Heathkit IO 4550: Difference between revisions

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The Heathkit IO 4550 is a dual trace 10 MHz oscilloscope sold as a kit for the end user to assemble themselves.
The Heathkit IO 4550 is a dual trace 10 MHz oscilloscope sold as a kit for the end user to assemble themselves.
== Known Issues ==
== Known Issues ==
=== Unit emits smoke and/or a loud bang when powered on ===
=== Unit emits smoke and/or a loud bang when powered on ===
==== Cause ====
==== Cause ====
*Several tantalum capacitors on the power rails fail short circuit
*Several tantalum capacitors on the power rails fail short circuit
Line 21: Line 18:
File:Short circuit tantalum.jpg|alt=Visible and thermal images of a tantalum capacitor that has failed short circuit|Visible and thermal images of a tantalum capacitor that has failed short circuit
File:Short circuit tantalum.jpg|alt=Visible and thermal images of a tantalum capacitor that has failed short circuit|Visible and thermal images of a tantalum capacitor that has failed short circuit
</gallery>
</gallery>
==== Solution ====
==== Solution ====
*Replace all faulty tantalum capacitors on the +/-15 V rails and repair any damage
*Replace all faulty tantalum capacitors on the +/-15 V rails and repair any damage
== Disassembly Notes ==
== Disassembly Notes ==
{{WarnAlt|danger|med|This device contains a high voltage electrostatically deflected [[CRT Repairs|CRT]] with fully exposed high voltage PCBs.}}
{{WarnAlt|danger|med|This device contains a high voltage electrostatically deflected [[CRT Repairs|CRT]] with fully exposed high voltage PCBs.}}
{{WarnAlt|warning|med|This device contains a fully exposed open frame [[Mains Power|mains voltage]] power supply.}}
{{WarnAlt|warning|med|This device contains a fully exposed open frame [[Mains Power|mains voltage]] power supply.}}
*It is recommended you power the +/- 15 V rails with an external bench power supply prior to plugging the device into mains to be able to limit the current draw to prevent damage to shunt regulators from shorted tantalum capacitors.
*It is recommended you power the +/- 15 V rails with an external bench power supply prior to plugging the device into mains to be able to limit the current draw to prevent damage to shunt regulators from shorted tantalum capacitors.
* The PCB does not need to be removed from the chassis to replace capacitors, it is difficult to desolder/solder some capacitors with the board still in the chassis however in order to remove the PCB a number of flying leads and the front panel knobs will probably have to be removed.
* The PCB does not need to be removed from the chassis to replace capacitors, it is difficult to desolder/solder some capacitors with the board still in the chassis however in order to remove the PCB a number of flying leads and the front panel knobs will probably have to be removed.
== Original Parts ==
== Original Parts ==
=== Vertical Circuit Board ===
=== Vertical Circuit Board ===
Line 38: Line 31:


While Healthkit devices come with an assembly manual and components list unfortunately digitized versions on the internet are missing page 27 which contains information about those faulty tantalum capacitors. My unit also included orange tantalum capacitors on other PCBs in the unit however those tested good. The failure of this unit was while it was in the hands of the previous owner, it failed slowly overheating and damaging resistors that form part of a shunt regulator until it failed catastrophically, the previous owner had unsuccessfully attempted a repair by only replacing the one tantalum capacitor that had exploded.
While Healthkit devices come with an assembly manual and components list unfortunately digitized versions on the internet are missing page 27 which contains information about those faulty tantalum capacitors. My unit also included orange tantalum capacitors on other PCBs in the unit however those tested good. The failure of this unit was while it was in the hands of the previous owner, it failed slowly overheating and damaging resistors that form part of a shunt regulator until it failed catastrophically, the previous owner had unsuccessfully attempted a repair by only replacing the one tantalum capacitor that had exploded.
{| class="wikitable"
{| class="wikitable"
|+Capacitor [[Capacitor Specifications|Specifications]] and [[Part Footprints|Footprint]] Information
|+Capacitor [[Capacitor Specifications|Specifications]] and [[Part Footprints|Footprint]] Information
!RefDes
!RefDes
!Qty
!Qty
Line 56: Line 48:
|Tantalum
|Tantalum
|KEMET
|KEMET
|-
|
|7
|1000 μF
|35 V
|Through Hole
|Aluminum Electrolytic
|Rubycon
|}
=== Horizontal Circuit Board ===
{| class="wikitable sortable"
|+Capacitor [[Capacitor Specifications|Specifications]] and [[Part Footprints|Footprint]] Information
!RefDes
!Qty
!Capacitance
!Voltage
![[Part Footprints|Mount]]
!Diameter/Size
!Height
!Lead Spacing
!Temp
![[Capacitor Types|Type]]
!Brand
!Series
|-
|
|
|100 µF
|100 V
|Through Hole Axial
|
|
|
|0 °C
|
|
|
|}
|}


Line 64: Line 94:


