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
Here is the simulation of the "Off" state
Here is the "On" state
Thanks John,
i will check which of those voltages I am able to verify and report back.
tripple checked the TR21 positioning.... its center leg is the base and it is fitted the correct way....
I would have been absolutely delighted about making that mistake But it would be difficult to put the base leg into the emitter hole and fit the rest.
bear in mind the platter spins the wrong way in StBy/Stop mode!
also, depending which probe - red or black - goes to TR21 C and which to Ground ? Will give you a “- or +” reading.
ALF
I think the platter going in reverse is a result of the failure of the "Off" switch circuit. The microcomputer is in standby mode so it doesn't react to any turning of the platter. The 15 VDC not turning off results in the brake circuit voltage that drives the platter backward. Yes, measuring the DC voltage with the probes backward will change the sign but the voltage value will be correct. I think you need to look at the on/off circuit as the point of failure. See why 1TR21 cannot drive its collector point to ground. One other thing...double check the base of 1TR21 (one more time). What are the two voltages the 1TR21 base sees? At one time you said that is oscillating so you need to verify again that the signal to turn off from the microcomputer is received there. If that is the problem then that would be the source of your problem.
I checked those voltages from the simulation in “OFF” position.
ground used was the -pol from 1C27:
Mine Yours
P1. 15V (16.1V)
P2. -0.85V (0.695V)
P3. -1.4V (50mV)
P4. -16.9V (-4.57uV?)
P5. -17.5V (-24.2V)
P6. -23.5V (-24.2V)
P7. 0.2 VAC (-3.54uV?)
P8. 18.7 VAC (17.4 VAC)
P9. 18.7 VAC (17.4 VAC)
P10. -23.8V (-24.2V)
P11. 23.1V. (24V)
there were obviously AC and DC voltages in your simulation diagram ?!
the base of TR21 is 0.8V. (Or 0.55V with ground being the keyboard chassis ground) In play mode after hand-braking the platter to ensure clockwise spinning.
at StBy/ STOP mode the reading at TR21-B is jumping all over the place independant from the ground choice!
ALF: I checked those voltages from the simulation in “OFF” position. ground used was the -pol from 1C27: Mine Yours P1. 15V (16.1V) P2. -0.85V (0.695V) P3. -1.4V (50mV) P4. -16.9V (-4.57uV?) P5. -17.5V (-24.2V) P6. -23.5V (-24.2V) P7. 0.2 VAC (-3.54uV?) P8. 18.7 VAC (17.4 VAC) P9. 18.7 VAC (17.4 VAC) P10. -23.8V (-24.2V) P11. 23.1V. (24V) ALF
You have some of the values incorrect from the simulation "Off" position
P1 (the 15V) is 16.1uV (microvolts) so it is off. P4 (-15V) is also off (-4.57uV).You measure on yours that they are full on ... +15V and -16V
Here are updated simulation pictures. I removed the extra probe printouts as I think they are causing some confusion. I removed the old probes and added new ones so be aware that the probe numbers are different now. Refer to the new ones.
Here is the OFF simulation
Keep in mind this is just a simulation so actual values will be slightly different. The key thing though is that your ±15 VDC supply voltages are not turning off in standby mode. The trouble-shooting task is to determine if the Off command from the microcomputer board is failing to switch off 1TR21 (the microcomputer certainly thinks it is)...or are one or more circuit components failing to execute the off command.
Here is the ON simulation.
So note in the simulation differences between ON and OFF that 1TR21 must control 1TR20 and 1TR19 to turn the ±15 VDC supply voltages on and off to the rest of the Beogram.
You mentioned that your 1TR21-Base voltage jumps all over the place when the Beogram is in Standby mode. Is the 1TR212-Collector also changing constantly with the base? I am asking to find out if the 1TR21 is turning on when it is not supposed to. If that is the case then you can look at the on/off signal coming from the microcomputer. I have seen problems before with the microcomputer board supporting components like the 4.7nF capacitors. Those are tricky to work on because of the very tight spacing and a number of the components have solder points on the component side and trace side. If those are not installed correctly it will cause various failures. Since your Beogram was working at some point before this failure then it is possible one of those solder points was weak and failed.
