Topic: onkyo stereo amp.

[grcamna2]

Hi scottly,
I'd like to ask you a question about my Hitachi TRK-7700H mid 80's boombox.I can turn it on and everything works and after about 20mins.(+ or -) of operation(depends)everything dies like as if I turned off the power;if I wait about an hr.+ it'll allow me to turn it back on..kind of like 'a time out when it feels like it' type operation.I purchased a factory service manual for it but I'm not an electronics guy,I've repaired mechs. on lot's of tape players but that's about it.I have it in my closet until I feel like I can come up w/ a plan of action.Can you give me any clues what I might like to check ?

                                  hey Thanks, Bill

[scottly]

Bill, are you using it on AC when it fails? Does it act the same with a fresh set of batteries?

[BobbyR]

Hi scottly,
I'd like to ask you a question about my Hitachi TRK-7700H mid 80's boombox.I can turn it on and everything works and after about 20mins.(+ or -) of operation(depends)everything dies like as if I turned off the power;if I wait about an hr.+ it'll allow me to turn it back on..kind of like 'a time out when it feels like it' type operation.I purchased a factory service manual for it but I'm not an electronics guy,I've repaired mechs. on lot's of tape players but that's about it.I have it in my closet until I feel like I can come up w/ a plan of action.Can you give me any clues what I might like to check ?

                                  hey Thanks, Bill

It is most likely a component that fails when it reaches a certain temperature. This is usually diagnosed by using a freezing spray and spray one component at a time until the unit comes back to life. People have also taken a small spoon or piece of Aluminum that has been put in a freezer for a while and touch each component at a time. It usually means freezing several spoons at a time because they warm up fast.
Once you find the part that is failing, you have to replace it. If you have the proper soldering pen and some skill you can do it.
 

[grcamna2]

Bill, are you using it on AC when it fails? Does it act the same with a fresh set of batteries?

I haven't tried it w/ 8 D-cells yet..you think possibly AC to DC power transformer ?
I'll do that test w/ 8 batteries(or how about the 'DC 12vts.in' jack?) first before checking further.

ps: I tried typing '8' w/ ')' too close together and it made this  guy  ,sorry

[grcamna2]

Hi scottly,
I'd like to ask you a question about my Hitachi TRK-7700H mid 80's boombox.I can turn it on and everything works and after about 20mins.(+ or -) of operation(depends)everything dies like as if I turned off the power;if I wait about an hr.+ it'll allow me to turn it back on..kind of like 'a time out when it feels like it' type operation.I purchased a factory service manual for it but I'm not an electronics guy,I've repaired mechs. on lot's of tape players but that's about it.I have it in my closet until I feel like I can come up w/ a plan of action.Can you give me any clues what I might like to check ?

                                  hey Thanks, Bill

It is most likely a component that fails when it reaches a certain temperature. This is usually diagnosed by using a freezing spray and spray one component at a time until the unit comes back to life. People have also taken a small spoon or piece of Aluminum that has been put in a freezer for a while and touch each component at a time. It usually means freezing several spoons at a time because they warm up fast.
Once you find the part that is failing, you have to replace it. If you have the proper soldering pen and some skill you can do it.
 

Thanks for the tip BobbyR;you mean do that after the unit shuts down ?

[grcamna2]

Dave500,
Should I start another thread for asking these questions ?

[BobbyR]

Hi scottly,
I'd like to ask you a question about my Hitachi TRK-7700H mid 80's boombox.I can turn it on and everything works and after about 20mins.(+ or -) of operation(depends)everything dies like as if I turned off the power;if I wait about an hr.+ it'll allow me to turn it back on..kind of like 'a time out when it feels like it' type operation.I purchased a factory service manual for it but I'm not an electronics guy,I've repaired mechs. on lot's of tape players but that's about it.I have it in my closet until I feel like I can come up w/ a plan of action.Can you give me any clues what I might like to check ?

                                  hey Thanks, Bill

It is most likely a component that fails when it reaches a certain temperature. This is usually diagnosed by using a freezing spray and spray one component at a time until the unit comes back to life. People have also taken a small spoon or piece of Aluminum that has been put in a freezer for a while and touch each component at a time. It usually means freezing several spoons at a time because they warm up fast.
Once you find the part that is failing, you have to replace it. If you have the proper soldering pen and some skill you can do it.
 

Thanks for the tip BobbyR;you mean do that after the unit shuts down ?

Yes, you want to bring that part back to the temp it will work at. Run it till it quits and then you start checking.

[dave500]

Dave500,
Should I start another thread for asking these questions ?

naw keep it here man,all good,that way were on the same wave length,unless we start a hi fi section only?

[grcamna2]

Dave500,
Should I start another thread for asking these questions ?

naw keep it here man,all good,that way were on the same wave length,unless we start a hi fi section only?

Love it ! 

[dave500]

ha ha no worries,thanks for asking.

[strynboen]

a littel film for the heigh tech sektion on sohc forum...

i got 3 scoops for free..this littel and a 2 big 100mhz..have tested it on some 27 mhz..give nice resultats.

..but mine idea vas to test cdi units for delayed/forced ignision timing..by use a common start/trig, point at 2 canals.. at same timeand se the differens fire point..

but im a machinist ..not elektronist...

[scottly]

Bill, are you using it on AC when it fails? Does it act the same with a fresh set of batteries?

