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-   -   Leak Stereo 30 Plus (https://www.vintage-radio.net/forum/showthread.php?t=192963)

Pcspike 21st Jul 2022 10:24 am

Leak Stereo 30 Plus
 
1 Attachment(s)
Recently acquired a Leak Stereo 30 plus with only one channel working, the problem is that it blows the 1.5 dc fuse each time it’s powered up. Both preamp boards are ok when used with the good power amp board.
I’ve checked the faulty power amp board, changed the electrolytic caps and checked all the resistors and transistors. However, there is a one single component that I’m having difficulty identifying, and suspect that this could be the problem. This components is linked between one of the terminals of P5 to the resistor R54. It looks like a resistor with the colours red, black, brown, and white on the body which doesn’t seem to relate to anything as far as I can see. I noticed that it looks very much like C31, a capacitor shown on the circuit diagram. Can anyone tell me what this is?
I found (on one attempt) that with the resistance turned up on p5 the fuse held but when I turned it down slightly it blew. Resistor R54 is ok, which makes me suspect the component linked between R54 and P5.

I noticed too on the schematics that there are two diodes next to where P5 is located but I cannot locate them on the amplifier or board.

I would appreciate it if any of you can help me with this.

Have included some photos which should help illustrate what I am (trying to) explain.

Thanks

snowman_al 21st Jul 2022 11:45 am

Re: Leak Stereo 30 Plus
 
1 Attachment(s)
Hi and welcome.
The component between P5 and R54 is a capacitor, just like C31.
It is 200pF and is marked as C37 on most diagrams. Unlikely to be a problem.


The diodes are not mounted on the board, they are on the output transistor heatsink, from memory. The connections are marked as capital letters and they are between C and J on the diagram. Follow the wiring.

Trevor 21st Jul 2022 11:52 am

Re: Leak Stereo 30 Plus
 
The schematic and pc board do not match
The schematic is for the germanium stereo 30 the pc is from a silicon 30 plus
Its always dangerous to swap the driver boards over as this can create more damage
I would first check the output transistors for shorts before going any further

snowman_al 21st Jul 2022 12:00 pm

Re: Leak Stereo 30 Plus
 
Hi Trevor,
The diagram posted by pcspike is poor quality, but is a 30+ diagram. You can just make out 2N3055 outputs and NPN emitter arrows.

Good advice not to swap the driver boards side to side though and a resistance / transistor junction test round the faulty channel in comparison to the good side will show possible faults for sure.

Pcspike 21st Jul 2022 12:46 pm

Re: Leak Stereo 30 Plus
 
Thanks for that, my next job will be searching for and testing those diodes.

Trevor 21st Jul 2022 12:46 pm

Re: Leak Stereo 30 Plus
 
Yes you are correct I have had my eyes worked on recently ( cataracts) and I don't think they are fully corrected as yet !
Still I would check the output devices first
Trev

G6ONEDave 21st Jul 2022 1:22 pm

Re: Leak Stereo 30 Plus
 
Not checked in the manual but the missing diodes might be mounted on the output transistor heatsink. Mounted there to limit the drive should the heatsink start to heat up, thus hopefully preventing thermal runaway.

Dave

Trevor 21st Jul 2022 1:34 pm

Re: Leak Stereo 30 Plus
 
These presets are of a very poor quality and are known to go open circuit at the wiper this will blow the fuse even if the transistors are ok check with a multi meter

Pcspike 24th Jul 2022 10:04 pm

Re: Leak Stereo 30 Plus
 
Quote:

Originally Posted by snowman_al (Post 1486320)
Hi and welcome.
The component between P5 and R54 is a capacitor, just like C31.
It is 200pF and is marked as C37 on most diagrams. Unlikely to be a problem.


The diodes are not mounted on the board, they are on the output transistor heatsink, from memory. The connections are marked as capital letters and they are between C and J on the diagram. Follow the wiring.

Thanks. Have found the diodes now and they measure ok. Re the 200pf capacitor is this type still available, if so where can i purchase?

Dave

Quote:

Originally Posted by G6ONEDave (Post 1486349)
Not checked in the manual but the missing diodes might be mounted on the output transistor heatsink. Mounted there to limit the drive should the heatsink start to heat up, thus hopefully preventing thermal runaway.

