hifi engine

Hitachi d900 speed

Hello, how can i change the speed of my hitachi d900?



krokkor's picture

Re: Hitachi d900 speed

Hello,

in this model the speed controller is integrated inside the motor. So if you need to adjust the tape speed you've to adjust the trimmer that you can find directly on the motor. Watch for the motor's backplate and find the hole for the trimmer access. Use a little screwdriver (flat head, the model used for glasses screws) and insulate the metal head's bar with tape or heat shrinkable tube (this will prevent you'll short the trimmer with the metal motor's backplate). Insert the screwdriver in the backplate's hole and gently lock the screwdriver head on the trimmer; turn the trimmer in order to adjust the speed.

For a correct adjustement you need to play a test tape with 3khz or 3.15 Khz sample tone. Run the tape at least 20 minutes and then adjust the speed measuring the output frequency tone with a frequency meter.

If you're not equipped with those tools you can do a comparative adjustement with another tape deck. So record and audio sample file with the OK tape deck and then play this tape with the D900 tape deck while playing at the same time the original audio sample. If you can hear for both the audio (the sample file and the D900 tape previuosly recorded with the other tape deck) you will have just to eliminate the beating frequency adjusting the D900 motor's trimmer (the same way you adjust the pitch while you tune a guitar comparing for two strings on the same frequency).

Regards

Re: Hitachi d900 speed

hello again !!!
i have fixed to speed isue, but now i have another problem....

in the process of placing the board in its position, it touches somewhere in the chassis, and when I put it into operation ( power on ) activated the fast winding ( automatocaly ) without being able to stop it.

any idea ???

thank you.

krokkor's picture

Re: Hitachi d900 speed

Hello,

mecha operation are done in this model by solenoids activation (3 pcs. - FF/REW/PLAY). Maybe the solenoid related to FF is continuously active.
Pls. check if pulling off from its fixing points the control PCB or the PLUG PCB (keeping both PCBs wired) this fix the problem (in that case you loose some insulators in the screws fixing points that were mandatory in order to avoid short circuit of the PCB with the metal chassis). You've just to restore the correct insulation in that case. Search for unexpected contact points between the PCB and the metal chassis.
If this can't fix the problem look in the service manual (download it from this site) at Page 27 and find the FF solenoid (up left on the page). As you can see is connected by a couple of green colored wires to the PLUG PCB. Look at the 7 Pin connector of this PCB: from top to bottom 3rd and 4th wire are the FF solenoid connection. Remove one of the two wires from the 7 pins connectors in the correspondant place to FF solenoid, insulating this way the FF solenoid. Check now if the mecha stay in Stop position after the power on. If yes try to perform Play and REW and check for correct operation. If all is working (except for FF) maybe something on the Control PCB is shorted and keep the FF solenoid active.
Look now at page 22 (top right): you can see the PL-1 (FF solenoid) and his transistor driver Q60. Check this transistor if shorted and in affirmative case replace it (or exchange it with Q62 REW driver transistor for a test the FF's circuit); in case of replacement a medium power NPN transitor could replace Q60 without problem.
If the transistor is OK go back on the circuit checking for the logic state of his Base and the others components of the drive circuit.

Probably you've a short circuit on the PCB or the FF solenoid's driver transistor is shorted.
For a different kind of problem than the above listed ones you need to check the Control PCB but in that case you need some electronics competences.

Cheers

Re: Hitachi d900 speed

Hello and thank you very much for your time !!!

that the stop option does not work during the REW process, why do you say it happens?

thank you

krokkor's picture

Re: Hitachi d900 speed

Hi, if FF solenoid stays active there are no stop operation you can perform in order to stop the FF.
Check the solenoid as described in my last post.

Cheers

Re: Hitachi d900 speed

hello , and thank you very much for your support !!!
I change one transistor ( Q62 because the problem was at REW action) and now when i push the REW or FF button, stays ''on'' ( green led ) , but the solenoid not actived. Play mode is ok. Stop is ok.
When the deck is turned on, sounds something ( like somethin gonna actived but not happend at the end..)

Now i try to change and other transistors ( Q60 e.t.c.) and we see....

I want to say a BIG THANK YOU !!!!!

krokkor's picture

Re: Hitachi d900 speed

Hi Andreas,
Check anyway the transistor you've replaced if was shorted 'cause in negative case the problem came from the logic control or another component on the Control PCB. If you don't have a multimeter for test the transistor you can simply exchange this transistor with another similar solenoids driver on the control PCB (if shorted the fault will be transfer on the FF or Play solenoid).

Cheers

Krokkor

Re: Hitachi d900 speed

thank you very very much !!!!!!!