Topics

DC503 repair (pwr supply and incorrect display)


um-gs@...
 

Hi,
I had to repair a defect DC 503 (S/N B101963) (damaged by power failure).
The display was showing zeros, no reaction on input frequencies.
A check of the internal voltages showed that the - 22V line was at about - 8 V.
Lot of searching and part exchange finally proved that the transistors Q545 and Q548 had degraded in their current amplification so they could not drive the external power transistor in the mainframe.
Replacing both transistors with high beta pnp types ( in this case BC557B) solved the problem - the -22V were back.
After that the inputs were working again, frequency was displayed but showing a strange behaviour - when the input frequency was increased from 1,999 to 2,000, the display jumped to "0", then showing strange values.
This happened in all frequency ranges.
A long search and replacing the (socketed) ICs finally led to the finding that the BCD-line representing "2" in the output BUS of the storage register was shorted to ground. Therefore no "2" value from the BCD-Bus was transferred, all digits could only display 1,4,5,8,9. Removing all Latch ICs U320...U326 (Type 4035) proved that one of them had a shorted output pin 11 which grounded the "2"-BCD bus line.
Removing it solved the malfunction.

Final question: it seems that this IC type Motorola MC4035p is totally obsolete - I couldn't find any replacement or supply. When searching you always get the CMOS type 4035 which is 16 pin and has a totally different function.
Has anybody a resource for the TTL MC4035P type?

Thanks, Gordian


Dave Wise
 

Sure there is replacement available, just at insane price. Boca Semi has them for around $30 each.
I would engineer a substitute using current parts. Do you need open collector? Is tri-state enough? If so, that makes it easier, just use 74-series TTL and rearrange the pins.

Dave Wise
________________________________________
From: TekScopes@groups.io <TekScopes@groups.io> on behalf of um-gs via groups.io <um-gs=arcor.de@groups.io>
Sent: Friday, August 07, 2020 11:14 AM
To: TekScopes@groups.io
Subject: [TekScopes] DC503 repair (pwr supply and incorrect display)

Hi,
I had to repair a defect DC 503 (S/N B101963) (damaged by power failure).
The display was showing zeros, no reaction on input frequencies.
A check of the internal voltages showed that the - 22V line was at about - 8 V.
Lot of searching and part exchange finally proved that the transistors Q545 and Q548 had degraded in their current amplification so they could not drive the external power transistor in the mainframe.
Replacing both transistors with high beta pnp types ( in this case BC557B) solved the problem - the -22V were back.
After that the inputs were working again, frequency was displayed but showing a strange behaviour - when the input frequency was increased from 1,999 to 2,000, the display jumped to "0", then showing strange values.
This happened in all frequency ranges.
A long search and replacing the (socketed) ICs finally led to the finding that the BCD-line representing "2" in the output BUS of the storage register was shorted to ground. Therefore no "2" value from the BCD-Bus was transferred, all digits could only display 1,4,5,8,9. Removing all Latch ICs U320...U326 (Type 4035) proved that one of them had a shorted output pin 11 which grounded the "2"-BCD bus line.
Removing it solved the malfunction.

Final question: it seems that this IC type Motorola MC4035p is totally obsolete - I couldn't find any replacement or supply. When searching you always get the CMOS type 4035 which is 16 pin and has a totally different function.
Has anybody a resource for the TTL MC4035P type?

Thanks, Gordian


Ed
 

Gordian:

Where are you located?

I may have the part in a DC503 that I am planning to part out provided it is socketed.
I may also have one DIY replacement left that I made for the MC4335P in the DC502 which is the same part with a higher temperature rating.
My replacement was made using 1 gate SMT devices so it fit in the same space (for the parts in the DC502).

ed


um-gs@...
 

Morning ed,
I am located in Berlin, Germany. Would be great to organize something.
Greetings,
Gordian


Stephen
 

For what it’s worth, I have another issue with my DC503 (without option 1), but also display related. And U320 to U326, which I all replaced BTW, are all 74173 IC’s. I have no way to check the serial number range for the correct parts number as my unit was made in Holland. 74173 are quite easily available over here.