I haven't tried it w/ 8 D-cells yet..you think possibly AC to DC power transformer ?
I'll do that test w/ 8 batteries(or how about the 'DC 12vts.in' jack?) first before checking further.

ps: I tried typing '8' w/ ')' too close together and it made this  guy  ,sorry

Yes, I was thinking of the AC to DC power transformer. I worked on a Fisher amp once that had a thermal switch nested in the transformer windings that had failed...

[grcamna2]

ok scottly thanks

[grcamna2]

Bill, are you using it on AC when it fails? Does it act the same with a fresh set of batteries?

I haven't tried it w/ 8 D-cells yet..you think possibly AC to DC power transformer ?
I'll do that test w/ 8 batteries(or how about the 'DC 12vts.in' jack?) first before checking further.

ps: I tried typing '8' w/ ')' too close together and it made this  guy  ,sorry

Yes, I was thinking of the AC to DC power transformer. I worked on a Fisher amp once that had a thermal switch nested in the transformer windings that had failed...

scottly,
My Hitachi TRK-7700H boombox also has a 'DC 12vt. in' jack in the back of of it and I want to ask if plugging in to that and powering it up there would also defeat using the AC/DC power supply and be a good way to test to see if the operation will continue? I know you mentioned installing (8  D-cell) batteries and testing the unit that way.
                    thanks 

[scottly]

Yeah, you can plug a 12 volt DC supply into that jack for testing. Make sure the polarity is correct.

[754]

Stynboen,  i did not know you were a machinist.... Very cool..

[grcamna2]

Yeah, you can plug a 12 volt DC supply into that jack for testing. Make sure the polarity is correct.

I was wrong on that plug on my TRK-7700H;I had one on a TRK-9900H a few years back that I sold.. 
I have six(old) D-cells w/ varying voltages from 13.35 all the way up to 14.43 volts(and I can get 2 new D-cells to make 8 total)... I also have an AC-DC adapter power cord that I plug into the wall and get DC volts from 1.5-12 volts & it gives out 300mA max(this boombox pulls 18wt. max).. I think this boombox is old(mid 80's)enough to just hook up that 300mA AC-DC power cord set at 12 vts.(or my 12N12A-4A-1 cycle battery)to my battery box contacts in the back so it powers from them and just run it for hours until I've determined what the 'shutting down' problem is.
scottly,what option do you think would be my best one for long DC operation ?

[grcamna2]

I know that a constant steady power source is important & I think I should hook up my 12N12A-4A-1 to the battery box contacts and just keep the battery charged while I test the boombox,it's cheaper  than D-cell batteries

[dave500]

might not show up on D cells or 12 volt hook up but only mains supply?if so you know what it is then to a degree?

[grcamna2]

Bill, are you using it on AC when it fails? Does it act the same with a fresh set of batteries?

Dave,I want to do what he suggests to bypass the possible defective  AC-DC transformer power supply.This boombox also has a multi-voltage rotary switch on the back for switching from 115 to higher voltages as other countries would normally run 220vts. AC,etc.;the USA uses 115 vts. AC in all it's receptacles.I wonder if that multi voltage switch could be a problem..?
 I haven't opened it up yet but would like to try the DC operation only which scottly suggested above first;the PC board on this boombox is low voltage DC power.
I want to run it strictly on DC-in operation so I can see whether it shuts down as it was while running on the AC-in w/ my power cord, & if it doesn't shut down at all then it could possibly be my internal AC-DC transformer power supply?...

Sometimes it'll run for a while(a couple hrs.)on the AC power cord w/o a problem.

I'm just asking scottly about a good DC power in,either D-cells or my M/C battery,etc. ? I'd have to buy 8 new D-cells and that's about $14 here so if I could rather put that $ into parts later...

[scottly]

Yes, you can run it off a bike battery, if you can find an easy way to connect wires to the boom-box battery terminals. I wouldn't use a charger on the battery while playing the radio. Don't over-think this; some of these units aren't worth the cost of repairs, even if you can find direct replacement parts.
One time a regular customer came into Dad's shop, looking to have a transistor radio repaired after it had been "slightly" crushed in an LP record press. I had break the news to him that his beloved radio was totally FUBAR, and would cost 3 times as much to repair as a brand new, better quality radio.

[grcamna2]

got it ok scottly.
This boombox is in Excellent vintage shape and hasn't been abused;i'm going to take a pic of it soon.I've been running it on AC-in now for 1.5 hrs. at a time after having 'spun the dial' on the AC voltage regulator multi input switch as a prelude to the testing,so I haven't done a DC-only test just yet because it hasn't messed-up on AC test yet...
 I should open it up and clean all the switches and power carrying contacts w/ Deoxit.

[RAFster122s]

Gee, learn more about skills people have ever day. Anyone mess with tubes anymore?

Discovered Mom's Aiwa mini stereo isn't playing but very faintly out of the right channel a few days ago. Asked her when that happened and she didn't know as she had not detected it.

The speakers are nested against the main body as it is configured now like an oversized boom box.
I have not opened it yet.
Hopefully it will have a logical layout and clearly label the board. I am guessing it has a blown transistor (or the R ch of the IC chip) for that channel of the amplifier section of the circuit. 
Speaker is fine and it has clear sound if you turn up the volume after disconnecting the left channel, thus my presumption of amp section of the circuit.
 
She uses it a lot and sometimes uses cassette tapes,  so replacing it with a modern device probably won't work.

[Duke McDukiedook]

I have a few tube amps, preamps and a tuner...
I need to recap a few of them if I ever get the time.

[strynboen]

you can get tubes in russia..a frend got a box full ,of the most super made for planes and misils in erly 70"..they are on opend marked for lov preises..and heigh kvality