Ok, I had a look at my voltages again against your updated simulation:
Yours. Mine
P1. 695mV. -850mV
P2. -2.39uV. -16.9V
P3. 50.1mV. -1.4V
P4. -24.1V. -17.5V
P5. -24.1V. -22.5V
P6. -24.1V. -17.4V
P7. -54.6uV. -17.4V
P8. -54.5uV. -0.6V
P9. 5V. 5V
P10. 16.1uV. 15V
P11. 24V. 21.5V
P12. 24V. 22.2V
P13. 24V. 20.8V
P14. -24V. 0V.
P15. -19.3VAC. 18.3VAC
P16. 17.4VAC. 18.2VAC
ground as usual drom -pole of C27.
I hear what you are saying about suspect solder joints in the processor box 🙄
after I replaced the old uP socket I double checked the uP chip has been installed correctly without one of its pins bent or missing the contact
(easily done with 40 pins).
i also checked the soldering on both sides of that PCB for suspicious/cracked joints....as far as I could see with my 8x magnifier all fine !
it is a bit hard to belive all of the TR21 replacements are faulty ?? Having said this the TR18/19/20 have all been tested before been replaced.
I will get on to the updated ON simulation to verify its readings.
John's. Alf's
P1. 695mV. -850mV Were your probes reversed here? This won't turn 1TR21 on (for the Beogram OFF state).
P2. -2.39uV. -16.9V -16V should be off
P3. 50.1mV. -1.4V This doesn't look right
P4. -24.1V. -17.5V P4, P5 and P6 show that 1TR19 is on when it should be off.
P11. 24V. 21.5V P11 and P12 show that 0TR1 is on when it should be off
I don't see much point in going through the ON state as the OFF state is the problem. If your P1 measurement is accurate then you appear to have a problem from the microcomputer circuit where 1TR21 is not actually being turned off. I don't see how you are getting -1.4 V at 1TR21-C though. That looks suspicious to me but I haven't checked one of my Beogram units to confirm. I'm afraid you measurement results are confusing. The only effect the microcomputer has on this circuit is the On/Off signal. So if your measurements are correct then 1TR21 is not getting an OFF command. That voltage (PR1) at 1TR21 should be around +0.7V.
ALF: it is a bit hard to belive all of the TR21 replacements are faulty ?? Having said this the TR18/19/20 have all been tested before been replaced.
The results don't have to mean that there are faulty transistors. The thing is this power On/Off circuit has one input, the On/Off command from the microcomputer board. If that is not working then your problem is that direction. If the On/Off command is working then you should see 0.6V to 0.7V at the base of 1TR21 and the 15V supply voltages should go to zero. If that doesn't happen then the source of the problem has to be from TR21 out to that power control circuit which involves TR19, TR20 ...and TR18, 0TR1. However, there are other components and connections in that circuit so I would look at everything. But start with 1TR21.
Your revised OFF simulation diagram has disappeared ?
No, the probes were not reversed -
I had the collector leg lifted at TR21 and connected via a jumper to see the difference in voltage at TR19/18.
when reconnected it may have briefly come off during measuring ?
Whatever, it is now properly reconnected and the reading is still a “- reading “ not anywhere near 0.7V !!! 🙄
also rechecked for the xth time P6 pin4 ( from where the ON/OFF signal is going to B-TR21):
in OFF-mode it was mostly around -1.1V (not a 100% steady) and that is exactly what B-TR21 sees - C-TR21 is around -1.6V
you may find those readings confusing but as said, I can only report what the instrument tells me - it is way off 0.7V target 😡
all that time platter was spinning in reverse !