Colin Herbert
 

There are a couple of issues here. Tek didn't print different manuals for equipment made in different locations, as far as I am aware. However, there _are_ sometimes additions and updates which refer to such equipment. The defining thing about the location of the source factory is the initial letter or number of the serial # of the piece of equipment and I won't repeat this info - it has been made available on this Forum a number of times. If you are looking to see if a particular replacement part is appropriate to your piece of equipment, it probably _is_ appropriate. It is likely to be appropriate to _any_ of the similar equipment. The serial # in any Manual simply refers to the time when Tektronix themselves made the alteration and doesn't mean that a piece of equipment with an earlier serial # shouldn't get the upgrade. Sometimes it is virtually mandatory, as the original part became unobtainable or was prone to failure. It is also important to check for "Change Information" after the yellow divider-page in the back of the Manual. Some of this information may apply to a particular batch of serial #s.
Good Luck, Colin.

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Stephen
Sent: 09 August 2020 10:24
To: TekScopes@groups.io
Subject: Re: [TekScopes] DC503 repair (pwr supply and incorrect display)

For what it’s worth, I have another issue with my DC503 (without option 1), but also display related. And U320 to U326, which I all replaced BTW, are all 74173 IC’s. I have no way to check the serial number range for the correct parts number as my unit was made in Holland. 74173 are quite easily available over here.


Ed
 

The 74173 and CD4035 are different as one is a transparent latch and the other a D type flip flop. It looks like the clock should be compatible between the two devices in that the logic high level on the latch clock is the pass through so the rising edge on the 74173 may be in a place to catch the valid data. The output enable is opposite for the two parts, and power is on different pins. My original test board used a 74LS574 which is a D latch, but I had to invert the enable. I doo not remember if I inverted the clock.

ed


Colin Herbert
 

Further to what I have already posted, I have a DC 503 Service Manual. It looks to me from the "Replaceable Electrical Parts" section that they started off with Motorola parts (they are all Quad latches of one type or another) and at Serial # B110000 changed to Tektronix-made parts, at least for the standard units (i.e. non-Option 1). If you cannot source the Tektronix 156-0398-00, then I would think that the Motorola MC4035P would do substantially the same job, or at least make your DC 503 work. The Motorola part is simply referred to as "QUAD LATCH" whereas the Tek-made part is described as "QUAD LATCH W/TRI STATE OUT UT". I confess to not knowing what this difference might offer and I think the necessity/usefulness of the difference has already been referred to in an earlier post.
I can find no mention of 74173 ICs in my Manual in relation to this part.
Colin.

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Stephen
Sent: 09 August 2020 10:24
To: TekScopes@groups.io
Subject: Re: [TekScopes] DC503 repair (pwr supply and incorrect display)

For what it’s worth, I have another issue with my DC503 (without option 1), but also display related. And U320 to U326, which I all replaced BTW, are all 74173 IC’s. I have no way to check the serial number range for the correct parts number as my unit was made in Holland. 74173 are quite easily available over here.


Stephen
 

I have the manual as well, albeit a copy from TekWiki, and there is no reference either to the 74173. But according to the markings on them, the chips in my unit were all originals from that era (DM74173N), and don’t seem to ever have been replaced. I replaced them with more “recent” 74LS173N.
For what it’s worth, my unit’s serial number is 100530, and it’s not from Holland as I wrote earlier, but from Guernsey.


um-gs@...
 

Thanks for all the feedback.
The manual showes different schematics where the parts change, depending on the S/N:
Below 109999 (my version), U320-326 are Motorola MC4035 PLUS Inverters U337 to drive the enable inputs
Above 110000 , U320-326 are denoted "8551" in the schematic, w/o inverters.

As the 4035P have OC outputs all wired together - could these be combined with a single Tri State Output type?


ArtekManuals <manuals@...>
 

Stephen

Not unusual to have part differences (usually minor)  in the European built units vs the US versions. Most ( if not all)  of the manuals in circulation, that we have and on Tekwiki are US manuals and European manuals are very rare

Dave
manuals@...

On 8/9/2020 9:03 AM, Stephen wrote:
I have the manual as well, albeit a copy from TekWiki, and there is no reference either to the 74173. But according to the markings on them, the chips in my unit were all originals from that era (DM74173N), and don’t seem to ever have been replaced. I replaced them with more “recent” 74LS173N.
For what it’s worth, my unit’s serial number is 100530, and it’s not from Holland as I wrote earlier, but from Guernsey.