Dave

Thanks Dave, found them now....they were well hidden but measure ok

Quote:

Originally Posted by Trevor (Post 1486321)
The schematic and pc board do not match
The schematic is for the germanium stereo 30 the pc is from a silicon 30 plus
Its always dangerous to swap the driver boards over as this can create more damage
I would first check the output transistors for shorts before going any further

Hi Trevor, thanks. Will check them out, hopefully tomorrow

Quote:

Originally Posted by Trevor (Post 1486355)
These presets are of a very poor quality and are known to go open circuit at the wiper this will blow the fuse even if the transistors are ok check with a multi meter

Hi Trevor, have checked the pot (In circuit) and seem to measure ok. I agree that they could be of poor quality as well as being very old (but as old as me). I would like to replace them anyway, but looking at the modern ones they seem a lot smaller. Any idea were i could purchase somithing that might do the job?

Dave

Pcspike 25th Jul 2022 3:29 pm

Re: Leak Stereo 30 Plus
 
Quote:

Originally Posted by snowman_al (Post 1486320)
Hi and welcome.
The component between P5 and R54 is a capacitor, just like C31.
It is 200pF and is marked as C37 on most diagrams. Unlikely to be a problem.

I disconnected this capacitor today C37 and thought I would give it a try without it in place. I hooked up and played a CD before I switched on the amp so that a source was already in place. The results were good and bad. The good news is that it works as far as I could hear the music (and a low level hum) and it didn't blow a fuse! The bad news is that smoke billowed from the board. I switched off immediately, everything looked OK and found resistor R53 to be hot. It measured OK though.
Had a look on line for a replacement c37 at 200pf but was unsure if what I was looking at was correct, due mainly as I couldn't work out the correct voltage from the circuit diagram.

Would appreciate it you could tell me which I should go for.

Thanks

Sideband 25th Jul 2022 7:11 pm

Re: Leak Stereo 30 Plus
 
I would think that your C37 is OK. That low value suggests that it is there to prevent parasitic oscillations causing the amplifier to draw excess current and distort. Effectively it stops the amplifier becoming an HF oscillator. You won't hear the oscillation but it can cause distortion and the amplifier will draw excess current. Clearly the capacitor was doing its job so why change it? Just hope it hasn't caused any other damage running without it.

snowman_al 26th Jul 2022 8:27 am

Re: Leak Stereo 30 Plus
 
I assume you have a meter and can take resistance readings.
As you have C37 'free' (out of circuit) measure the resistance across it. It should be infinite and show O.L on the meter. Any resistance reading, low ohms to 100s of K ohms would be a fail.

As the whole unit has 48 volts on it, from the circuit diagram, so a 63 volt or 100 volt ceramic cap will be fine. (Example https://www.cricklewoodelectronics.c...Capacitor.html ) You will not get an original type today.

Perhaps it is time to build a 'dim bulb tester' / lamp limiter and take some voltage readings round the faulty side.

Pcspike 26th Jul 2022 12:24 pm

Re: Leak Stereo 30 Plus
 
Quote:

Originally Posted by Sideband (Post 1487368)
I would think that your C37 is OK. That low value suggests that it is there to prevent parasitic oscillations causing the amplifier to draw excess current and distort. Effectively it stops the amplifier becoming an HF oscillator. You won't hear the oscillation but it can cause distortion and the amplifier will draw excess current. Clearly the capacitor was doing its job so why change it? Just hope it hasn't caused any other damage running without it.

I have no reason to suggest that what you are saying is not correct, how could I, as I have no formal training, this is just my hobby, learning as I go basis thanks to the advice I am receiving here (thanks for your input by the way).
As you have already read, one channel is not working and blowing fuses when powered up. I have found that the two preamp boards are ok, I have tried both of them with the good amp board. I have also tried slotting the good amp board in the other channel slot (though I have since learned that this is not advisable) and found that by doing so the amp itself is working on both channels and that the fault is on this amp board. I have checked every component on it except for the cap directly connected to the P5 pot, so (in my mind), this was highlighted as the culprit, and as you may have seen in my reply to snowman_al, with this cap removed the amp did not blow a fuse and did work of a fashion. Iím going to replace this and see what it does if anything.
With that said, I would really appreciate your input as to how I move forward if the cap change as you suggest is not the fault.

