348 Speedo Burned Internals

So the "low hanging fruit" at this point is to replace the large IC?

I see what you mean about the smaller one. It was made by Harris Semiconductor, which has sold of its designs to a couple of companies and I can't find any datasheet for that number.

Thanks!

///Mike

 

Not to my knowledge, at least not in the speedo wiring (someone used a couple to tap into the wiring for the central lock switch when they installed an alarm ). I'm 99.9% certain those didn't come from the factory. Where did you find them and was anything plugged into them? Any evidence that the car ever had an aftermarket cruise control installed?

 

No way of telling for certain, but I'd bet decent money that the 92693 would cross to another part that's more readily available *if* we could find a cross-reference for Harris numbers. Before the interwebZ we had these great manuals that would cross almost any semiconductor. I'm now kicking myself for throwing mine out over the years. But I figured the old-school electronic supply house where I used to get them would still have copies from the old days, so I took a trip down there today. No such luck, although the counter guy agreed with me that we need an old ECG manual like this one: ECG 212P Semiconductors Master Replacement Guide Electronics Manual Philips

I tried searching from that angle, but got nowhere. If you have any friends who are old-school electronics hobbyists or have an old-school local supplier, it it'd be worth a shot to see if they still have one of those books around (hopefully one a little later than the one on eBay).

In the meantime, I sent an inquiry to the people at the first link you posted. I'll let you know what happens.

Thanks for the links!

 

I'll take a look at mine later when I'm where the car is, but I can't imagine that those are stock. They weren't connected to anything? If not, that still doesn't tell you where the voltage is coming from. Another odd thing is that there's one tap on a signal wire and one tap on what I believe is the backlighting wire. Then again, whoever did that wasn't the sharpest tool in the shed, so maybe they were tapping into wires at random.

Hmmm... I wonder if that's what happened. Any chance someone looking for a hot source tapped into the speedo wire because it's red, and now it's getting backfed voltage from the stereo installation? Just a thought...

 

I changed my search parameters on eBay and wound up finding a couple of '91 ECG manuals. If I don't get a positive response back on my 92693 purchase inquiry I'll just go ahead & pick up one of the ECG books. All along I've thought that I had an internal speedo problem and that you had a wiring problem. The further we get, the more that looks to be the case. So I'm now trying to find sources for all of the topside board components (just bought 100 of one of the transistors for <$9 delivered). Trying not to think about the components on the other side though, because I have almost zero familarity with SMDs.

 

I found 3 websites that seem to have the 92693 in stock.

92693 chips new and original IC-in Integrated Circuits from Electronic Components & Supplies on Aliexpress.com | Alibaba Group

Aliexpress.com : Buy 92693 from Reliable 92693 suppliers on YXCHIP | Alibaba Group

INTEGRATO - 92693 | GPEC srl

The second one offers the exact same IC as in the speedo, 92693 H219. However, I would trust much more the third (Italian) website which also has a fantastic choice of vintage components and easy search by number or manufacturer.

With regard to "H219", I don't know if this is important or it just means batch number. According to some forum discussions, 92693 is also used in speedometers of other cars but there was no mention of which cars (only talking about how hard it is to find it and what it is). There is no datasheet anywhere on the web and I only found that the chip is a "Logic IC" and that its application is "Computer"
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The two Alibaba websites were in English when I save them but now, when I opened them from here, they come in Italian. Somehow they know the chip is for a Ferrari.

 

Thanks, Miroljub! It's encouraging to see them being offered. The first two sites came up in English for me. I like the price level much better on the Italian site and I agree that it's probably less risky, but the only Italian I recognize is tiny bits from repair manuals, so I'd be totally lost trying to order them.

Are you now thinking this is a bespoke chip for automotive applications? I kept thinking it was just an op amp or something to drive the speedometer motor (again WAGing based on what little I remember about electronics).

I would like to pick some up, one way or another...

 

You can also get the big IC from the Italian website if you "cerca" (search, your first lesson of Italian) "MC14024BCP" (Motorola) or "HCF4024BE" (SGS or ST). As the Motorola is a bit expensive (0.70 €), you can go for considerably cheaper SGS or ST at 0.60 €.

(PS: If you right click on the page, you can translate it into English)

 

Ha! You know me all too well if you think I'm interested in saving a few cents.

