Denon DRW 580 - various issues, possibly electronic

[TimS]

I have a Denon DRW 580 twin cassette deck with various issues. I've had it for c. 20 years and it was secondhand then.

The LH deck can be rather dull sounding, which I presume is an issue with the head, and I get the impression is solvable. Further cleaning, maybe alignment, and at the worst, a new head.

However there are also some intermittent control issues, and I'm wondering if these indicate a more show stopping issue with the electronics that may make pursing any fix for the above head issue not worthwhile:

• Random spontaneous stopping of tapes.
• Sometimes a brief fast forward occurs after the above random stopping, just for a few seconds.
• Sometimes pressing play results in a very brief fast forward, again just for a few seconds.
• Pressing play can cause the display to momentarily blank (the tape doesn't play when this happens). This is very intermittent, but when it occurs it can happen a few times together.
• Other very occasional erratic control behaviour e.g:
- the direction control 'works' in the display but then immediately changes back.
- whilst testing and trying to find a pattern to the intermittent behavour, I found that pressing irrelevant buttons while playing a tape (e.g. MPX) can sometimes cause a rewind or fast forward.

It's still a usable deck, but I don't want to address the LH head issue if the control problems are not something that can be realistically addressed. I'd be grateful for any opinions.

[SiriusHardware]

With such a diverse range of symptoms I think I would maybe consider a possible common cause for them all, such as bad regulation / high ripple on one or more of the power supply rails. This could lead to a power instability / power starvation problem where attempting to do anything which changes the power demand from low level to high level (ie, starting up the tape transport) could cause a momentary power shortage which could deprive the control section / display of power.

If you do go down that road usually the first place to start will be the electrolytic capacitors in the power supply, plus any which are placed 'locally' across supply rails. I'm assuming, possibly incorrectly, that you don't have an oscilloscope. If you have a capacitor test / ESR meter, test the existing ones one at a time - bad capacitors don't always show visual signs of being bad but of course if you do see any which have bulging tops or have clearly leaked electrolyte onto the PCB, those would be replace-on-sight.

Do you have a link to an online copy of the circuit diagram for your unit?

[SiriusHardware]

Found the service manual on Elektrotanya, but here for the time being is the power unit diagram. I've ringed the capacitors that I would check (in red).

The viewable version of the attachment will probably lose too much detail once the forum has auto-resized it so I have also attached a larger, more readable version of the same circuit diagram section as a .zip file.

[TimS]

Ta. I will take a look, possibly later in the week, and let you know what I find.

You're right - no oscilloscope. I do have a multimeter with a capacitance test facility.

-- Tim.

[Silicon]

Tape heads can become magnetised and it can alter the sound.

Do you have any equipment that could De-magnetize the heads?

[TimS]

Nothing untoward visible - see attached image.

A few of the caps have a slightly higher voltage rating than the circuit diagram. I presume it's wisest to go with these values if replacing.

I'll rumage in the loft for my multimeter tomorrow.

Silicon - no, I don't. But I don't want to start on the heads unless I can solve the control issues.

Ta.

-- Tim.