Dave

Pcspike 26th Jul 2022 12:29 pm

Re: Leak Stereo 30 Plus
 
Quote:

Originally Posted by snowman_al (Post 1487453)
I assume you have a meter and can take resistance readings.
As you have C37 'free' (out of circuit) measure the resistance across it. It should be infinite and show O.L on the meter. Any resistance reading, low ohms to 100s of K ohms would be a fail.

As the whole unit has 48 volts on it, from the circuit diagram, so a 63 volt or 100 volt ceramic cap will be fine. (Example https://www.cricklewoodelectronics.c...Capacitor.html ) You will not get an original type today.

Perhaps it is time to build a 'dim bulb tester' / lamp limiter and take some voltage readings round the faulty side.

Thanks very much for that I really appreciate it, will get some ordered. Yes, I do have a meter that can take resistance readings, and as you say it reads OL a cross the cap. It also measures capacitance from 1 nf to 9999 uf but not pf. I have tried it and it just reads 1.
You could very well be right about dim bulb tester.. something else for me to learn??? though I am enjoying it.

majex45 26th Jul 2022 12:59 pm

Re: Leak Stereo 30 Plus
 
2 Attachment(s)
Are any of these of any use to the OP?
I know some are resistors but I think some are caps (some of the red ones are marked 1K) & others have a colour code.

Sideband 26th Jul 2022 1:35 pm

Re: Leak Stereo 30 Plus
 
They are all ceramic capacitors. 1k is simply another way of saying 1000pF. Others use a colour which essentially is the same as the resistor colour code. Yellow, Purple, Black for instance would be read as 47pF with the brown band as 1%. Sometimes the fourth band is a working voltage....brown 100V, red 200V. This is where you need a data book.

Pcspike 26th Jul 2022 1:58 pm

Re: Leak Stereo 30 Plus
 
Quote:

Originally Posted by Sideband (Post 1487530)
They are all ceramic capacitors. 1k is simply another way of saying 1000pF. Others use a colour which essentially is the same as the resistor colour code. Yellow, Purple, Black for instance would be read as 47pF with the brown band as 1%. Sometimes the fourth band is a working voltage....brown 100V, red 200V. This is where you need a data book.

This is valuable information, Iíve spent a lot of time online trying to figure out how these colours relate to the capacitors. I noticed on the other working board that it does say 200k on the cap, and couldnít make any sense of itÖnow I know, thanks:thumbsup:

Pcspike 26th Jul 2022 2:01 pm

Re: Leak Stereo 30 Plus
 
Quote:

Originally Posted by majex45 (Post 1487520)
Are any of these of any use to the OP?
I know some are resistors but I think some are caps (some of the red ones are marked 1K) & others have a colour code.

Had a close look and none seem to match. Thanks for your offer:thumbsup:

Sideband 26th Jul 2022 7:27 pm

Re: Leak Stereo 30 Plus
 
Some capacitor colour codes seem indecipherable unless you have a data sheet for the particular capacitor. It's also sometimes difficult to know which end to read the colours from. In these cases it helps if you have a test meter capable of reading low value capacitors...say from 10pF up to several hundred uF. You can also buy Chinese component testers that seem quite popular and not expensive. Check out eBay.

Be aware of different ways of writing the same value vis: 103, 10k, 10,000pF, 10nF .01uF, brown, black, orange or perhaps you'll see 102, 1000pF, 1k, 1nF, .001uF, brown, black, red. Then perhaps you might see 152, 1500pF, 1k5, 1n5, .0015uF, brown, green, red... It takes time to get used to all these variations!

102 for instance translates into 1 , 0 and two zero's. 103 translates into 1, 0, and three zero's. Lower case k is simply kilo or 1000 and lower case n is nanofarad.

Some very low value capacitors like 15pF might be marked n15. It pays to try and swat up on these variants.....these are only the most common.....

Note that three numbers can also be found on surface mounted resistors. 105 for instance would be 1 megohm (1 0 00000). On a capacitor it would be 1uF.

majex45 26th Jul 2022 8:37 pm

Re: Leak Stereo 30 Plus
 
Sorry I couldn't help. I'll keep looking through the bits & bobs.

Quote:

Originally Posted by Pcspike (Post 1487537)
Quote:

Originally Posted by majex45 (Post 1487520)
Are any of these of any use to the OP?
I know some are resistors but I think some are caps (some of the red ones are marked 1K) & others have a colour code.

Had a close look and none seem to match. Thanks for your offer:thumbsup:



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