--
Dave
Manuals@...
www.ArtekManuals.com
--
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus


Stephen
 

On Sun, Aug 9, 2020 at 03:38 AM, ArtekManuals wrote:


Stephen

Not unusual to have part differences (usually minor)  in the European
built units vs the US versions. Most ( if not all)  of the manuals in
circulation, that we have and on Tekwiki are US manuals and European
manuals are very rare

Dave
manuals@...
Yes, I figured that much. I’m very new to all this, but I’ve never seen a reference to a EU serial number in the manuals I have downloaded. That makes these units a little trickier to troubleshoot (for me). I’m not very good at this to begin with. I don’t even always understand all the concepts in the manuals.
All this is part of a steep learning curve for me.


ArtekManuals <manuals@...>
 

Stephen

Don't worry with the help you get here plus 20 more pieces of test gear from now ( they did warn you  didn't they TM500 series test gear and old oscilloscopes is an addiction for which there are no treatment centers) you will wonder why you didn't start yeas ago...plus it keeps you out of the pubs.

Good luck
Dave
NR1DX
manuals@...

On 8/9/2020 10:46 AM, Stephen wrote:
On Sun, Aug 9, 2020 at 03:38 AM, ArtekManuals wrote:

Stephen

Not unusual to have part differences (usually minor)  in the European
built units vs the US versions. Most ( if not all)  of the manuals in
circulation, that we have and on Tekwiki are US manuals and European
manuals are very rare

Dave
manuals@...
Yes, I figured that much. I’m very new to all this, but I’ve never seen a reference to a EU serial number in the manuals I have downloaded. That makes these units a little trickier to troubleshoot (for me). I’m not very good at this to begin with. I don’t even always understand all the concepts in the manuals.
All this is part of a steep learning curve for me.

--
Dave
Manuals@...
www.ArtekManuals.com
--
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus


Colin Herbert
 

I have original Service Manuals for almost all of the Tektronix gear that I am fortunate (or mad) enough to own. I have just taken a quick look at a few of them and one or two were for Guernsey-made items. All of my Manuals, I think, have the first page bearing the Beaverton address, but my 7B85 Manual has a hand-written serial number "100396" and in the "Change Information & Test Equipment" section at the back there are pages referring to both Beaverton-made and Guernsey-made items. I think that if I went through my entire collection, I might find references to other Guernsey-made and even Heerenveen-made items. It looks to be a biggish job, though, with nearly forty manuals (not that I have hardware corresponding to all of them. I don't own a 465, 465B or 7623 (I have a 7623A), but I do have the manuals).
Colin.

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Stephen
Sent: 09 August 2020 15:46
To: TekScopes@groups.io
Subject: Re: [TekScopes] DC503 repair (pwr supply and incorrect display)

On Sun, Aug 9, 2020 at 03:38 AM, ArtekManuals wrote:


Stephen

Not unusual to have part differences (usually minor) in the European
built units vs the US versions. Most ( if not all) of the manuals in
circulation, that we have and on Tekwiki are US manuals and European
manuals are very rare

Dave
manuals@...
Yes, I figured that much. I’m very new to all this, but I’ve never seen a reference to a EU serial number in the manuals I have downloaded. That makes these units a little trickier to troubleshoot (for me). I’m not very good at this to begin with. I don’t even always understand all the concepts in the manuals.
All this is part of a steep learning curve for me.


Stephen
 

On Sun, Aug 9, 2020 at 04:06 AM, ArtekManuals wrote:


Stephen

Don't worry with the help you get here plus 20 more pieces of test gear
from now ( they did warn you  didn't they TM500 series test gear and old
oscilloscopes is an addiction for which there are no treatment centers)
you will wonder why you didn't start yeas ago...plus it keeps you out of
the pubs.

Good luck
Dave
NR1DX
manuals@...
😂😂😂


Stephen
 

On Sun, Aug 9, 2020 at 04:33 AM, Colin Herbert wrote:

I don't own a
465, 465B or 7623 (I have a 7623A), but
I do have the manuals).
Colin.
And these 3 are some of the ones I do have. 😉


Ravi Moghe
 

Quad latch with w/tri state ut - there would be a control signal on one of the pins of this ic that will make the latch output float at "high" state, irrespective of the state of signal at input pins.

If you google for this type of ic you will tend to find many parts. Additional details that you will need to match for will be operating voltage, bias currents, pin compatibility, open collector output etc.

I could just think of these points at the moment. May share further if I remember anything else.

Warm Regards,


scm@...
 

I don't see where anyone has answered your final question. The answer is NO unless you can guarantee that the Tri-state output will not be in the HIGH state at any time that any OC output is LOW.