ARCHIVED FORUM -- March 2012 to February 2022READ ONLY FORUM
This is the second Archived Forum which was active between 1st March 2012 and 23rd February 2022
Alf
As lonnie quite rightly points out....the printed boards and circuit diagrams can contain some inconsistencies and therefore its always best to replace components in the same orientation as they came out, after all they worked that way for forty years or so, have a look at the picture of one of mine, it shows from left to right OIC201/OIC202/OTR200/OIC203.....unfortunately OIC200 is out of shot, however the important thing to note is the clearly visable crossover of connections on OIC202.
Hello Craig,
Thanks for that !!
I have crossovers on both 0TR100/200 because they are fitted face-up !!!!!
Looking at the diagram 5-1 of the SM I would need a cross-over at. 0IC203/103 in order to realise connectivity to Pin4.....
Pin4 at P11 and P12 are connected to C of 0IC203 and to C of 0IC103 respectively.
am I wrong or is it 'either crossover at 202 or 203' ???
The connectivity check that Lonnie mentioned is ok !
Your thoughts ????
ALF
I mounted my OTR100/200 face down so didn't need to crossover, this was how the originals where mounted so I went with what I knew, take a look at this picture from my basket case thead, I will take mine apart this evening and post some detailed pictures of all the darlingtons for you to compare your own connections......
thanks Craig, that's most helpful :-)
please take a look at pic 1010197 from the SM 5-1
as Lonnie explained, you turn this over and compare the B C E marking from left to right at the top of the board at 0IC202 which is the next picture
you will see B E C from left to right.
I connected 0IC202 according to the ' B C E ' marking, meaning I do not have to cross-over wires......or am I completely nuts ?????
have a look at pic 1010196
that is how I wired 0IC202 and also look at the marking on the board, which is different from the SM diagram 5-1
I appreciate your dilemma Alf....
However as mine is connected up as per the photograph above and is fully functioning the odds are good that its correct ;¬) non the less as I'm not at home right now I would suggest you take a look at the solder side of the board and trace the collector connection from OIC202, from your picture of the top of the board it does look like it is connected to the emitter of OIC203.
Craig
OIC100
OIC101
OIC102...note the crossover
And finally OIC103 again complete with crossover......
Ok as I'm looking at these pictures they bring to mind a comment you made some time ago regarding the mica insulator not being present on the BD165 (OTR100/200)....my reply was that there wasn't one on mine either so there cant be a need for one. This may well be the case, however my transistors are mounted face toward the heat sink, this is how they left the factory (see TIP146 jpg above) and there is a fibre washer on the retaining screw also......this may be why there is no mica insulator present, I have just examined a new BD165 I have kicking around and discovered continuity between the metal plate at the back of the device and the collector......I know you have mounted your OTR100/200 with this plate up against the heat sink......this may be nothing....but I would take them out and replace them with new ones if they are now faulty and put them back face towards the heat sink making sure the screw is insulated from the metal plate with a fibre washer....and who knows ;¬)
thank you for all you support Craig & Lonnie !!!!
I have adopted "craigs wiring" - see the pics
sadly, the power-amp still plays up and RL1 kicks in
not much else to replace now
you may notice the installed Mica sheet to isolate OTR100/200 from the heatsink !!
That's unfortunate.....I know you don't want to hear this but it has to be said, given the number of cross connections and wrong orientations you have now discovered, including the possible problem with BD165 collector to earth, since you replaced all the transistors and diodes on your power amp channels its a good bet that something was damaged during this learning event......in short I would go back and replace/check all the components in Martins lists ensuring they all go back in accordance with what you have learned this time around.....do one channel at a time and don't power anything up until all components are replaced/tested.....remember, this is not about the destination, its all about the journey. And anyway what else are you going to do to fill in your time out there ;¬)
How did I ever find time to go to work ?
Of course, that was before I met B&O vintage components:-)
To more serious business:
I started with the rehab proceedings re-replacing the TO-92 transistors in one channel of the power-amp and
Disconnected all darlingtons - they all measured ok ! - incl OTR100/200.
Next thing will be a diode D 200-205 re-check - cap 238 had been replaced again before.
I feel its unlikely the newly replaced resistors are now all dead ?? Is it ??