Note that those capacitors are not in critical analog parts of the oscilloscope circuit but are used for power rail bulk capacitance. As a result you can pretty much substitute any modern 10 μF 20 V capacitor, I used wet electrolytics that were laying around as the unit is unlikely to be used much, however below are some equivalent tantalum capacitors that should be considered if doing a proper restoration.
Note that those capacitors are not in critical analog parts of the oscilloscope circuit but are used for power rail bulk capacitance. As a result you can pretty much substitute any modern 10 μF 20 V capacitor, I used wet electrolytics that were laying around as the unit is unlikely to be used much, however below are some equivalent tantalum capacitors that should be considered if doing a proper restoration.
{| class="wikitable"
{| class="wikitable"
|+Capacitors
|+Capacitors
Line 76: Line 105:
|T356E106K020AT
|T356E106K020AT
|[https://www.digikey.com/en/products/detail/kemet/T356E106K020AT/818500 Digikey]
|[https://www.digikey.com/en/products/detail/kemet/T356E106K020AT/818500 Digikey]
|-
|
|7
|35PX1000MEFC10X20 / UVR1V102MHD1TO / EKY-350ETD102MK25S
|[https://www.digikey.com/en/products/detail/rubycon/35PX1000MEFC10X20/3563769 DigiKey] [https://www.mouser.com/ProductDetail/Nichicon/UVR1V102MHD1TO?qs=GsRI6e%2FkDqaxg%2FkU%252BUf9rg%3D%3D Mouser] [https://www.lcsc.com/product-detail/Aluminum-Electrolytic-Capacitors-Leaded_NCC-Nippon-Chemi-Con-EKY-350ETD102MK25S_C337467.html LCSC]
|}
=== Horizontal Circuit Board ===
{| class="wikitable sortable"
|+Capacitors
!RefDes
!Qty
!Compatible Part Number
!Order Links
|-
|
|1
|107TMA100M
|[https://www.digikey.com/en/products/detail/cornell-dubilier-illinois-capacitor/107TMA100M/5410809 DigiKey] [https://www.mouser.com/ProductDetail/Cornell-Dubilier-CDE/107TTA100M?qs=3tP%252BN51vMXd0iKsJmSq4fA%3D%3D Mouser]
|}
|}
''If parts are not available or different selection is preferred, you can use the values in the [[Heathkit IO 4550#Original Parts|Original Parts]] section to perform a parametric search.''
''If parts are not available or different selection is preferred, you can use the values in the [[Heathkit IO 4550#Original Parts|Original Parts]] section to perform a parametric search.''
== References ==
== References ==
<references />
<references />
[[Category:1970s]]
[[Category:1970s]]
[[Category:Oscilloscope]]
[[Category:Oscilloscope]]

Revision as of 01:32, 2 March 2023

Heathkit IO 4550
Preliminary Information
Release Year 1978
Leak Risk Unknown
Batteries None
Mounting Technology Through Hole, DIP Sockets, Flying Lead
Capacitor Types Electrolytic, Tantalum, Paper, Ceramic, Polymer, Mylar, Mica
Destructive Entry No
CRT Guides
General Information · Repair Cautions

The Heathkit IO 4550 is a dual trace 10 MHz oscilloscope sold as a kit for the end user to assemble themselves.

Known Issues

Unit emits smoke and/or a loud bang when powered on

Cause

  • Several tantalum capacitors on the power rails fail short circuit
  • Visible and thermal images of a tantalum capacitor that has failed short circuit

    Visible and thermal images of a tantalum capacitor that has failed short circuit

Solution

  • Replace all faulty tantalum capacitors on the +/-15 V rails and repair any damage

Disassembly Notes

danger DANGER This device contains a high voltage electrostatically deflected CRT with fully exposed high voltage PCBs.
warning WARNING This device contains a fully exposed open frame mains voltage power supply.
  • It is recommended you power the +/- 15 V rails with an external bench power supply prior to plugging the device into mains to be able to limit the current draw to prevent damage to shunt regulators from shorted tantalum capacitors.
  • The PCB does not need to be removed from the chassis to replace capacitors, it is difficult to desolder/solder some capacitors with the board still in the chassis however in order to remove the PCB a number of flying leads and the front panel knobs will probably have to be removed.

Original Parts

Vertical Circuit Board

Failed through hole tantalum capacitors

85-1989-2

While Healthkit devices come with an assembly manual and components list unfortunately digitized versions on the internet are missing page 27 which contains information about those faulty tantalum capacitors. My unit also included orange tantalum capacitors on other PCBs in the unit however those tested good. The failure of this unit was while it was in the hands of the previous owner, it failed slowly overheating and damaging resistors that form part of a shunt regulator until it failed catastrophically, the previous owner had unsuccessfully attempted a repair by only replacing the one tantalum capacitor that had exploded.

Capacitor Specifications and Footprint Information
RefDes Qty Capacitance Voltage Mount Type Brand
C114-1, C114-2, C115-1, C115-2, C116-1, C116-2, C123-1, C123-1, C124-1, C124-2 10 10 μF 20 V Through Hole Tantalum KEMET
7 1000 μF 35 V Through Hole Aluminum Electrolytic Rubycon

Horizontal Circuit Board

Capacitor Specifications and Footprint Information
RefDes Qty Capacitance Voltage Mount Diameter/Size Height Lead Spacing Temp Type Brand Series
100 µF 100 V Through Hole Axial 0 °C

Replacement Parts

Vertical Circuit Board

Heathkit IO 4550 before and after capacitor replacement, failed tantalums circled in red.

85-1989-2

Note that those capacitors are not in critical analog parts of the oscilloscope circuit but are used for power rail bulk capacitance. As a result you can pretty much substitute any modern 10 μF 20 V capacitor, I used wet electrolytics that were laying around as the unit is unlikely to be used much, however below are some equivalent tantalum capacitors that should be considered if doing a proper restoration.

Capacitors
RefDes Qty Compatible Part Number Order Links
C114-1, C114-2, C115-1, C115-2, C116-1, C116-2, C123-1, C123-1, C124-1, C124-2 10 T356E106K020AT Digikey
7 35PX1000MEFC10X20 / UVR1V102MHD1TO / EKY-350ETD102MK25S DigiKey Mouser LCSC

Horizontal Circuit Board

Capacitors
RefDes Qty Compatible Part Number Order Links
1 107TMA100M DigiKey Mouser

If parts are not available or different selection is preferred, you can use the values in the Original Parts section to perform a parametric search.

References

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