Maker Pro
Maker Pro

Measuring Diodes in Cct.

Status
Not open for further replies.

Michael Studio1

Jan 5, 2018
494
Joined
Jan 5, 2018
Messages
494
The PSU in my Sanyo Beta VTC5000 has stopped working. I am testing all 16 Diodes on the 2 Cct. Boards: PW-1 (2 Zeners) & PW-2 (5 Zeners and 9 ordinary Diodes.) Using my Multimeter UNI-T model UT-61E (which has a Diode select button on the Ohms range). Should the meter read any v. when connected Pos. - Neg. across any Diode? When connected Neg.- Pos. across all Diodes they read about 0.7v. but when connected Pos. - Neg.4 Diodes read up to 1.8v. the rest shew OL. Is this a valid test method? . The Cct.diag. is available from: www.freeservicemanuals.com Michael of Studio1.
 

Martaine2005

May 12, 2015
4,345
Joined
May 12, 2015
Messages
4,345
Hi Michael, you should really lift a leg out of circuit for accurate measurements. But we all do a quick check like you have done. 0.3V-0.7V one way and nothing the other suggests the diodes are ok. I test zeners out of circuit and apply voltage from a bench supply. But you can sort of check them with an Ohmmeter. Relatively low resistance one way and very high the other may suggest it’s ok.


Martin
 

Michael Studio1

Jan 5, 2018
494
Joined
Jan 5, 2018
Messages
494
Thank you Martin. I bought this VTC new in the 80's. and with up to 100 Beta tapes filled with programmes from the T/v at the time - makes it worth the pursuit! I must confess I wondered about the veracity of 'In Cct.' testing . Lift a leg! OK I suppose it's best to lift the Pos. leg of all six Diodes - just to keep similarity in the equation. In the same PSU there's also a 15 contact Voltage Regulator chip: STK7216 which is quite possibly faulty - but I have absolutely no knowledge of how to test this! So I'll do the leg-up test on the 6 Diodes first and post a reply of the results. We now have a new ZD-915 Digital Temperature Adjustable De-soldering Rework Station in the Workshop which will make short work of the 'leg-up' situation!

Michael
 

Martaine2005

May 12, 2015
4,345
Joined
May 12, 2015
Messages
4,345
Sounds like you got just the tool.
What was the original fault? Is it a linear PSU?
You can download the data sheet for that chopper regulator.

Martin
 

Michael Studio1

Jan 5, 2018
494
Joined
Jan 5, 2018
Messages
494
Again my thanks, Martin, ALL the Diodes test OK (with a leg-up!) OL in fwd +/- and around 0.6v/0.7v. in rev. -/+ The problem then has to be that Voltage Regulator chip STK7216 - which is now on order. So I'm getting somewhere! Yes, that De-Soldering tool is an excellent investment. Fortunately my son Maxim is a BA in Theatre Technology
(currently working on a 'Load-In' at Nottingham Playhouse for their next Production). He bought this tool for our Workshop last week. So he'll be able to claim Tax relief on it! Last year he was recording the Bournemouth Symphony Orchestra for the Opera Season in Covid - they could not place the players in the Pit so it had to be recorded. That was for Park Opera near Chichester - and he records all the Final Dress Rehearsals at Glyndebourne. He's too busy to help such things as I need - for he's rarely at home so I am very grateful for your help.

Michael
 
Last edited:

Michael Studio1

Jan 5, 2018
494
Joined
Jan 5, 2018
Messages
494
Sounds like you got just the tool.
What was the original fault? Is it a linear PSU?
You can download the data sheet for that chopper regulator.

Martin
The original fault is still with us. Voltage Output = NIL The Voltage Regulator is shewing no readings at all on any of its 15 pins. and Yes that de-soldering tool is fantastic - and fast! A definite must for any electronic Workshop! On the PSU I have no idea whether it's 'linear' for I don't know how to tell this but I imagine that with the transistors in various forms of connectivity (reminiscent of Valves in push-pull) and all the smoothing that's going on in there that it must be 'Linear' - but I'd really like to know how to tell this from looking at its Cct. Diagram. Now I must download the data sheet - though the Cct Diagram I have of this PSU shews the inner workings of that STK7216 with its oscillator and P.W.M. Control. There's even a variable resistor built into it - though there's no access to that as it's all encapsulated. Ha-Ha!

Michael.
 

Martaine2005

May 12, 2015
4,345
Joined
May 12, 2015
Messages
4,345
Could you take some clear photos of the PCB and post them here?.
Somebody will be able to guide you with what to check.
You’ll probably have to resize the image to approx 300kB in order to upload it here.


Martin
 

Sunnysky

Jul 15, 2016
529
Joined
Jul 15, 2016
Messages
529
The schematic and PCB layout is avail here http://freeservicemanuals.info/en/s.../Sanyo/VTC5000/VTC5100/VTC5010/SCHEMATICONLY/ download PDF

If possible do in-circuit test for voltages that differ greatly from the schematic ( or a known good unit) is the best method for debug.
Clipboard02.jpg

1st check the fuse output for 240Vac
then 28Vdc then if OK and Caps are OK
12V is the output of the STK IC.
if dead
This can be replaced with a more modern OKI 3 terminal regulator
 
Last edited:

Michael Studio1

Jan 5, 2018
494
Joined
Jan 5, 2018
Messages
494
The schematic and PCB layout is avail here http://freeservicemanuals.info/en/s.../Sanyo/VTC5000/VTC5100/VTC5010/SCHEMATICONLY/ download PDF

If possible do in-circuit test for voltages that differ greatly from the schematic ( or a known good unit) is the best method for debug.
View attachment 55765

1st check the fuse output for 240Vac
then 28Vdc then if OK and Caps are OK
12V is the output of the STK IC.
if dead
This can be replaced with a more modern OKI 3 terminal regulator

Reply from Michael: re: Sanyo VTC5000 Beta machine PSU.
I have lifted one leg (the Pos. one) of all 16 Xistors and find, on a Diode test
with my multimeter set to Diode (in the UT61E this on the Ohms setting) they
are all reading correct. I checked the Full Wave Rectifier Diodes in Cct. and
they too were OK. Ergo there's only that Voltage Regulator STK7216 chip left.

With the Power ON there is no voltage appearing at any of the 15 connections.
This chip must therefore be the culprit and a replacement is on order. Currently
I am in North Norfolk at our seaside holiday place so I can do no more until
I return to my Workshop in September by which time the chip will have arrived.
 

Michael Studio1

Jan 5, 2018
494
Joined
Jan 5, 2018
Messages
494
Correct - the Blue Button - I believe it uses a higher Voltage to test Diodes - anyway having removed
one leg of each of the 16 Diodes I was able to test each of them 'Out of Cct.' The reading obtained
proved all the Diodes to be working properly and none were suspect. Then with all Diodes re-soldered
in place and the power switched ON I was able to check the only remaining suspect: the Voltage

Regulator chip STK7216. Of the 15 connections not one was shewing any Voltage. I had found
my problem. A replacement STK7216 is on the way and I can continue to enjoy my Holiday on the
very edge of the North Sea. Exhilarating!! I shall be back in my Workshop in September to report.
Michael.
 

roughshawd

Jul 13, 2020
248
Joined
Jul 13, 2020
Messages
248
1. Diodes need to have both legs out to test them.
2. The VCR systems were a switch nightmare... You probably have a switch gone bad somewhere.
3. Now you know what a backup nightmare is.. - now exponentially hinge it = PC backup
4. Nasa's new rocket is heading for the moon tomorrow... see it on NASA channel.
 
Status
Not open for further replies.
Top