Author Topic: tek 2215 (Read 6016 times)

andy3055 · « **Reply #50 on:** October 25, 2021, 07:21:52 pm »

Quote from: m3vuv on October 25, 2021, 05:59:09 am

Well i hooked up the eht to the crt and moved the whole lot to one side,heres a few readings i took,on q387 base i get 8.8v,it should be 2.6!,r290 wiper measures as follows,fully cw=3.44,fully ccw 3.4v,r190 is fully cw3.4,fully ccw 3.4v,dont know if this helps?

That poor change should give you the clue to the problem. this is the area you should concentrate on.

The 2 wipers are connected to 2 resistors R191 and 291. The other ends of those resistors are connected to -8.6 volts. Check if that supply is there. If not, trace back from that point to find where the -8.6 volts is disappearing.

Also check the +8.6 volts on one side of R178 and 278. If that is missing, trace back for the +8.6 volts.

m3vuv · « **Reply #51 on:** October 26, 2021, 12:20:59 am »

I get -8.6v on one end of r191 and r291 and +8.6v on one end of r178 and r278,tia.

andy3055 · « **Reply #52 on:** October 26, 2021, 12:51:47 am »

Those wipers should vary between 3.5 to 4.8 volts, 4.3 volts being the mid range, from what I see on the manual. I am not home to check my scope. I wonder if there is some sort of a poor connection where the leads from the pot is mating that board since it happens on both channels. May be you can re-seat any plugs in that vicinity, just in case!

m3vuv · « **Reply #53 on:** October 26, 2021, 03:30:24 am »

the voltages on the vert position pot wipers is as follows fully ccw=3.6v,halfway point =1.2v,fully cw =3.6v,there are no bad conections.

bdunham7 · « **Reply #54 on:** October 26, 2021, 03:58:28 am »

Quote from: m3vuv on October 26, 2021, 03:30:24 am

the voltages on the vert position pot wipers is as follows fully ccw=3.6v,halfway point =1.2v,fully cw =3.6v,there are no bad conections.

When the scope was all together, was the behavior such that if you rotated the knob all the way CCW the trace would be at on extreme (low, I guess) and as you rotated it CW, it would come up to a maxima somewhere in the center and then go back down again as you reached the CW limit?

m3vuv · « **Reply #55 on:** October 26, 2021, 07:09:13 am »

im pretty sure when it was together the controls operated normaly but just wouldnt move the traces more than about 3 divisions from the bottom,i understand what your getting at but no it didnt go up and down with knobs turned in one direction,although the wiper voltages say it should do,if it had i would of noticed that as it would of been odd.

andy3055 · « **Reply #56 on:** October 26, 2021, 04:32:01 pm »

Quote from: m3vuv on October 26, 2021, 03:30:24 am

the voltages on the vert position pot wipers is as follows fully ccw=3.6v,halfway point =1.2v,fully cw =3.6v,there are no bad conections.

Your cw and ccw positions have the same voltage?
Take a look at what I wrote earlier which is based on the service manual. Your readings will not make the cut.

m3vuv · « **Reply #57 on:** October 27, 2021, 10:59:43 am »

quick update q 350 base goes from -.273v fully ccw to +.456v fully cw,360 base fully ccw =+.392v to -.364v,only changes with pos 1 pot.

m3vuv · « **Reply #58 on:** October 28, 2021, 04:34:10 am »

well i managed to get some more readings before a 10nf riffa cap that i had missed blew up!,on q360 emitter i get 1.129v on q350 emitter i get 0.574v,q386 base reads-4.8v should be -4.3v,q387 base reads-4.099,should be +2.6v,also is the size of the riffa caps critical as i am struggling with replacements,it should be 10 nf all i have is 2.1nf at 8kv.

m3vuv · « **Reply #59 on:** October 28, 2021, 04:45:27 am »

sorry the caps i have are 2138nf not as i said before.

m3vuv · « **Reply #60 on:** October 28, 2021, 06:39:38 pm »

some more readings, Heres what i measure in respect of ground
q377 C=1.8v E=-2.1v B= -1.5v
q387 C= 21v E= 9.4v B= 9.9v
q376 C= -2.3v E= -5.6v B= -4.97v
q386 C=9.5v E= -5.7v B= -3.1v
thats with ch pos pot about halfway.

bdunham7 · « **Reply #61 on:** October 28, 2021, 07:22:15 pm »

Quick transistor troubleshooting tip--V_be should always be about 0.6V or so (or -0.6V as the case may be) and when it isn't, something is wrong. In this case Q386 has a V_be of 2.6V, which means it should be saturated on, but V_ce is 15.2 V. Unless I've made some obvious error--which I do regularly since I can't keep left/right, +/- or PNP/NPN straight in my head--it looks to me like Q386 is bad.

m3vuv · « **Reply #62 on:** October 28, 2021, 07:44:59 pm »

well just an update,my hot air soldering gun arrived yesterday so used it to remove q386,tested it on my component tester off board and it read as a back to back diode!,hope thats the issue,just orderes 2 replacements for that and its twin,2 genuine phillips brf 96s transistors for £3.50,hope they fix the scope,if so it will stand me at about £25 and a few hours work.