0TR1 is correctly wired and can only do what the on/off circuit dictates, which is not what we get - again, connections have been
tripple-checked.....no adverse findings.
there is this uneasy feeling about the uP which does NOT send out the right signal via P6-4 ?
yes, I could go back in the uP box and check connections and joints again.....would that achieve much ?
as I understand, there must be different task-sections within the uP chip as it seems to do everything else right after initially
hand-braking the platter so play can go under way.
are we really looking at a “light-switch” intergrated into the mains cable ?😳🤯 i can’t believe it.
The off state diagram is still in the thread a few posts up.
I believe your measurements but they don't make sense to me. I don't see the microcomputer putting out -1.1V and I am not seeing how the 1TR21 collector gets to -1.6V. Have you monitored the +5VDC supply while the Beogram is in the ON and OFF states? I think there would be a lot more problems with the microcomputer if the +5V was unstable so that would probably be a reach to suspect that. I am afraid I am out of ideas for now.
I wouldn't add a switch as a means of utilizing the turntable. There is something wrong with the electronics so inserting a work around like that is asking for more trouble I think.
I would reach out to Martin to see if he can shed any light on this.
Yes, I believe you totured yourself enough for now 😕 and I can not thank you enough for it!
the +5VDC supply at P6-1 only varies between + 5.05-5.01 VDC according to OFF/ON mode change.
the closest I could get to 0.7V at P6-4 was about -0.770VDC, same at B-TR21 but that signal is not steady - you measure at different times
and get different readings.....impossible to get a fixed reading plus it is always negative ?? No fault of my own, probes are connected correctly.
again bear in mind the platter does spin in reverse all the time unless hand-braked for Play mode.
as I see it, the uP must get some kind of interferring signal from elsewhere that prevents to send a steady signal from P6-4, meaning not being ready
beyond doubt for a steady OFF signal....why on earth would it oscillating ?
that is at least my humble theory - right or wrong ?!
the revised simulation diagram is there but does not open ?.....oh, the light switch should not be taken seriously rather a thread to the BG 😡
Hi,
what John wrote here:
sonavor: ... I know other people have asked before but are you sure you have the pinouts correctly mapped on your 1TR21 (BC547B) transistor? For example if you had the TR21 base going to ground instead of the emitter then TR21 would behave as you are seeing it behave.
... I know other people have asked before but are you sure you have the pinouts correctly mapped on your 1TR21 (BC547B) transistor?
For example if you had the TR21 base going to ground instead of the emitter then TR21 would behave as you are seeing it behave.
reminded me to some trouble in the eighties or nineties (?) with some transitors with the same specs and name but different pinout depending on the manufacturer. I think it have been the BC547..549 and 557..559 types but being not sure, it's a long time ago
The 'official pinout was ' E - B - C' used by the most manufacturers, but one or two used ' B - E - C ' ! ! This would give the readings as John stated before.
I would recheck the transistor desoldered. Ether with your multimeter, or if you use a transistor or 'universal' checker watch for the pinout on the display! ( Functional Pin -> Pin Number!)
Now if the transistor is desoldered you should be able to measure the On/Off signal from the microprocessor at the connection where the base of the transistor belongs to. And aditional connect a switch between the emitter and the collector pins to simulate the processor which means switch the +/- 15 V on and off.
This way you can see where the problem lies: getting around 5v and 0V at the base connection => µp is fine. +/-15V can't be switched on or off manual the problem is in the switche power supply.
Ralph-Marcus
Well, without the TR21 on board I get a reading of 4.9VDC at the B-connection of TR21 in both cases ON and OFF ?!
a removeable jumper between C and E would do the same as a switch, wouldn’t it ?!
if so, 15V remain on !
when you say the problem then is in the switched power supply meaning TR21 / 20 / 19 / 18 excluding 0TR1 ?! Or the power transformer ?
I have been through the process of checking thus group of transistors involved in the power on/off switching ??
PS all transistors are tested with a PEAK tester, mapping out the pins, etc....