In truth, I found some original Motorolas on eBay. They're more expensive by far, but they're in the States so they'll get here quicker. All along, I've thought the problem was in the speedo-- that's why I checked it first of all. And honestly, I've kinda suspected the larger counter IC, even though it's just a gut feeling and nothing else. So after you posted that it might be the next item on the to-try list I'm willing to pony up for the exact part number to be delivered in fairly short order.

Great tip on right clicking to translate. Had to change browsers to do it (I won't install Google products on my machines but I do have a Chromium based browser I use as a backup and it offers the translate option).

Currently debating between the Italian site and the one with the exact same part number, but leaning toward the latter. Even at inflated retail prices I figure I can replace both ICs and both topside transistors for a fraction of the cost of a new speedo. It'll be well worth the expense if it works and I'm ordering spares of everything, so hopefully I can sell those in the future to offset costs.

Thanks a ton for posting those search results!

 

I tried to buy the chips from the Italian website. As the minimum order is 30 EURO, I was thinking of adding some electronic components for other uses but I could not complete it as it seems to be basically for Italy only. Sent them an email asking whether they would ship internationally and how to pay.

 

Thanks for the update. Gotta leave right now but may try to place an order from the Asian site later.

If the Italian site sells caps you might consider getting those. The 22uF (original 35V) axial lead electrolytic is tough to find in the States. I had to use a radial lead temporarily. Being a perfectionist, I'm going to order 50V axial lead versions from Mouser, but shipping will make the per each cost pretty silly. So if you happen to be able to get them from Italy it might help you make the minimum and save you in the long run if you're intending to re-cap the board at some point.

 

Update: got an email response to my inquiry to one of the places Wade linked to. Shipping is expensive but they're using DHL so hopefully quicker and more reliable than China Post. ICs themselves were quoted at $4 each for 10 chips. They do not list any suffix or other numbers though-- just the 92693. IIRC, they do show it to be an 8 pin DIP.

 

I received a response from the Italian company:

"its order has arrived article 92693 rca we verify and I send her the account pay pal for the payment" (struggling a bit with English, like Mike with Italian).

So, no problem with ordering; send order by email and they will send the address for PayPal payment. The email of the person who replied is: [email protected]

 

I only now noticed that the Italian website shows the 92693 chip as "92693/CA3140". CA3140 is a simple Op-Amp (see attached datasheet), directly replaces the well known 741. It is possible that the code 92693 was used only when supplied to automotive industry (speedometers in some other cars also have 92693).
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This is most interesting indeed, Miroljub. Can you think of any method by which we could determine the probability that they're the same chip? I'm willing to perform tests on my original (mounted to the board, of course) or provide whatever info I can to help, but coming up with a methodology is beyond my knowledge level.

It does seem likely to me though, since the circuit is presumably simple enough that there should have been no need to use a bespoke chip. Then again, we are talking about the Italians, who don't always take the easiest pathway.

I really appreciate your continued sleuthing here. Not only is it of help to me, it will be of benefit to many others in the future since speedometer problems seem to be uncommonly common in 348s.

 

Just sent an email to the Italian supplier ordering the chips and some other parts (they have 22uF blue axial cap, 100V). I also asked if they had a datasheet for 92693 and otherwise whether it is identical to the CA3140 (mentioned, by the way, that I am trying to repair a Ferrari 348 speedo). These Op-Amps are used in power supply regulation (stabilisation) but also as signal amplifiers and conditioners. I cant tell what function it has in the speedo circuit (I don't have mine out as my speedo is fine) but it could be either of the two.

 

I'm thinking to try to determine if the circuit as I interpolate it matches up with the pins on the CA3140 data sheet. As I've said before, I have *very* limited knowledge here, but I'd think that if I could determine that power pins are correct and that an input pin is connected to an output from the counter IC that would serve as supporting evidence that the two chips are the same. Conversely, if it appears that different pins are getting power that would tend to indicate that they're not the same IC. Does this plan have any merit?

Hopefully the Italians will take a sympathetic view of someone trying to repair a Ferrari and provide some info, but trying to think of a fallback method since CA3140s are cheap and readily available.

 

Now that we know all the components, you or Wade (or both then compare) could draw the circuit diagram. It is not really a complicated circuit board. I will inform when I receive response from Italy.