m3vuv · « **Reply #63 on:** October 28, 2021, 08:01:16 pm »

would a bc-107/8/9 be ok as a sub just for testing to see if the vert deflection position control works?,tia m3vuv

bdunham7 · « **Reply #64 on:** October 28, 2021, 09:00:14 pm »

I don't know of any reason that any small-signal NPN wouldn't nominally work, a 2N3904 might even work OK up to a fair portion of the BW. Is your board noticeably discolored in that area?

m3vuv · « **Reply #65 on:** October 28, 2021, 10:10:33 pm »

no the board looks like new,no signs of heat.

m3vuv · « **Reply #66 on:** October 29, 2021, 03:54:13 am »

this is how q386 tests on my component tester out of circuit.

bdunham7 · « **Reply #67 on:** October 29, 2021, 04:02:02 am »

If that is one of the versions of the ATMEGA328 based tester, that would be one typical result indicating a bad transistor. What goes wrong internally I don't know.

m3vuv · « **Reply #68 on:** October 29, 2021, 05:59:24 am »

Well theres good news and bad news on this one,after subbing the duff transistor,i was replacing the crt,i found the horiz deflection plates a pig to get to so decided to extend the wires so i could connect them before pussing the crt into its socket,i had the scope on its side to do this as it was better to solder the wires back into the pcb,i then put the scope normal way up and fitted the crt,ok time to test,on power on after a few seconds smoke came from under the crt,i quickly unplugged it from the mains and turned it over to look at the underside of the pcb where sat a small coil of soler wire that had shorted out the underside of the pcb,powered it up againe to see both traces now sitting about 3/4 up the screen,its the oposit of the original fault!,also it sees no input on either channel and the traces only do a horiz sweep of about 4 divisions,i will wait untill the replacement bfr -96s transistors arrive and fit them and test againe but i feel its not looking good, angry over making sutch a stupid mistake!!

m3vuv · « **Reply #69 on:** October 29, 2021, 06:01:31 am »

yes it is,brought it as a kit,only issue is the zif socket isnt the best but as it was only about £8 i cant moan,its a very handy tool.

m3vuv · « **Reply #70 on:** October 29, 2021, 06:03:53 am »

the case is made up of scrap pcb material,i have a piece of veroboard with 3 pins on it that fit into the ziff socket with 3 small leads with insulated croc clips on.

bdunham7 · « **Reply #71 on:** October 30, 2021, 12:35:55 am »

Quote from: m3vuv on October 29, 2021, 05:59:24 am

Well theres good news and bad news on this one,after subbing the duff transistor,i was replacing the crt,i found the horiz deflection plates a pig to get to so decided to extend the wires so i could connect them before pussing the crt into its socket,i had the scope on its side to do this as it was better to solder the wires back into the pcb,i then put the scope normal way up and fitted the crt,ok time to test,on power on after a few seconds smoke came from under the crt,i quickly unplugged it from the mains and turned it over to look at the underside of the pcb where sat a small coil of soler wire that had shorted out the underside of the pcb,powered it up againe to see both traces now sitting about 3/4 up the screen,its the oposit of the original fault!,also it sees no input on either channel and the traces only do a horiz sweep of about 4 divisions,i will wait untill the replacement bfr -96s transistors arrive and fit them and test againe but i feel its not looking good, angry over making sutch a stupid mistake!!

I've misprobed and broken a few things, I like not to remember them too much. However, do be very, very careful working with those deflection plate pins on the CRT--never put any sideways force on them or pry against the glass, no matter how stuck they are. You can break things internally pretty easily, and in the worst case blow up the CRT and injure yourself. Worst case you cut the wire, then when the CRT is out you can get at them a bit better. Oh, and I haven't yet had the misfortune of shorting the board like that, but a lot of the times on scopes if I'm working on them with the case off, I'll turn them on their left side (CRT down). 2400 series are different, I jack those up with blocks and put a fan on the side. There's lots of volts at some points on the board, best to keep it away from anything.

m3vuv · « **Reply #72 on:** October 30, 2021, 04:52:12 am »

i realise that now! hindsite is a wonderfull thing!! lol

m3vuv · « **Reply #73 on:** October 30, 2021, 04:56:09 am »

Im not doing anything else to it untill i fit the replacement transistors after they arrive,at the moment q386 and q 376 are just random npn replacements from my junkbox,but at least the pos pots sort of work now.

m3vuv · « **Reply #74 on:** November 01, 2021, 08:47:05 pm »

well the replacement transistors are fitted,i now hove the trace for want of a better word adjustable but now have no sweep,did i mention i put the scope down on a pice of coiled solder wire,it shorted sommat on the main board as sommat smoked,pulled the plug but to late i think!,cant see any signs of anything beeing fried tho,all i get now is 2 dots on the screen,as if in xy mode,any ideas where to start,seems i fixed one issue and created a bucket load more,teach me to keep my bench clean!!p.s the only way i get anything on screen is by using the beam finder. tia


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Author Topic: tek 2215 (Read 6016 times)

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