ALF: Well, without the TR21 on board I get a reading of 4.9VDC at the B-connection of TR21 in both cases ON and OFF ?!
This should give ~ 5V (On) and ~ 0V (Off) ! You can try a simple diode (1N4148) Anode in the base connection and cathode (the one with the black ring) connected to the emitter connection. Now you should get some thing like ~ 0,6 V (On) and ~ 0.1 V (Off) could be that the processor needs some 'load' to give measurable output.
ALF: a removeable jumper between C and E would do the same as a switch, wouldn’t it ?!
Well not as nice but if you can 'switch' when the device is connected to the power it should work :)
But if it doesn't switch off the + / - 15 V supply some thing is wrong in this corner.
The transformer should be completely out of the game because it produces the 5V supply and it gives power to the + / - 15V supply
ALF: I have been through the process of checking thus group of transistors involved in the power on/off switching ?? ALF PS all transistors are tested with a PEAK tester, mapping out the pins, etc....
Sorry to insist but please double check the pin mapping with the PEAK tester: green= ??, red=??, blue= ?? . Also be careful to not exchange C and E this renders the operation of the transistor. The hfe (gain) of the transistors should be between ~ 250 and ~ 400.
ALF: a removeable jumper between C and E would do the same as a switch, wouldn’t it ?! if so, 15V remain on !
Hi Alf,
So with a manual jumper between 1TR21 - C and E the 15V supplies remain on? That means the problem is on the side of the circuit that the 1TR21 collector is on. The only function of the microcomputer is to turn 1TR21 on and off but bypassing that the problem remained so I think that eliminates the microcomputer as the problem. When you manually grounded 1TR21 - C the 15V supplies should have turned off so there is some problem in that area. When you manually applied that jumper did you have zero volts at the emitter of 1TR20 ?
Thinking about this yet again...It is interesting and unusual that the problem is the power supplies won't turn off. It seems most of the time power problems are missing power. From your last revelation of using a jumper to attempt to turn 1TR21 off (by connecting 1TR21 collector to emitter) it tells me the problem (as Ralph-Marcus also noted) is on the power side of the circuit and not on the microcomputer control side.
The other interesting thing is that whatever the problem is, it affects both the +15V and -15V supplies. Those two supplies have separate transistor controls though (0TR1 and 1TR19 respectively). A problem in and around 1TR19 would affect both plus and minus supplies though.
I looked back at some of your measurements when you were trying to match up with the simulation probes. At least one of them doesn't look like you got the right point measured. For example PR14 has to be around -24V and you showed 0V. But that is the source of the -15V and you showed that you had -15V.
Focus in on 1TR19 base and emitter voltages for the Beogram ON and OFF states. There should be a 0.6V to 0.7V difference in those when the -15V is on and near zero difference when the Beogram is supposed to be off. Your earlier measurements showed the 1TR19 emitter at -22.5V and the base at -17.4V. That means 1TR19 would be on and -15V is on (which is the case with your circuit). So why is 1TR19 not turning off? If 1TR20 has its emitter side grounded (per your jumper) then it will be off and the 1TR19 base and emitter voltages should measure close to the same value (keeping 1TR19 turned off). That apparently is not happening in your circuit.
The answer is NO 😕 to zero volts at E - TR20
next focus was on TR19 -E,B
I can only confirm the previous readings at E and B.
not changing whether I have TR21 in place or out and play only with that jumper to simulate on and off
absolutely no impact that I can see in the readings ??
this is seriously odd ?
I do however like the diagnose putting the uP into the clear as this leaves at least some hope OFF will be achieved in the end 🙏
Okay, so with the jumper in place that removes the microcomputer from this problem. Its function is to turn 1TR21 on and off. Using the jumper you still cannot get the 15V supplies to switch off so while that is a mystery it does narrow things down to the main board and an issue with the controlling components there. So that is a bit of positive progress. Yes, I would classify this as seriously odd but it isn't magic. There has to be a logical culprit you just haven't found yet. It is starting to sound like some sort of ground (bad ground) problem. 1TR21 - E connects to ground. If you jumper 1TR21 - C to E then 1TR20 - E has to be ground and 1TR20 has to be off.