I know it doesn't sound very plausible but something is trying to tell me it is not necessarily a component in the power-amp section
But perhaps somewhere in the connecting wiring ?!
in theory I could replace all components in one channel of the power-amp and it should work, shouldn't it ?!
Anyhow, I will be back !!!
As Martin will point out it only takes one device to fail and you can expect an avalanche of failures across the amplifier, to be honest when going through this exercise with my "basket case" I also replaced all the components you have replaced and still the RL1 stubbornly kicked in when I powered up....I had however replaced half the components i.e. the Darlingtons and some of the TO-92's but not all of them before inadvertently powering up the machine, I thought I was plugging in my soldering iron but plugged in the Beomaster by mistake! nothing went bang or smoked but the RL1 kicked in......I quickly pulled the plug and went about replacing the balance of the components following which the RL1 still kicked in. My thoughts where that in powering up prior to replacing all the components the faulty one had caused a failure in one of the new ones I had installed. with this in mind I set to removing them all again and replacing them one by one.....in doing this I tested each one cold and none of them came back as failed, however when I powered up after finishing this recent change out the RL1 remained healthy, and has been so ever since. So...was it a poor solder joint/dry joint or maybe an oversize blob of solder across a transistor causing a short........some things mortal man is not intended to know ;¬)
Getting back to your machine, your RL1 only kicks in when you plug the +/-35 volts to either channel, prior to this the 15vdc supply to IC3 is present but RL1 is not energising so the problem looks like it has to be related to applying the 35v to the amp sections....looking at the circuit I can only see 2 ways the relay can energise:
1) bias TR16..this will drag down the base of IC3 and switch it on....IC3 will in turn bias TR15 at the same time it energises RL1, the emitter of TR15 will bias TR16 and latch it in when the 35vdc is interrupted by RL1 kicking in. to set this in motion DC is required at R45 and this can only come from the output stages.
2) An increase in resistance of R40, this will also switch IC3 on but will prevent the latching of TR15/TR16 so when the temperature drops to normal RL1 will reset itself, all of this should only happen if R40 gets hot....however you do say in your earlier posts that you measured 50ish ohms across this thermister, but that this jumped up to 320 ohms when you powered up.....how did you measure this?
hello Craig,
let me answer the questions related to PTC R40, concentrating just on that one channel for now:
receiver OFF, R(25) = 59.8Ohm with one leg lifted from the board - practically doesn't change when measured on-board though.
receiver ON, P12 disconnected :R40 jumps to about 306Ohm, measured on board - RL1 does not engage
receiver ON, P12 connected : R40 jumps to about 306Ohm, measured on board - RL1 engaged
please note: all TIPs (output darlingtons) have been disconnected on that channel !
I am just not sure whether this is how PTC R40 should perform but do not trust this device as the resistance reading are somewhat erratic ??
as for TR15 and TR16 and IC3 - all three components have been replaced previously but will re-check those transistors again.
Go look in the manuals section here and pull up the BM4400 design principles manual, section 28 (protection circuits) gives a good description of what R40 PTC is all about, wont solve your problem but provides an insight into its operation......
Alf....yes mine are also 25 turn trimmers, so long as you have the centre leg extended........which you seem to have, then the orientation of the trimmer doesn't matter.
craig
Thanks Craig,
Just been curious but also shooting at everything that shows a 'trace of hope for recovery' :-)
Yes, ''my'' center-legs were extended on those trimmers.
Now have to find a way to 'extend the brain'
Hi everyone,
i have resumed work on my BM4400 !!
in the meantime I took out the RL1 relay and cleaned the contacts - no change with the core issue !
however, something new to report:
when both poweramp channels are disconnected - the DBT stays dark, RL1 does not come on
connecting the right ch - the DBT illumintes brightly, RL1 does not !!! come on but idle current can not be adjusted via trimmer R277 ???
connecting the left ch - the DBT illumniates just moderately briefly until RL1 comes on and idle current can not be adjusted as there is not power.
connecting both channels - the DBT illuminates brightly but RL1 dos not !!! come on - idle current can not be adjusted for either channel !
that seems to be a new delevopment but dors not help !
the current idle current reading on both channels is about 132mV ........ way out ! Why would those new trimmers R177/277 be without any impact?
can someone please help ?
