Hitachi TRK 8190 - no stereo reception in FM

[Superduper]

You obviously have some over-current situation going on. Might be intermittent but whatever, you need to research further. If have the schematic, you can research downstream components from Q502 if that's what's blowing. Either that or you are installing counterfeit substandard parts. If you got them off eBay, that is a very good possibility. You can connect a DMM in amp mode, and splice the meter between the emitter junction, monitor the current draw. That regulator has a rated collector current of 2.5 amps but it's collector power dissipation is only 3/4 of a watt. If you think that the quality of the transistor is an issue, and you are in the USA, I have some 2SD2023 in stock and TIP29C in stock. The C1162 has improved nominal collector current of 2.5 vs 1, but when installed on a heatsink, the 29C has the same 3A rating. More importantly, it can handle 2 watts without heatsink and 30w with a proper one. Or the D2023 which is probably a better choice at a 3A collector current but 40 watt collector dissipation vs 3/4 on the original. Both the TIP29c and D2023 have a reverse lead pattern though. 1162 is EBC whereas TIP29c and D2023 is CBE. That means that the transistor will be mounted backwards (reverse/flipped).

 

[beamrider]

Thanks - I've got the heatsink back on now. I'm in the UK so, If it blows again I'll look at sourcing some of those instead. I'll also check the current draw on Q502 as you suggest.

 

[beamrider]

So after much experimentation made another discovery. The unit works fine UNTIL I attempt to press REW whilst playing a tape (REW works fine in isolation). After this Q502 blows. I hoped the leaf switch on the REW button might have had a pin touching ground or something but alas not the case.

 

[Superduper]

The primary difference between the CUE and RW function is that cue activates the music search feature. Unless something in the cue circuit is amiss like a shorted IC or a short in the solenoid or excessive current draw, it shouldn't make any difference. Does it only happen with Rev cue or also with Fwd cue? The other problem with this theory is that while the solenoid is a high current device, it isn't powered by Q502. However, the Play, FF and RW switches do pull from Q502. You may want to check C456 (1000uf so it is probably a large tall skinny one) and R717 to see if they are shorted. You may also want to check RW switch to see if it triggers ground for some reason by probing (with ohmmeter in Rx1 setting or autorange), one lead at R490 and the other at ground. With unit unplugged, operate RW switch. Ground should not be triggered. If you are getting ~1k, check again at the other R490 lead. Alternately instead of checking at R490, you can check directly at the RW switch if that is easier. However do not just "look" at it. Put a meter on it and check it against gnd when operated. Regardless, either you have a short or shorted component, or you are using subpar components for Q502. The only way that regulator blows normally is in an overcurrent condition.

 

[beamrider]

Thanks, will try those suggestions. Yes, it only happens with Play+REW at the same time, no other combos.

 

[beamrider]

So replaced everything Q502 and ZD502 again to get it working. Then checked out your kind suggestions and found that pressing Play+RW did cause Q502 to be dragged down to ground. I removed the leaf switch board and found what I think is the culprit. The black plastic insulator appears to be missing from the bottom of the RW leaf switch and is being forced against the metal keypress. Closing the leaf switch alone does not trigger the fault, it has to be closed and simultaneously touching ground and the play button held down.

Will fix it tomorrow by gluing a small piece of replacement plastic on it and report back.

 

[beamrider]

so pleased to report electrically the unit seems to finally be stable. Put back the all boards and now working on the tape mechanism.

I replaced a rubber tyre as forward wind was weak. Also I replaced the pinch roller as it was highly glazed.

In trying to reduce the high wow and flutter (~0.7) I noticed tapes wouldn't rewind . On inspection, seems to be an issue with the tape path during play as I hear tape crinkling then then as it's ending up misaligned on the take-up spindle causing binding.

 

[beamrider]

OK, I've fixed that - it seems the replacement pinch roller was slightly convex causing the tape to skew off to one side so I've replaced it with another one from a different supplier.

I still have a high wow and flutter though of around 0.6%. I 'm going to oil the motor shaft and recheck all the belts and pulleys.

 

[beamrider]

Got the wow and flutter down to between 0.25 and 0.65%, I believe 0.2% is the supposed minimum acceptable level. Unfortunately the indicated white pully seems to be slightly deformed which is inducing an oscillation on the motor so I guess that's as good as I'm going to get it without having a bespoke replacement machined up in brass?

 

[Superduper]

It's a boombox. Not a nak.

 

[beamrider]

True, but I think the original spec was fairly good around 0.06%. Anyway I got it down to 0.2% eventually.

 

[beamrider]

So finally got this restoration complete -

Turned out to be particularly challenging one for a first restore.

In summary, I performed a belt change and noticed the stereo FM light was not on. In trying to fix this I found it to be a faulty decoder IC, replaced this but also found a transistor Q502 was faulty. I replaced this and put it back together only to discover the radio wouldn't play (this turned out to be due to incorrect wire color labels on the PCB - thanks to James Bennet for his you-tube video (vEwS5TFzwQw) . I went through several more iterations of replacing Q502 and the co-located zenner diode ZD-502 to have it fail on final reassembly and testing. This turned out to be a missing leaf switch insulator that I didn't notice on the first few inspections and only manifest when testing the DPRS system with play+rewind and causing the transistor to blow. Another issue was that the constant opening up and reassembling broke the fragile ribbon cables so I had to replace those with JST connectors and cables. Another issue was the function switch causing a voltage drop even after cleaning so I replaced that also Finally I had issues with the tape mechanism. Forward wind didn't work so had to replace a tire and also replaced the pinch roller which then caused tape skewing off to one side (bad replacement roller) and then some bad wow and flutter which I eventually got acceptable after multiple cleaning attempts although its not to spec. So finally it's working and I can have my weekends back...

Thanks to all the help received on here, in particular SuperDuper without which I wouldn't have been able to complete this.

I have another one to restore but I think I'll save that for a good while

 

[floyd]

Good work !.
Glad it got sorted out.
I love this model boombox.