Continuing with that... 1TR20 being on causes current to flow through R82 so 1TR19 - B is greater than 1TR19 - E turning it and the 15V supplies on.Leave the jumper to take care of 1TR21 and see what happens when you lift off R82's lead that connects to 1TR20 - C.Doing that should force both 15V supplies to turn off because no current should be taking the 1TR19 - B voltage higher than its emitter. At the same time, please report the voltage levels of 1TR20 - E and C.
That should also shed some more light on the problem. I hope this is another step closer as I'm sure you are too :-).
NO............😡
with TR21 removed, jumper connected C and E/ground of TR21 terminals, R82 leg connecting with C- TR20 out..... power is still on........🍷🍷🍷
This drive is getting power.... unless I take out the transformer ——— but from where ?
I simply don’t believe it - do we have to take out the complete ON/OFF circuit ?
Wow! That shouldn't be able to happen. So what did 1TR20 - E, B and C measure under that test condition? Do you still get -1.4V where you have the jumper? Also, what to you measure on the lifted R82 leg?
It kind of sounds like an undesired short to ground somewhere. It almost sounds like the node between R82 and 1TR20 - C are shorted to ground while the connection between 1TR20 - E and D26 is not connected. I am not guessing at that...I am just playing with scenarios on the simulator that end up with similar voltages you are seeing and result in the 15V supplies still on.
I don't know about all of the On/Off - 15 V supply circuit but I feel like the suspect area involves 1TR20, 1R82, 1C30, 1R81, 1R80, 1TR19, 1D26. Not necessarily bad components but maybe. The interconnecting wire paths (traces as well) of those components is also suspect.If you would, report on the measurements I requested in the first paragraph above. Then we might have an idea what to look at next.
Ok,
with the jumper connecting the C and E terminal of missing TR21, deck in OFF mode, platter spinning reverse
TR20 showed the following:
E = -1.9V, B = 0V, C = jumping between -0.150V and -0.900V
lifted leg of R82 = -17.8V
So 1TR20 should be a solid 0V with the jumper to ground (1TR21 - E to C). Since that is not a solid ground it appears that is one problem.With R82 lifted there shouldn't be any current flowing on that 1TR19 circuit but there is some path there because you have -17.8V instead of close to -24V (or whatever 1TR19 has at its emitter). That is a second problem. Maybe they are related but either way they shouldn't be the voltages at those locations.
I'm too tired to think any more on it for now.
Hi ALF,
John is correct, you can't have voltage at the emitter of 1TR20 if the collector of 1TR21 is properly grounded.
Instead of just using a link between C&E of 1TR21 why don't you try a link between C of 1TR21 and another earth point like the negative terminal of C40.
I'd try measuring the +/-15V supply with R82 added back, 1TR21 removed and adding a link from C 1TR21 to C40 earth.
Regards
Lonnie
Interesting suggestion from Lonnie (thanks Lonnie) connecting the jumper to C40 ground instead of using TR21-E ground.
looking again at TR20 voltages (thanks John):
with R82 in place: E = B = about 0V, C = -16.6V
with R82 leg lifted: E = B = about 0V, C = -0.62V. R82 leg = -16.6V
+/-15V supply still present !
Okay, good...there is a problem on th 1TR19 side. That's why we wanted you to check that.You should also see that 1TR19 - E is in the -22V to -24V range. But with the 1TR19 - B side being at -16.6V that transistor (TR19) is always on...causing the 15V supplies to always be on. There must be a path from 1TR19 - B to ground besides 1TR20. That is causing 1TR20 to not have any control over 1TR19 that it should. It is also looking like you have some bad ground connections as the new ground you used put the 1TR20 - E, D26, 1TR21 - C, R83 node at zero volts as expected (and intended). So the 1TR21 - E ground seems suspect and there appears to be some sneak-circuit ground that is affecting 1TR19's base.
