink setting is on, it may cut out the internal speakers. Stoobie

Exeter, Devon, UK

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