Homag 512-4 osciloscope repair help  - Page 1
Forum section: electronics / repair

author: Ozoz_xba
author_rank: Newbie
timestamp: August 04, 2021, 12:56:52 am
content: Hi to all,I have an old osciloscope at firsthe had 2 channels and working well all buttons but after see inside the circuit board was very bad and wanted to clean the circuit board .first i take off the Y -plate circuit board and cleaned it ,ialso take off the tantalium capacitors (1uf35v) to check if them are good ,the capacity was 1 uf on all and esr about 3.5ohm on them after i installed them not changed to new ones at the not previus placed but different but as schematic sayed them are insalled .when i put the Y-Board back ,nothing is working now from the buttons and trimpots just intence pot is workimg and i have the screen like this in photo.i checked for the power supply and i have all the voltages on power supply and transformer.i have checkd the transistirs onnboard x and y and z and no failure.in which block should i look for just some kind of problems?may i have some opem resistors maybe?

author: MathWizard
author_rank: Super Contributor
timestamp: August 04, 2021, 02:52:10 am
content: Were any of the cap the polarized type ? Maybe put back backwards ? Or maybe the heat from soldering fried a cap ??This reminds me, I took apart an old oscilloscope months ago, that had lot's of little PCB's. I was re-capping it, then work got in the way and I forgot all about it.

author: Ozoz_xba
author_rank: Newbie
timestamp: August 04, 2021, 05:37:59 am
content: The caps were polarized cap but them are not put backward ,i have checked them twice .anyway i will check the voltages at Z circuit to see if sokething wrong there

author: bob91343
author_rank: Super Contributor
timestamp: August 04, 2021, 05:59:25 am
content: Possibly something didn't get reconnected when you reassembled.I have a similar problem with a Tek 2440 that I replaced two ICs and now can't get it working other than a strange display that is unaffected by any controls.

author: Ozoz_xba
author_rank: Newbie
timestamp: August 06, 2021, 08:44:24 am
content: No problem on the wires i think. I have found that i do not have 1 of the voltages in crt . I should have 130v in D1 connection but i just have 8 volts ,it comes from X1 ,T70 TRANSISTOR IS GOOD ,ON the other side of resistor 15k(4w) i have 250volt but 130v is not.i checked all the parts there all good working.do not know where to see

author: bob91343
author_rank: Super Contributor
timestamp: August 07, 2021, 12:37:42 am
content: Look at X1 and X2. Should be less than 1 Volt.

author: Ozoz_xba
author_rank: Newbie
timestamp: August 07, 2021, 02:26:08 pm
content: Quote from: bob91343 on August 07, 2021, 12:37:42 amDear bob thanks for trying to help me .i found the remain voltage on 130 volt .i have found the dot.but the dot can not go straight line and also can not move the dot up and down to Y lines .can it be vecouse of bad 1 uf 35 polarized tantalum capacitors .also time base want to wark ehere i change but it fails just show a straight line for less than 1 second when i change.should i look to x axes x board where timebase is .also dual channel not work .i have just 1 dot istead of 2 in dual that do not move...

author: bob91343
author_rank: Super Contributor
timestamp: August 07, 2021, 11:00:25 pm
content: If the dot won't move, it's likely that there is no deflection plate signal or perhaps the deflection plates are disconnected.If they are connected and there is no signal, it's the fault of the amplifier. Perhaps no supply voltage or no input signal.Once you understand the signal path and locate the components, troubleshooting should be straightforward.

author: Ozoz_xba
author_rank: Newbie
timestamp: August 10, 2021, 11:50:56 pm
content: Quote from: bob91343 on August 07, 2021, 11:00:25 pmThx in advance .i will try to repear it after 1 month as i am abroad now .will vhange first all those tantalium capacitors that have at 3.5 ohm esr .and after see for other problems on the amplifier.

author: Ozoz_xba
author_rank: Newbie
timestamp: October 30, 2021, 03:59:54 pm
content: Ok i now have the dot ,y axis , and i put an signal squere but have no x line just 2 points of the signal aquere that dont move on x line .i chexked a lot but there is nothing but on the sweep generator. I suspect on the transistor but them are checked and were good .anyore 1 of them should go bad when i open osciloscope and i have no x line .where should i look for?all tantalium caps are new with low esr.it looks like i do not have the sawtooth sighnal .where is it producked to look after it?

author: Ozoz_xba
author_rank: Newbie
timestamp: November 03, 2021, 04:06:19 pm
content: At least can you tell me where to look for the sawtooth wawe generator ?which traansistors generate it pls?

author: Ozoz_xba
author_rank: Newbie
timestamp: November 03, 2021, 06:43:46 pm
content: Ok thanks to all i repaired it .it was very small problem .i had put before bf199 transitor it wrong way from the socket.i reverset it and now i have the line .and squere wawe .on the scope the squere wawe is very long as i cant arrange it .anyway will se how to calibrate it.