Jacques
Hi jacques,
just ordered a semiconducter tester from Peak Electronics and will again check transistors in the power amp section.
in other words, work is been put on hold ad I am no longer willing to trust those multimeter tests of transistors - you surely agree I presume?!
cheers
Hi Alf,I like the PEAK transistor/semiconductor testers and own a couple of them. They are an excellent tool. Just keep in mind they don't cover every failure scenario. They can measure and give you the transistor/diode characteristics and identify the device contacts (B C E). However there are still situations where a transistor or diode fails under load. The PEAK tester can't perform that type of test. What it can do it does really well and I use mine quite frequently.
Regards,John
Hi John,
yes, wouldn't it be fantastic to have a tester that uncovers all dodgy parts and make the job easy 😸
I sincerely hope that device would at least be more reliable and competent than the basic multimeter when it comes to transistor and diode testting !
whatever the problems are, there must be a common fault in both channels that engages the relay ?!!
the other odd thing is with the channel that does not engage the relay but can not have its idle current adjusted ??
As I understand if the relay engages the power is cut and there is nothing to adjust.
once the tester has arrived I shall again check the power transistors again to make sure there are no fake parts installed.
I am not giving up yet 🤡
Cheers
We have one of them testers right here......it's called a "Dillen", I'm not sure if a tester will be able to prove a Darlington transistor?
Too right Craig,
but he is most times out of stock or "currently unavailable" 😳
We'll see
Oh, you wouldn't want me to uncover my dodgy parts...
Martin
Quietly confident everything is prestine, for the electronic parts I couldn't vouch which would not matter anyway being referred
to as "the tester" 🤡
There are only 8 TO-92 transistors per channel in the power amp section plus the chassis-mounted ones
i revisited all in one channel but all tested ok !
could you clarify for me once again your understanding of 'drivers and pre-drivers' so no misundertsanding is happening.
cheers mate !
Hi Alf,
I'd replace the ones circled here on the dubious channel. Also replace the diodes, don't count beans here. Sometimes, the transistors check OK but they are bad under strain, leading to funny operation.
Also test the protection circuit itself. On one BM4400 I repaired, I had to replace a transistor and a diode there too.
Hi Jacques,
thank you for your reply, the tour is done and dusted.......not so my BM4400
well, this is what I found
TR115 hfe=228
TR116 hfe=249
TR117 hfe=334
TR119 hfe=161
TR120 hfe=170
these are all typical figures - I will get back to D104/105 and OTR100 and check those as well.
after so many parts replaced and hours spent I certainly won't engage in bean-counting 🙄
also, both transistors and IC3 in the fault switch measured ok!
Martin mentioned some other resistors I will check - and there are still the big chassis-mounted darlingtons ??!!
All of those are branded and came from sellers the likes of 'little diode'
I wanted to reply yesterday but the site was down for a while, due to maintenance operations I hear.
The darlingtons are usually sturdy and reliable workhorses. Do measure voltages everywhere, as per SM schematics.
The small ones before them can be faulty, regardless of what you find on the Peak. Given their low prices, I would replace them all.
I have only good things to say about Little Diode, a bit expensive but no fakes from them so far.
well, if the Peak instrument is unreliable with those to-92 typ transistors what else can I possibly use for testing transistors to be sure
what I replace is actually working ?
sure, I can easily replace those eight transistors happily again but fear the same outcome ?!
I also believe the big chassis-mounted darlingtons are ok because I disconnected the big darlingtons from the main board
and connected P11/12 - and there is still the overload circuit active and RL1 relay is clicking in ?
there was no obvious problem in the fault switch circuit but something in the remaining poweramp section on the mainboard must be terribly wrong !
That is where the project stands right now 👿 And may not move in any directon positive ?
I know you have changed out all of the transistors on your 4400 more than once, they cant all be shot. Get yourself one of these magnifying lamps and have a really close look on the solder side of your amp section, the more times you remove and solder a component the greater the chance of causing damage to the tracks, blobs of solder shorting etc.......
Nice suggestion 😳
I could not have done what I did without a magnifier 😁
Infact I have two 😸
Sadly to get affordable ones with a decent lence diameter one is limited in the magnification as you
Perhaps remember from your physics classes ?!