The Sinclair QL Forum

Interested in 4 please.

Hi Dave

Dave wrote:The other obscure but common problem I saw was that two of the microdrive units had erase tab detect switches that contained enough tarnish to cause poor contact. Both poor contacts were between pins 1 and 3, which is the position that enables the erase circuit. This caused improper erase function.

I have noted that a couple of my MDV units can read happily, but always fail to FORMAT or write to the same tape. Of course, head or ULA are still in the frame, but if the WP switches themselves could be also in the frame as you suggest, how straightforward is it to open them up and polish-off any observed tarnish? How would you measure the impact of such switches - a DC resistance measurement across the (closed) contacts, perhaps?

Is that a valid troubleshooting step in your view?

What I did was just operate the switch repeatedly a couple of hundred times while bathing it in contact cleaner. That doesn't get the crud out of the case, but it does move it around to where the switch makes contact properly again. It's a very standard switch and quite easy to find replacements.

Hi Dave

OK. Before blindly replacing a switch, can the additional resistance of tarnished contacts be measured externally?

Yes.

Generally, it's the write allow position that has the issues. That's pins 1 and 3.

Thanks Dave. I'll investigate my couple of FORMAT duffers and see what I measure.

Long time since I've posted on here, but I would be interested in 1 or 2.... Just recently blown the dust off my QL to have another go with it!

Cheers,

Simon

Cool. I'll be ordering the microdrive boards as part of the panel for the Issue 8. That way they get to be 4 layer boards at little extra cost as they're in "free space"...

I can get the combo ERP heads from a specialty company

Hi Dave,
I am so currious about R/W head drop in replacement, as I thought it
impossible.

Slightly off-topic, while I was looking for an audio device with continuous
loop, I came accross STEREO-8 system. Developed by Lear Jet aircraft
company. It used 1/4 inch tape with 8 tracks. It was fitted in stereo
car playback systems in the 1960's or so. Generally it predates compact
cassettes as we know today.
Can you please share specification, pictures, of ERP combo head
replacement you had sourced?

Many thanks
Tomas

Unfortunately, the company that made the heads went out of business a long time ago. The company that took over their stock cannot find the items they thought they had. Also, they want an incredible sum per head if they could find them. It looks like re-using existing microdrive heads is the only path open to us.

They wanted $60 per head and thought they had "maybe a dozen." That does seem to be in line with the normal pricing for new heads of that era.

I'm continuing with the project, but it is a rainy day project when I'm not able to make progress on more urgent projects.