Tascam Porta One

[Enzo]

Hi

Really, it is better to start a new thread for yours instead of tacking onto the end of a real old thread.

google for tape recorder belts and find various sources. If there is a lookup that includes your model then great. otherwise, take your belt off and measure it. It may be stretched out, but it stops stretching as soon as it loses grip. So subtract a couple millimeters from your circumference reading.

Some examples:

http://www.cassettedrivebelts.com/

https://www.turntableneedles.com/Rub...cks_Turntables

https://www.vintage-electronics.net/...-belt-kit.aspx

[The Dude]

If you just need the capstan (flywheel) belt, it's Teac part number 5760646100. The PRB cross is FRW10.1.

https://marvac.com/products/prb-frw-...-drive-frw10-1

If you need an entire kit, they are available several places. Just search porta one belt kit.

[cbradshw]

Hello Brad1, I too have a Porta One that my wife had when I met her. Over the years it worked just fine and we now wish to use it for some basic multi-track music creation.
Upon firing it up everything lights up fine. The first noticed issue was that the tape transport was stuck in the Play engagement mode. When pressing any of the button except stop I notice that the lights dim and the power button goes into a blinking mode, almost as if to be undervoltage or over drain.
I do have a very good ability at electronics repair so I viewed YouTube videos and opened the unit up. No real issues with dust but I thought that perhaps the deck mechanism could do with lubrication. It was a little gummy but nothing too bad.
Upon trying to put it into play mode and manually turning the flywheel the transport does mode into place. But more alarming was the slight familiar smell of a hot component. Immediately I powered off to try and find where this was coming from.

It turns out the Q1 transistor is indeed getting hot and at one point was smoking a little. I intend to follow your parts list that you described above and get them off of Digikey.
I just wanted to share my experience with you to ask of any second thoughts you may have about the unit.

Feel free to ask more specific questions.
Cheers,
Christopher

[Chuck H]

Well Brad probably already solved any problems he was willing to address seven years ago. And it seems Bucko just needed a belt and that was identified for him to the manufacturers part number. But on YOUR issue...

Just so you know, it's not enough to just replace that transistor that's getting hot. The reason it's getting hot is likely something other than the transistor itself. Probably an electrolytic type capacitor. You should look for this and any potential damage to resistors in the circuits associated with that transistor and otherwise try to identify the actual cause. A bad electrolytic cap in it's typical failure mode could be causing problems with that transistors power supply or bias condition and is the most likely component to fail at that units age. Then do like I would and just replace all the electrolytic caps in the entire unit. They don't last forever and those are something like thirty years old.

[cbradshw]

Thanks Chuck for the reply on this old thread. Thank you also for the very insightful knowledge of how the surrounding components are apt to be causing a strain on the main Q1 transistor. Indeed, I shall now be ordering items as listed by Brad. One immediate issue is I see that the Q1 transistor is now obsolete. I'll need to carefully check all the specs of my replacement transistor so that it matches.
Indeed, for a unit 30 years old failures are not a surprise. Incidentally, I drive a '92 Buick Riviera and it's an excellent vehicle, sure a brake line went out on me on my way to work one day but as long as a person is willing to fix things, quality products can run a bit longer. You know, a friend mentioned to me the capacitor plaque topic that appeared in electronics about 10 years ago. Such tiny things with a huge impact.

Cheers,
Christopher

[Enzo]

I forget which model now, but Porta1 was popular back when. But there was one transistor in the power supply regulator circuit, that screwed to the tape transport frame as a heat sink. There was a screw through its hole on the rear edge. ANy chance this applies to you? If that transistor is not screwed to its heat sink, it will overheat.

[cbradshw]

Thanks for that insight!

Thank you Enzo for providing insight about the Porta One. The particular transistor that was indeed hot Q1 does not have a mountable tab design to it but I will keep an eye out for other transistors that perhaps do have tab mounting. Sometimes the thermal coupling paste dries out and goes bad.

I am about to start up an order on Mouser. I did want to go with Digikey but the Q1 transistor calls for 1W dissipation, the best Digikey could provide was 800mW. I'll take some sweet time to try and get the perfect replacements.
If I do get this puppy all fixed and working I'll certainly post to this thread and also create a web page about it on my personal Project's Bin website. Even if it doesn't work I'll still post here to help anyone that may visit.
Many many thanks for your help on this topic! I feel we're a rare breed of people to be willing to get into boards and talk shop.
Christopher

[g1]

I think the regulator Enzo referred to is U1.
Q1 is the regulator for the motor (2SD1207S).
With the heads not coming up properly and Q1 overheating, there is a bit of a chicken or egg scenario. The heads may not be coming up because the motor is not getting correct power, or the motor may be bad or gears in the mechanism are sticking and the extra load on the motor is making Q1 overheat.
I certainly did a lot more work on the gear assy's (gear replacement or clean/re-lube) than Q1 replacement. But motor replacement was probably more common than either of those 2 issues.

[Enzo]

No, I am just remembering some other unit. The transistor was a 2SC916 or something like that. Ignore it, I am leading us down a false path it seems.

[cbradshw]

SUCCESS! After swapping out the six components with the new ones the deck is coming up and motor working. It seemed like it took a little coaxing to get things working again. There really wasn't much lint/dust in the system there but I did lubricate some areas. My first goal was to get the motor running as so I removed the two belts from the motor just to allow it to spin freely. Then I hooked the belt back up and things got working again. I plan to do some test recording soon and eventually will post a proper update about my experience. It seems that the capacitor C1: 647-UVZ1C101MDD Capacitor 16V,100uF is the one that went bad. The Q1 transistor appeared to be showing fine in my post-surgery survey. Just wanted to pass this happy news on for visitor to the site. More to come in the future.
Cheers, Christopher

[cbradshw]

OK, I have now made a dedicated page to my projects website to show others this fix and hopefully help those that find themselves in the same problem:
http://christopherbradshaw.net/The_P.../projects.html

Thanks again to you all for your excellent support and I am so glad to have the unit working again. I did some test recordings on the tracks and it behaves like a proud unit should.

In my tests the resistors checked out fine and the two large caps were fine as well. the C1 cap was not providing capacitance, in fact it was showing conductivity, so that could explain the strain dealt to the Q1 transistor which was showing proper test behavior.

Again all the best to you!
Christopher

[Chuck H]

Five posts in and already adding to the knowledge base of the forum and linking details for others.

I like this guy