With the Beogram unplugged what resistance/continuity do you measure between the 1C40 ground and the power supply circuit grounds - C24, C27, C29 and the transistor grounds of 1TR21 - E, 1TR20 - B, 1TR18 - B. Keep one DMM probe on the 1C40 ground and measure the other grounds to it. The resistance between all of those grounds should be pretty close to 0 ohms (although you might measure 0.2 ohms depending on your meter).
This is better than any criminal investigation series on net flix
Collecting Vintage B&O is not a hobby, its a lifestyle.
Continuity was - as expected - all over around 0.1 to 0.2 😕
from memory, it all started with a “simple” speed issue (fixed now), not to mention the everlasting mute issue that eventually left me cold
and out of the blue it wasn’t turning off anymore ?
That is a little surprising as your manual jumper of the 1TR21 - C (1TR20 - E) over to 1C40's ground provided a good ground where the jumper from 1TR21 - C to 1TR21 - E did not. If 1TR21 - E ground and the 1C40 ground are equal then the original jumper (1T21 - C to E) should have got you your zero volts at the 1TR20 - E node. I am confused by that.
If the grounds are all good then you would have to suspect 1TR19.
Tonight I was able to run a simulation in Multisim where 1TR19 - C and B have a fault (leakage of over 20K ohms) that resulted in bad/faulty voltages similar to what you are getting. So it is possible that the transistor is causing your problem even though it measures good outside the board. Some semiconductor failures do happen that way. 1TR19 is a PU01. In an old Beoworld post Martin said the 92PU01 can be replaced by 2SC4135 or BD507. What did you replace yours with?
I replaced the PU01 transistor with a ‘ZTX 751’ transistor as PU01 are no longer available....!
ALF: I replaced the PU01 transistor with a ‘ZTX 751’ transistor as PU01 are no longer available....! ALF
If you replace it I would try a different substitute than the one you are currently using. Martin should know a good one to use.
Alf, I found the original thread where you asked Martin about changing 1TR19 (PU01). He questioned why at the time. It sounds like you should have kept the original PU01 transistor for 1TR19. Do you still have it? If so I would put it back in the Beogram.
some encouraging news:
I found a PU01 transistor (hfe 240) - not sure though whether it was the one I replaced because of low hfe ??
I put it in but left TR21 out with its C jumper still connected to minus (ground) of C40.
platter stopped spinning 😁 so it obviously turned off the 15V supply! .....halleluja in Leonard Cohen’s words.
the question now is how to get back, putting the old TR21 back in its spot, connecting the jumper from its emitter/ground to ground of C40 ?
Good news there Alf. Yes, I think 1TR21 is fine. My simulation showed that a faulty 1TR19 could cause all of the bad measurements you were seeing. You confirmed that in a way when you retested that all of the grounds are connected. Put the 1TR21 back and the Beogram should be good.
Good job!
If you have the original 92PU01, I also suggest fitting it back.Else the ZTX replacement would be fine - if you can find original ones.Unfortunately, the market seems flooded with counterfeits and I can't help thinking, that the one you fitted could be such a case.
NTE128P would also work. I know that buying NTE you never really know what you are getting, but this is not a particularlycritical position (apart from the power control) and I'm sure an NTE would be good enough.
Martin
That simulation program of yours is indeed a fantastic tool, provided you know how to feed that beast 😁
and you do !!!!
everything has now been put back as it were and a loooong saga has hopefully come to an end:
it spins clockwise,
it turns and starts and plays plus
it TURNS OFF 🙏🙏🤗
a very big thank you to John, Martin and Lonnie for their endless patience and determination to help and crack that puzzle.
God might remember what spooked me to replace that PU01 ?
anyone for a drink ??
and for Sørens, he has to get back on net flux now....sorry mate !