UK Vintage Radio Repair and Restoration Discussion Forum

UK Vintage Radio Repair and Restoration Discussion Forum (https://www.vintage-radio.net/forum/index.php)
-   Vintage Tape (Audio), Cassette, Wire and Magnetic Disc Recorders and Players (https://www.vintage-radio.net/forum/forumdisplay.php?f=35)
-   -   Nearly silent output from vantone reel to reel machine (https://www.vintage-radio.net/forum/showthread.php?t=154878)

Cont3mplation 13th Mar 2019 10:46 pm

Nearly silent output from vantone reel to reel machine
 
Recently picked up this reel to reel recorder from eBay:

https://picclick.co.uk/Retro-Vintage...613906739.html

I'm aware this is almost little more than a toy, but I wanted a small portable reel to reel to mess with on the cheap, so this seemed perfect. On arriving I cleaned it off and got it running pretty good, however I've found that both the internal speaker and headphones play the audio so quiet that it's barely perceptible, and it took me some intense listening to hear anything but static. However the audio does seem to be there, so I'm wondering, what could cause it to be this quiet? I cleaned off the heads and I checked it wasn't the tape, and on looking inside it I don't see any huge issue with any of the caps or components there. Is there something that would cause this to look for? Any help appreciated, thanks

Edit: there's also what seems to be a grounding wire(?) Connected to the headphone and mic jacks, the green and black cable visible in the photos. I'm using batteries so I doubt this is the issue but I'm not that well versed in hifi so might be part of the problem, I'm not sure

ben 13th Mar 2019 11:08 pm

Re: Nearly silent output from vantone reel to reel machine
 
could be:
-dirty volume control pot
-dirty rec-pb mode switch contacts
-leaky output or driver transistor
-faulty capacitor in amp or preamp

I have had all these cause this problem before.

AC/HL 14th Mar 2019 11:50 am

Re: Nearly silent output from vantone reel to reel machine
 
1 Attachment(s)
That link is dead, is this the Vantone in question?

Cont3mplation 14th Mar 2019 5:33 pm

Re: Nearly silent output from vantone reel to reel machine
 
Yup that's the one, and am going to try to get into it and do some more cleaning and testing soon, will see if it could be any of those

Cont3mplation 14th Mar 2019 7:11 pm

Re: Nearly silent output from vantone reel to reel machine
 
Having looked inside I don't see any damaged capacitors (will link to imgur post asap) and I don't actually see any transistors anywhere within the machine which strikes me as odd. But will get photos up as maybe I'm missing something here

Cont3mplation 14th Mar 2019 10:04 pm

Re: Nearly silent output from vantone reel to reel machine
 
http://imgur.com/gallery/I0vCK1J
Some photos of the circuits and internals

jamesperrett 14th Mar 2019 11:18 pm

Re: Nearly silent output from vantone reel to reel machine
 
I think I counted 5 transistors on the circuit board - they're the devices in metal cans. The head also looks a bit dirty - this would be enough to stop it recording and make any previously recorded tapes sound pretty dull.

What happens when you touch the head connections while the machine is playing a tape? Do you hear a buzz?

Cont3mplation 16th Mar 2019 8:43 pm

Re: Nearly silent output from vantone reel to reel machine
 
Ah yeah, forgot for a minute their transistors aren't all encased in black, but when I try touching the head or the head pins while playing back there seems to be no reaction, or not one loud enough to be heard over the motor regardless of volume settings

Cont3mplation 16th Mar 2019 8:43 pm

Re: Nearly silent output from vantone reel to reel machine
 
I tried shorting the pins of the volume control while it played but that seemed to make no difference either, and for the record I'm pretty much brand new to reel to reel and vintage audio as a whole so apologies if I'm a bit useless when it comes to it

Chris55000 19th Mar 2019 2:28 am

Re: Nearly silent output from vantone reel to reel machine
 
Hi!

What fault finding equipment do you have?

You'll need a good quality digital multimeter and a small a.f. oscillator to diagnose this type of fault – you can get little kits/modules of a.f. sources for as little as 99p (free postage!) online!

You also need one of those little Chinese LCR T4 Testers for testing the passive components, as well.

Very low volume on this type of amplifier is commonly caused by degradation failure of the germanium amplifier transistors, particularly if somebody has accidentally reversed the polarity of the battery supply in the past – this will destroy them, but not always immediately, and power supply reversal can cause failure of a peculiar type where d.c. voltage readings test very close to normal but the transistors are incapable of correctly amplifying – I have personally had cases of this!

The first thing to do is to try and obtain the service–sheet or circuit diagram of the player's amplifier board – it's a standard transformer–coupled class B design about 250mW output with two additional transistors for tape head preamplification/frequency correction

If you can manage to read off the numbers on the metal transistor cans I'll give you a few typical voltage readings to expect!

Chris Williams

Cont3mplation 20th Mar 2019 9:41 pm

Re: Nearly silent output from vantone reel to reel machine
 
Hi, thanks for the detailed reply, I have a pretty decent digital multimeter but that's about the extent of it, if you'd be willing to link some of the others that'd be amazing, and will try to find the data sheets

Cont3mplation 20th Mar 2019 9:45 pm

Re: Nearly silent output from vantone reel to reel machine
 
Have had a look and from what I can see this thread is essentially one of the only things ever posted online for this recorder, not a single diagram or manual or even reference to be found. Is there any generic data sheet that'd work for the purposes of testing? Thanks

Cont3mplation 12th May 2019 9:28 pm

Re: Nearly silent output from vantone reel to reel machine
 
So despite this thread now being a good bit old will leave a final message here if anyone encounters the same issue. After leaving it for months I finally came back to this problem and found that you can test capacitors using a normal multimeter set to resistance measurement. When you test a cap that is working normally, the resistance will start from a value depending on the voltage and till then increase as the capacitor drains. Used this to test all the caps on the amplifier circuit and whaddaya know I found one that wasn't working correctly. Shorting across the pads with some wire I found it now made sound, quiet sound at that but sound nonetheless. I replaced this cap with a similarly sized one I had and went on to test the other capacitors on the same line. Replaced them too and at the end it now plays back audio relatively fine. Some crackling here and there but I'll certainly take that over nothing. tl;dr: caps were dead and replacing them fixed the issue. Hope this helps anyone who finds a similar issue at some point in the future.

Refugee 12th May 2019 11:49 pm

Re: Nearly silent output from vantone reel to reel machine
 
That board looks like the ones in DC bias shoe-box compact cassette recorders.
Those capacitors are polarity sensitive and if you guessed at the value for the replacement part you might get an improvement with the same value.
Well done for getting this far.

ricard 13th May 2019 2:28 pm

Re: Nearly silent output from vantone reel to reel machine
 
Yes, I think there were lots of these styles of machines manufactured in Japan in the late 1960s under various brand names. I recognized the head arrangement and some other internal parts from a machine I once had labeled the 'Granada 207'. Fairly well built, but the DC bias system was a letdown as all recordings had that typical DC bias rumbling noise in the background. Given that there are 5 transistors in the amp circuit, it's a pity they didn't invest in the additional switching and HF coil needed to convert the output stage to a bias oscillator in record mode which would have improved matters significantly, even when retaining the permanent magnet erase head.


All times are GMT +1. The time now is 7:52 am.

Powered by vBulletin®
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
Copyright ©2002 - 2019, Paul Stenning.